ExoMars (Exobiology on Mars)
Background: Establishing whether life ever existed, or is still active on Mars today, is one of the outstanding scientific questions of our time. The ExoMars Program seeks to timely address this and other important scientific goals, and to demonstrate key flight and in situ enabling technologies underpinning European and Russian ambitions for future exploration missions. The ExoMars Program is a cooperative undertaking between ESA (European Space Agency) and the Russian federal space agency, Roscosmos. 1)
Within ESA, ExoMars is an element of the Aurora Exploration Program, an optional program executed under the supervision of the Program Board for Human Spaceflight, Microgravity and Exploration (PBHME). However, the ESA Science Program also participates to ExoMars. The objective of the Aurora Program is to explore Solar System objects having a high potential for the emergence of life. Aurora aims to develop technologies and address scientific questions in a step-wise fashion, seeking to advance the level of technical and scientific readiness with each successive mission.
Within Roscosmos, ExoMars is part of the Russian federal space program and is supported by RAS (Russian Academy of Sciences).
To prepare for future exploration missions and to support the Program’s scientific objectives, ExoMars will achieve the following technology objectives:
• EDL (Entry, Descent, and Landing) of a payload on the surface of Mars
• Surface mobility with a Rover
• Access to the subsurface to acquire samples
• Sample acquisition, preparation, distribution, and analysis.
In addition to these technology objectives already agreed in the Aurora Declaration, the following new technology objectives result from the cooperation with Roscosmos:
• Qualification of Russian ground-based means for deep-space communications in cooperation with ESA’s ESTRACK
• Adaptation of Russian on-board computer for deep space missions and ExoMars landed operations
• Development and qualification of throttleable braking engines for prospective planetary landing missions.
The scientific objectives of ExoMars are:
• To search for signs of past and present life on Mars
• To investigate the water/geochemical environment as a function of depth in the shallow subsurface
• To study martian atmospheric trace gases and their sources.
In addition to these science objectives already agreed in the Aurora Declaration, the following new scientific objective results from the cooperation with Roscosmos:
• To characterise the surface environment.
The ExoMars Program consists of two missions, in 2016 and 2018. ESA and Roscosmos have agreed a well-balanced sharing of responsibilities for the various mission elements. 2)
Table 1: Second ExoMars mission moves to next launch opportunity in 2020 3)
The ExoMars 2016 mission will be launched on a Roscosmos-provided Proton rocket. It includes the TGO (Trace Gas Orbiter) and the EDM (Entry, descent and landing Demonstrator Module), both contributed by ESA. The TGO will carry European and Russian scientific instruments for remote observations, while the EDM will have a European payload for in situ measurements during descent and on the martian surface.
In November 2013, ESA named the EDM Schiaparelli in honor the 19th century Italian astronomer Giovanni Schiaparelli (1835-1910). He observed bright and dark straight-line surface features on Mars which he called ‘canali’. This term was mistakenly translated into English as ‘canal’ instead of ‘channel’, conjuring up images of vast irrigation networks constructed by intelligent beings living on Mars. The controversy ended in the early 20th century, thanks to better telescopes offering a clearer view of the planet. — The name was suggested by a group of Italian scientists to the president of the Italian space agency, ASI, who then proposed it to ESA. Italy is the largest European contributor to the ExoMars program. 4)
The ExoMars 2018 mission will land a Rover, provided by ESA, making use of a DM (Descent Module) contributed by Roscosmos. The DM will travel to Mars on an ESA-provided CM (Carrier Module). Roscosmos will launch the spacecraft composite on a Proton rocket. The Rover will be equipped with a European and Russian suite of instruments, and with Russian RHUs (Radioisotope Heating Units). The Rover will also include a 2 m drill for subsurface sampling and a SPDS (Sample Preparation and Distribution System), supporting the suite of geology and life seeking experiments in the Rover’s ALD (Analytical Laboratory Drawer). The Russian SP (Surface Platform) will contain a further suite of instruments, mainly concentrating on environmental and geophysical investigations. 5)
NASA will also deliver important elements to ExoMars: The Electra UHF (Ultra-High Frequency) radio package on TGO for Mars surface proximity link communications with landed assets (such as the Rover and Surface Platform); engineering support to EDM; and a major part of MOMA (Mars Organic Molecule Analyzer), the organic molecule characterization instrument on the Rover.
Table 2: An overview of some Mars parameters 6)
Spacecraft of ExoMars 2016 mission:
The ExoMars mission is the first ESA-led robotic mission of the Aurora Program and combines technology development with investigations of major scientific interest. The main objectives of this mission are to search for evidence of methane and other trace atmospheric gases that could be signatures of active biological or geological processes and to test key technologies in preparation for ESA's contribution to subsequent missions to Mars. 7)
The ExoMars 2016 mission spacecraft includes the following elements, all developed under the leadership of the prime contractor TAS-I (Thales Alenia Space-Italia). 8)
• TGO (Trace Gas Orbiter), developed by Thales Alenia Space, France
• EDM, developed directly by TAS-I
• MSA (Main Separation Assembly), developed by RUAG.
The TGO accommodates scientific instrumentation for the detection of atmospheric trace gases and the study of their temporal and spatial evolution. In addition, it will provide telecommunications support for the 2016 mission, for the 2018 mission and possible other assets until 2022.
The objectives of the ExoMars 2016 mission are to:
1) Validate landing on the planet Mars with a demonstration capsule weighing about 600 kg, using a control system based on a radar altimeter, and with a carbon fiber shock absorber to attenuate the hard contact with the surface.
2) Gather as much information as possible during entry into the Martian atmosphere.
3) Carry out scientific sampling on the surface for a short period.
4) Observe the Martian atmosphere and surface for two years from the orbiter at an altitude of 400 km.
5) Provide the telecommunication support needed by the rover for the 2018 mission.
The EDM is mainly conceived to demonstrate EDL (Entry Descent and Landing) technologies for future planetary exploration missions. The following technologies are foreseen to be demonstrated:
• TPS (Thermal Protection System)
• PAS (Supersonic Parachute System)
• Radar technologies for ground relative altitude and velocity measurements
• Propulsion technologies for attitude control and braked landing
• Crushable material for impact load attenuation.
Figure 1: Artist's rendition of the deployed ExoMars 2016 Trace Gas Orbiter (TGO) and Schiaparelli – the entry, descent and landing demonstrator module (image credit: ESA, ATG medialag)
TGO (Trace Gas Orbiter)
The technical team behind the ExoMars spacecraft involves companies across more than 20 countries. The prime contractor, Thales Alenia Space Italia, is leading the industrial team building the spacecraft (Ref. 6). As a part of the European industrial team, OHB System AG was responsible for developing the core module of the TGO, which comprises the structure as well as the thermal and propulsion system for the 2016 mission. OHB as member of the core industrial team, is responsible for the major German contribution to ExoMars.
Table 3: Main technical characteristics of the ExoMars Trace Gas Orbiter
NASA's participation in the 2016 ExoMars Trace Gas Orbiter includes two "Electra" telecommunication radios. Used successfully on NASA's Mars Reconnaissance Orbiter, Electra acts as a communications relay and navigation aid for Mars spacecraft. Electra's UHF radios support navigation, command, and data-return needs. 9)
TGO's Electra radios use a design from NASA/JPL with special features for relaying data from a rover or stationary lander to an orbiter passing overhead. Relay of information from Mars-surface craft to Mars orbiters, then from Mars orbit to Earth, enables receiving much more data from the surface missions than would otherwise be possible.
As an example of Electra capabilities, during a relay session between an Electra on the surface and one on an orbiter, the radios can maximize data volume by actively adjusting the data rate to be slower when the orbiter is near the horizon from the surface robot's perspective, faster when it is overhead.
Figure 2: This image shows a step in installation and testing of the first of the orbiter's Electra radios, inside a clean room at Thales Alenia Space, in Cannes, France, in June 2014 (image credit: NASA/JPL-Caltech/ESA/TAS) 10)
RCS (Reaction Control System): TGO requires a challenging propulsion subsystem. The TGO RCS will provide the thrust to the spacecraft for all initial trajectory corrections, DSMs (Deep Space Maneuvers) during the cruise phase to Mars and also the high thrust necessary for the final MOI (Mars Orbit Insertion) maneuver. Subsequently, it shall perform 3-axis attitude control of the TGO once in orbit around Mars for the remainder of its seven year lifetime. 11)
The selected RCS is a helium-pressurized bi-propellant propulsion system utilizing MMH (Monomethylhydrazine) as the fuel and mixed oxides of nitrogen (MON-1) as the oxidizer. The architecture is derived from previous flight proven European applications, however the detailed layout is unique and driven by the specific configuration of the TGO spacecraft and the redundancy needs of the ExoMars 2016 mission.
All RCS architecture and engineering activities have been performed by OHB-System (including all subsystem analyses), while Airbus Defence and Space has responsibility for the mechanical configuration, procurement and manufacturing of equipment, integration and acceptance test to ensure that the system requirements defined by TAS-F are satisfied. The subsystem test program has been defined by OHB-System and performed by Airbus DS at the Airbus DS, OHB-System and TAS facilities. Out of the 92 components comprising the flight RCS, 67 are manufactured by Airbus DS including all tanks and thrusters.
Figure 3: The ExoMars Trace Gas Orbiter and Schiaparelli (top) during vibration testing in 2015, the high-gain antenna is on the right (image credit: ESA, S. Corvaja)
Schiaparelli / EDM (Entry, Descent and Landing Demonstrator Module)
Landing on Mars: Despite a number of prominent US successes since the 1970s, landing on Mars remains a significant challenge. As part of the ExoMars program, a range of technologies has been developed to enable a controlled landing. These include a special material for thermal protection, a parachute system, a radar altimeter system, and a final braking system controlled by liquid-propellant retrorockets. Schiaparelli is designed to test and demonstrate these technologies, in preparation for future missions (Ref. 6).
Three days before reaching Mars, Schiaparelli will separate from TGO and coast towards the planet in hibernation mode, to reduce its power consumption. It will be activated a few hours before entering the atmosphere at an altitude of 122.5 km and at a speed of 21 000 km/h. An aerodynamic heatshield will slow the lander down such that at an altitude of about 11 km, when the parachute is deployed, it will be travelling at around 1650 km/h.
Schiaparelli will release its front heat shield at an altitude of about 7 km and turn on its radar altimeter, which can measure the distance to the ground and its velocity across the surface. This information is used to activate and command the liquid propulsion system once the rear heatshield and parachute has been jettisoned 1.3 km above the surface. At this point, Schiaparelli will still be travelling at nearly 270 km/h, but the engines will slow it to less than 2 km/h by the time it is 2 m above the surface. At that moment, the engines will be switched off and Schiaparelli will freefall to the ground, where the final impact, at just under 11 km/h, will be cushioned by a crushable structure on the base of the lander.
Although Schiaparelli will target the plain known as Meridiani Planum in a controlled landing, it is not guided, and the module has no obstacle-avoidance capability. It has, however, been designed to cope with landing on a terrain with rocks as tall as 40 cm and slopes as steep as 12.5º.
Because Schiaparelli is primarily demonstrating technologies needed for landing, it does not have a long scientific mission lifetime: it is intended to survive on the surface for just a few days by using the excess energy capacity of its batteries. However, a set of scientific sensors will analyse the local environment during descent and after landing, including performing the first measurements of atmospheric particle charging effects, to help understand how global dust storms get started on Mars. A communication link with TGO will provide realtime transmission of the most important operational data measured by Schiaparelli during its descent. Shortly after Schiaparelli lands, TGO will start a main engine burn and will return over the landing site only four sols later. In the meantime, the remainder of the entry, descent and landing data, along with some of the science instrument data, will be sent to Earth via ESA’s Mars Express and NASA satellites already at Mars.
Schiaparelli builds on a heritage of designs that have been evaluated and tested by ESA during earlier ExoMars studies. The module accommodates a series of sensors that will monitor the behaviour of all key technologies during the mission. These technologies include a special material for thermal protection, a parachute system, a radar Doppler altimeter system, and a braking system controlled by liquid propulsion. The data will be sent back to Earth for post-flight reconstruction in support of future European missions to Mars.
Table 4: Main technical characteristics of Schiaparelli – the ExoMars EDM (Entry, Descent and Landing Demonstrator Module)
Figure 4: Photo of the Schiaparelli/EDM structural model which is being lowered onto the Multishaker at ESA/ESTEC (image credit: ESA, A. Le Floc’h, Ref. 4)
Launch preparations: In late December 2015, the ExoMars 2016 Trace Gas Orbiter and Schiaparelli (the entry, descent and landing demonstrator module) travelled aboard two Antonov 124 cargo jets from Turin, Italy, to the Baikonur Cosmodrome in Kazakhstan to be readied for launch in March. 12)
Since then, engineering teams, totaling about 65 people, from Thales Alenia Space (Italy and France), the ExoMars project team, instrument teams, and specialists from the Baikonur Cosmodrome have been steadily working through an intensive and painstaking program of final testing and preparation of the two spacecraft, which at 4.300 kg will be the heaviest spacecraft composite ever to be sent to Mars.
All this has to be completed in time for a launch scheduled for 14 March at the beginning of the 12-day launch window for this mission.
Central to the launch campaign activities is the cleanroom. Almost everything in the cleanroom has been transported from Europe for this launch campaign – hence the need for a third Antonov flight. In addition to the specialist lifting equipment and the ground support trolleys needed to move the two spacecraft, the teams have also had to prepare a dedicated ISO 7 environment cleanroom tent, within the "normal" ISO 8 cleanroom environment, for handling Schiaparelli which, being a Mars lander, must be regularly sampled to check that it satisfies the planetary protection regulations. For analysis of these samples a dedicated microbiological laboratory was brought from Turin and installed close to the cleanroom area.
The readying of the TGO (Trace Gas Orbiter) has included a series of system health checks, such as checking that signals could be sent to all spacecraft units and that they responded. The health of the payload – the four science instruments, ACS, CaSSIS, FREND and NOMAD – was checked in a similar manner by verifying that commands could be sent to them and that these commands were carried out. The flight model of FREND was swapped for the flight spare model.
Another important test that has been completed was with the Trace Gas Orbiter and the launch vehicle adapter. Mechanical fit checks and separation tests had already been done in Cannes last year. Here in Baikonur, the team checked the mechanical connections, and also verified that all electrical circuits were completed.
In parallel, Schiaparelli is also being prepared for launch and is subject to tests similar to those performed on the orbiter. The instruments, sensors (DREAMS and COMARS+) and systems have all been thoroughly checked. A leak test has been carried out. Engineers have uploaded the final software and charged the batteries - since Schiaparelli has no solar panels the fully charged batteries are essential for the surface operations. 13)
The mating of the TGO (Trace Gas Orbiter) and Schiaparelli began on 12 February, 2016 with the two spacecraft having been transferred into the fuelling area, where a mounting platform surrounding the orbiter facilitates the activities that need to be done about 4 m off the ground.
TGO and Schiaparelli are mechanically linked with the MSA (Main Separation Assembly), which attaches to TGO with 27 screws. The MSA holds onto Schiaparelli with three separation mechanisms comprising compressed and angled springs that are held by NEAs (Non-Explosive Actuators). When the NEAs are released on 16 October, as the spacecraft approaches Mars, Schiaparelli will be gently pushed away from TGO, at the same time being imparted with a rotation that will serve to stabilize its atmospheric entry.
Figure 5: The ExoMars 2016 Trace Gas Orbiter (with Schiaparelli on top) being fuelled at the Baikonur Cosmodrome in Kazakhstan (image credit: ESA) 14)
Legend to Figure 5: This spacecraft has one fuel tank and one oxidizer tank, each with a capacity of 1207 liter. When fuelling is complete, the tanks will contain about 1.5 ton of MON (mixed oxides of nitrogen) and 1 ton of MMH (monomethylhydrazine). The propellant is needed for the main engine and the 10 thrusters (plus 10 backup thrusters) that are used for fine targeting and critical maneuvers.
Legend to Figure 6: On March 2, 2016, the Breeze upper stage and spacecraft were encapsulated together within the two fairing halves. Prior to the encapsulation, they were tilted horizontally and the first fairing half was rolled underneath the spacecraft and Breeze, on a track inside the cleanroom. The second fairing half was then lowered into place by means of an overhead crane, encapsulating the payload.
Figure 7: Proton-M rocket with ExoMars 2016 Trace Gas Orbiter and Schiaparelli module at the launch pad in Baikonur, Kazakhstan (image credit: ESA, B. Bethge) 17)
Launch: The European-Russian ExoMars (TGO and the EDM Schiaparelli lander) satellite was launched on March 14, 2016 (09:31 GMT) on a Proton-M/Briz vehicle from the Baikonur Cosmodrome, Kazakhstan. The launch provider was ILS (International Launch Services) KhSC (Khrunichev State Research and Production Space Center). 18) 19) 20)
Orbit: The SCC (ExoMars Spacecraft Composite) will be inserted into a T-2 transfer trajectory to Mars. The arrival on Mars is planned on Oct. 19, 2016 after a 9-month cruise phase.
During the cruise phase, the TGO will support all necessary operations and communications with Earth, and will provide the EDM (Schiaparelli) with the required power/energy. During this period, the EDM will be mostly in hibernation mode to minimize the TGO energy consumption, and nominally will be switched on only for three checkouts: the EDM commissioning checkout few days after the launch, the mid-cruise checkout to verify the EDM health status after the DSM (Deep Space Maneuver), and the preseparation checkout few hours before the separation from the TGO.
The EDM will be released by the TGO three days before the arrival at Mars (i.e. on Oct. 16th, 2016) by means of a 3-points spin-up separation mechanism (MSA). The separation provides a relative velocity higher than 0.3 m/s and a spin rate of 2.5 rpm. The spin rate will allow the EDM for maintaining the attitude needed to reach the Mars atmosphere EIP (Entry Interface Point) with a null angle of attack. The duration of the EDM coast phase (3 days), driven by the TGO need to have enough time to correct its orbit after the EDM separation and prepare the critical MOI ()Mars Orbit Injection) maneuver, is challenging for the EDM as the dispersions, coming from the navigation and from the separation mechanism, will propagate for quite a long time, by increasing the trajectory dispersions at Mars EIP.
During the coast phase, the EDM will be mainly in hibernation mode, to minimize the energy consumption from its batteries. Shortly before the arrival at the Mars EIP, the EDM will wake up from the hibernation to prepare the EDL phase.
The ExoMars Orbiter, TGO, will be inserted into an elliptical orbit around Mars and then sweep through the atmosphere to finally settle into a circular, approximately 400 km altitude orbit ready to conduct its scientific mission; inclination = 74º, period of ~2 hours.
TGO will also serve as a data relay for the second ExoMars mission, comprising a rover and a surface science platform, planned for launch in 2018. It will also provide data relay for NASA rovers.
Figure 8: 2016 has been an eventful and promising year for ESA’s ExoMars mission. After successfully placing the Trace Gas Orbiter into Mars’ orbit on 19 October, the orbiter has sent back its first images, tested its instruments and performed in orbit calibration measurements and health checks (video credit: ESA, published on 13 December 2016)
Legend to Figure 8: The Schiaparelli lander collected almost all of its expected data before its unexpected crash landing on the Martian surface. Crucial lessons will be learnt from this for the recently approved 2020 ExoMars mission, which will put Europe’s first rover on Mars.
The precise cause of the lander loss is still being investigated but preliminary technical investigations have found that the atmospheric entry and slowing down in the early phases went exactly as planned.
In all, since its launch in March 2016, the ExoMars mission has been a mixture of successes and one unexpected set back. Looking ahead, the Trace Gas Orbiter will start aerobraking in March 2017 to gradually slow down over the following months. By the end of 2017, the orbiter will be in a lower, near circular orbit of 400 km and ExoMars’ primary science mission can begin.
• January 6, 2021: Frosty scenes in martian summer. The CASSIS camera onboard the ExoMars Trace Gas Orbiter captured remnant frost deposits in a region near Sisyphi Tholus, in the high southern latitudes of Mars (74ºS/246ºE). 21)
Figure 9: This image was taken during the early morning of a midsummer day in the southern hemisphere. At these high latitudes, carbon dioxide ice and frost develop. Frost can be seen within polygonal cracks in the terrain, a feature that indicates the presence of water ice embedded in the soil. The black spots observed throughout the scene are due to dark soil being pushed through cracks in the carbon dioxide ice as it sublimates – turns directly from solid ice to vapor – in the summer months (image credit: ESA/Roscosmos/CASSIS, , CC BY-SA 3.0 IGO)
- The ExoMars program is a joint endeavor between ESA and Roscosmos.
• August 4, 2020: A new set of images captured this spring by CASSIS (Color and Stereo Surface Imaging System) on the ESA-Roscosmos ExoMars Trace Gas Orbiter shows a series of interesting geological features on the surface of Mars, captured just as the planet passed its spring equinox. 22)
Figure 10: Dune fields in the Green Crater of Mars. The image, taken on 27 April 2020 and centered at 52.3ºS, 351.8ºE, shows part of an impact crater located inside the larger Green Crater in the Argyre quadrangle in the southern hemisphere of Mars (image credit: ESA/ExoMars/CaSSIS)
- The image of Figure 10 reveals an almost black dune field on the right, surrounded by red soils that are partially covered with bright white ice. Gullies, also partially covered with ice, are visible in the crater wall in the center of the image. Scientists are currently investigating the relationship between this seasonal ice and the presence of the gullies. The image was taken just after the spring equinox in the southern hemisphere of Mars, when the southernmost part of the crater (to the right) was almost completely free of ice while the northern part (center) was still partially covered. The southern crater wall has had a longer exposure to the Sun (like on Earth equator-facing slopes receive more sunlight), so the ice in this area recedes faster.
Figure 11: Leaf-like structures in Antoniadi impact crater. This image, captured on 25 March 2020, shows the bottom of the 400 km in diameter Antoniadi impact crater, which is located in the northern hemisphere of Mars in the Syrtis Major Planum region. The blue color of the image, centered at 21.0ºN, 61.2ºE, does not represent the real color of the crater floor but highlights the diversity of the rock composition inside the impact crater (image credit: ESA/ExoMars/CaSSIS)
- In the center of the image (Figure 11) are dendritic structures which look like the veins on oak leaves. These structures, evidence of ancient river networks in this region, protrude from the surface, unlike channels, which are usually sunken in the surface. This is because the channels were filled with harder material – possibly lava – and over time the softer rocks surrounding these branching channels have been eroded, leaving an inverted imprint of this ancient river system.
Figure 12: Argyre impact basin after spring equinox. This image of the Argyre impact basin in the southern highlands of Mars was taken on 28 April 2020 just as Mars had passed its southern hemisphere spring equinox. The seasonal ice in the 800km-long impact basin is receding while the ridge on the right side of the image is still covered with frost. The image is centered at 57.5°S, 310.2°E. The frost-covered ridge is facing the pole, therefore receiving less solar radiation than the neighboring equator-facing slope. On Mars, incoming solar radiation transforms the ice into water vapor directly without melting it first into water in a process called sublimation. Since the north-facing slope (on the left) has had a longer exposure to solar radiation, its ice has sublimated more quickly (image credit: ESA/ExoMars/CaSSIS)
Figure 13: Rock composition in Ius Chasma canyon. The image taken on 5 May 2020 shows a part of the floor of the Ius Chasma canyon, part of the Valles Marines system of canyons that stretches nearly a quarter of the circumference of Mars south of the planet's equator. The Ius Chasma canyon, which can be seen in the image rising up to a ridge on the right side, is about 1000 km long and up to 8 km deep, which makes it more than twice as long and four times as deep as the famous Grand Canyon in the US state of Arizona. The center of this image is located at 8.8ºS, 282.5ºE (image credit: ESA/ExoMars/CaSSIS)
- The beautiful color variations across the floor of Ius Chasma are caused by changes in rock composition. Scientists theorize that the light rocks are salts left behind after an ancient lake evaporated. The information about the rock's composition is useful to scientists as it allows them to retrace the formation history of the canyon.
• July 27, 2020: ESA’s ExoMars Trace Gas Orbiter has spotted new gas signatures at Mars. These unlock new secrets about the martian atmosphere, and will enable a more accurate determination of whether there is methane, a gas associated with biological or geological activity, at the planet. 23)
- The Trace Gas Orbiter (TGO) has been studying the Red Planet from orbit for over two years. The mission aims to understand the mixture of gases that make up the martian atmosphere, with a special focus on the mystery surrounding the presence of methane there.
- Meanwhile, the spacecraft has now spotted never-before-seen signatures of ozone (O3) and carbon dioxide (CO2), based on a full martian year of observations by its sensitive Atmospheric Chemistry Suite (ACS). The findings are reported in two new papers published in Astronomy & Astrophysics, one led by Kevin Olsen of the University of Oxford, UK and another led by Alexander Trokhimovskiy of the Space Research Institute (IKI) of the Russian Academy of Sciences in Moscow, Russia. 24) 25)
- These features are both puzzling and surprising,” says Kevin.
- They lie over the exact wavelength range where we expected to see the strongest signs of methane. Before this discovery, the CO2 feature was completely unknown, and this is the first time ozone on Mars has been identified in this part of the infrared wavelength range.”
- The martian atmosphere is dominated by CO2, which scientists observe to gauge temperatures, track seasons, explore air circulation, and more. Ozone – which forms a layer in the upper atmosphere on both Mars and Earth – helps to keep atmospheric chemistry stable. Both CO2 and ozone have been seen at Mars by spacecraft such as ESA’s Mars Express, but the exquisite sensitivity of the ACS instrument on TGO was able to reveal new details about how these gases interact with light.
- Observing ozone in the range where TGO hunts for methane is a wholly unanticipated result.
- Scientists have mapped how martian ozone varies with altitude before. So far, however, this has largely taken place via methods that rely upon the gas' signatures in the ultraviolet, a technique which only allows measurement at high altitudes (over 20 km above the surface).
- The new ACS results show that it is possible to map martian ozone also in the infrared, so its behavior can be probed at lower altitudes to build a more detailed view of ozone’s role in the planet’s climate.
Figure 14: Spectral signatures of carbon dioxide and ozone at Mars. This graph shows an example of the measurements made by the Atmospheric Chemistry Suite (ACS) MIR instrument on ESA's ExoMars Trace Gas Orbiter (TGO), featuring the spectral signatures of carbon dioxide (CO2) and ozone (O3). The bottom panel shows the data (blue) and a best-fit model (orange). The top panel shows the modelled contributions from a variety of different gases for this spectral range. The deepest lines come from water vapor (light blue). The strongest O3 feature (green) is on the right, and distinct CO2 lines (grey) appear on the left. The locations of strong methane features (orange) are also shown in the modelled contributions, though methane is not observed in the TGO data (image credit: K. Olsen et al. (2020))
Unravelling the methane mystery
- One of the key objectives of TGO is to explore methane. To date, signs of martian methane – tentatively spied by missions including ESA’s Mars Express from orbit and NASA’s Curiosity rover on the surface – are variable and somewhat enigmatic.
- While also generated by geological processes, most of the methane on Earth is produced by life, from bacteria to livestock and human activity. Detecting methane on other planets is therefore hugely exciting. This is especially true given that the gas is known to break down in around 400 years, meaning that any methane present must have been produced or released in the relatively recent past.
Figure 15: How methane is created and destroyed on Mars is an important question in understanding the various detections and non-detections of methane at Mars, with differences in both time and location. Although making up a very small amount of the overall atmospheric inventory, methane in particular holds key clues to the planet’s current state of activity. This graphic depicts some of the possible ways methane might be added or removed from the atmosphere. One exciting possibility is that methane is generated by microbes. If buried underground, this gas could be stored in lattice-structured ice formations known as clathrates, and released to the atmosphere at a much later time (image credit: ESA)
- Methane can also be generated by reactions between carbon dioxide and hydrogen (which, in turn, can be produced by reaction of water and olivine-rich rocks), by deep magmatic degassing or by thermal degradation of ancient organic matter. Again, this could be stored underground and outgassed through cracks in the surface. Methane can also become trapped in pockets of shallow ice, such as seasonal permafrost.
- Ultraviolet radiation can both generate methane – through reactions with other molecules or organic material already on the surface, such as comet dust falling onto Mars – and break it down. Ultraviolet reactions in the upper atmosphere (above 60 km) and oxidation reactions in the lower atmosphere (below 60 km) acts to transform methane into carbon dioxide, hydrogen and water vapor, and leads to a lifetime of the molecule of about 300 years.
- Methane can also be quickly distributed around the planet by atmospheric circulation, diluting its signal and making it challenging to identify individual sources. Because of the lifetime of the molecule when considering atmospheric processes, any detections today imply it has been released relatively recently.
- But other generation and destruction methods have been proposed which explain more localized detections and also allow a faster removal of methane from the atmosphere, closer to the surface of the planet. Dust is abundant in the lower atmosphere below 10 km and may play a role, along with interactions directly with the surface. For example, one idea is that methane diffuses or ‘seeps’ through the surface in localized regions, and is adsorbed back into the surface regolith. Another idea is that strong winds eroding the planet’s surface allows methane to react quickly with dust grains, removing the signature of methane. Seasonal dust storms and dust devils could also accelerate this process.
- Continued exploration at Mars – from orbit and the surface alike – along with laboratory experiments and simulations, will help scientists to better understand the different processes involved in generating and destroying methane.
- “Discovering an unforeseen CO2 signature where we hunt for methane is significant,” says Alexander Trokhimovskiy. “This signature could not be accounted for before, and may therefore have played a role in detections of small amounts of methane at Mars.”
Figure 16: This graph shows a new CO2 spectral feature, never before observed in the laboratory, discovered in the martian atmosphere by the Atmospheric Chemistry Suite (ACS) MIR instrument on ESA's ExoMars Trace Gas Orbiter (TGO). The graph shows the full extent of the magnetic dipole absorption band of the 16O12C16O molecule (one of the various 'isotopologues' of CO2). The top panel shows the ACS MIR spectra (shown in black) along with the modelled contribution of CO2 and H2O (shown in blue); the model is based on the HITRAN 2016 database. The bottom panel shows the difference between data and model, or residuals, revealing the structure of the absorption band in detail. The calculated positions of spectral lines are marked with arrows, in different colors corresponding to different 'branches' of the absorption band (red stands for the P-branch, green for the Q-branch and blue for the R-branch), image credit: A. Trokhimovskiy et al. (2020)
- The observations analyzed by Alexander, Kevin and colleagues were mostly performed at different times to those supporting detections of martian methane. Besides, the TGO data cannot account for large plumes of methane, only smaller amounts – and so, currently, there is no direct disagreement between missions.
- “In fact, we’re actively working on coordinating measurements with other missions,” clarifies Kevin. “Rather than disputing any previous claims, this finding is a motivator for all teams to look closer – the more we know, the more deeply and accurately we can explore Mars’ atmosphere.”
Realizing the potential of ExoMars
- Methane aside, the findings highlight just how much we will learn about Mars as a result of the ExoMars program.
- “These findings enable us to build a fuller understanding of our planetary neighbor,” adds Alexander.
- “Ozone and CO2 are important in Mars’ atmosphere. By not accounting for these gases properly, we run the risk of mischaracterizing the phenomena or properties we see.”
- Additionally, the surprising discovery of the new CO2 band at Mars, never before observed in the laboratory, provides exciting insight for those studying how molecules interact both with one another and with light – and searching for the unique chemical fingerprints of these interactions in space.
- “Together, these two studies take a significant step towards revealing the true characteristics of Mars: towards a new level of accuracy and understanding,” says Alexander.
Figure 17: Comparing the atmospheres of Mars and Earth. Mars is about half the size of Earth by diameter and has a much thinner atmosphere, with an atmospheric volume less than 1% of Earth’s. The atmospheric composition is also significantly different: primarily carbon dioxide-based, while Earth’s is rich in nitrogen and oxygen. The atmosphere has evolved: evidence on the surface suggest that Mars was once much warmer and wetter. - The planets in this graphic are not to scale. Mars atmospheric values are as measured by NASA’s Curiosity rover. (image credit: ESA)
- Understanding if life could have ever existed in such conditions is one of the hot topics of Mars exploration, and for the ESA–Roscosmos ExoMars mission. The ExoMars Trace Gas Orbiter is capable of sniffing out the composition of the planet’s trace gases – which make up less than 1% by volume of a planet’s atmosphere – in minute amounts. Although making up a very small amount of the overall atmospheric inventory, methane in particular holds key clues to the planet’s current state of activity.
- On Earth, living organisms release much of the planet’s methane. It is also the main component of naturally occurring hydrocarbon gas reservoirs, and a contribution is also provided by volcanic and hydrothermal activity. Because of the key role natural biology plays in Earth’s methane production, confirming the existence of methane on Mars, and distinguishing between its potential sources, is a top priority of the ExoMars Trace Gas Orbiter.
Successful collaboration in the hunt for life
- As its name suggests, the TGO aims to characterize any trace gases in Mars’ atmosphere that could arise from active geological or biological processes on the planet, and identify their origin.
- The ExoMars program consists of two missions: TGO, which was launched in 2016 and will be joined by the Rosalind Franklin rover and the Kazachok landing platform, due to lift off in 2022. These will take instruments complementary to ACS to the martian surface, examining the planet’s atmosphere from a different perspective, and share the core objective of the ExoMars program: to search for signs of past or present life on the Red Planet.
- “These findings are the direct result of hugely successful and ongoing collaboration between European and Russian scientists as part of ExoMars,” says ESA TGO Project Scientist Håkan Svedhem.
- “They set new standards for future spectral observations, and will help us to paint a more complete picture of Mars’ atmospheric properties – including where and when there may be methane to be found, which remains a key question in Mars exploration.”
- “Additionally, these findings will prompt a thorough analysis of all the relevant data we’ve collected to date – and the prospect of new discovery in this way is, as always, very exciting. Each piece of information revealed by the ExoMars Trace Gas Orbiter marks progress towards a more accurate understanding of Mars, and puts us one step closer to unravelling the planet’s lingering mysteries.”
Figure 18: Artist’s impression of the ExoMars 2022 rover (foreground), surface science platform (background) and the Trace Gas Orbiter (top). Not to scale (image credit: ESA/ATG medialab)
• June 15, 2020: ESA’s ExoMars Trace Gas Orbiter has detected glowing green oxygen in Mars’ atmosphere – the first time that this emission has been seen around a planet other than Earth. 26)
Figure 19: Artist’s impression of ESA’s ExoMars Trace Gas Orbiter detecting the green glow of oxygen in the martian atmosphere. This emission, spotted on the dayside of Mars, is similar to the night glow seen around Earth’s atmosphere from space (image credit: ESA)
- On Earth, glowing oxygen is produced during polar auroras when energetic electrons from interplanetary space hit the upper atmosphere. This oxygen-driven emission of light gives polar auroras their beautiful and characteristic green hue.
- The aurora, however, is just one way in which planetary atmospheres light up. The atmospheres of planets including Earth and Mars glow constantly during both day and night as sunlight interacts with atoms and molecules within the atmosphere. Day and night glow are caused by slightly different mechanisms: night glow occurs as broken-apart molecules recombine, whereas day glow arises when the Sun’s light directly excites atoms and molecules such as nitrogen and oxygen.
- On Earth, green night glow is quite faint, and so is best seen by looking from an ‘edge on’ perspective – as portrayed in many spectacular images taken by astronauts aboard the International Space Station (ISS). This faintness can be an issue when hunting for it around other planets, as their bright surfaces can drown it out.
Figure 20: Airglow observed from the ISS. Airglow occurs in Earth's atmospheres as sunlight interacts with atoms and molecules within the atmosphere. In this image, taken by astronauts aboard the International Space Station (ISS) in 2011, a green band of oxygen glow is visible over Earth's curve. On the surface, portions of northern Africa are visible, with evening lights shining along the Nile river and its delta (image credit: NASA) .
- This green glow has now been detected for the first time at Mars by the ExoMars Trace Gas Orbiter (TGO), which has been orbiting Mars since October 2016.
- “One of the brightest emissions seen on Earth stems from night glow. More specifically, from oxygen atoms emitting a particular wavelength of light that has never been seen around another planet,” says Jean-Claude Gérard of the Université de Liège, Belgium, and lead author of the new study published in Nature Astronomy.
- “However, this emission has been predicted to exist at Mars for around 40 years – and, thanks to TGO, we’ve found it.”
- Jean-Claude and colleagues were able to spot this emission using a special observing mode of the TGO. One of the orbiter’s advanced suite of instruments, known as NOMAD (Nadir and Occultation for Mars Discovery) and including the ultraviolet and visible spectrometer (UVIS), can observe in various configurations, one of which positions its instruments to point directly down at the martian surface – also referred to as the ‘nadir’ channel.
- “Previous observations hadn’t captured any kind of green glow at Mars, so we decided to reorient the UVIS nadir channel to point at the ‘edge’ of Mars, similar to the perspective you see in images of Earth taken from the ISS,” adds co-author Ann Carine Vandaele of the Institut Royal d'Aéronomie Spatiale de Belgique, Belgium, and Principal Investigator of NOMAD.
- Between 24 April and 1 December 2019, Jean-Claude, Ann Carine and colleagues used NOMAD-UVIS to scan altitudes ranging from 20 to 400 km from the martian surface twice per orbit. When they analyzed these datasets, they found the green oxygen emission in all of them.
Figure 21: Observation and model of green dayglow emission at Mars. The observations, obtained with the TGO's NOMAD instrument using its UVIS channel between April and December 2019, are shown as green dots as a function of altitude, and compared to a theoretical model (red line). Oxygen green dayglow appears to be brightest at 80 km, reaching a second peak around 120 km, and dissipating above 150 km (image credit: J.-C. Gérard et al. (2020))
- “The emission was strongest at an altitude of around 80 kilometers and varied depending on the changing distance between Mars and the Sun,” adds Ann Carine.
- Studying the glow of planetary atmospheres can provide a wealth of information about the composition and dynamics of an atmosphere, and reveal how energy is deposited by both the Sun’s light and the solar wind – the stream of charged particles emanating from our star.
- To better understand this green glow at Mars, and compare it to what we see around our own planet, Jean-Claude and colleagues dug further into how it was formed.
- “We modelled this emission and found that it’s mostly produced as carbon dioxide, or CO2, is broken up into its constituent parts: carbon monoxide and oxygen,” says Jean-Claude. “We saw the resulting oxygen atoms glowing in both visible and ultraviolet light.”
- Simultaneously comparing these two kinds of emissions showed that the visible emission was 16.5 times more intense than the ultraviolet.
- “The observations at Mars agree with previous theoretical models but not with the actual glowing we’ve spotted around Earth, where the visible emission is far weaker,” adds Jean-Claude. “This suggests we have more to learn about how oxygen atoms behave, which is hugely important for our understanding of atomic and quantum physics.”
- This understanding is key to characterizing planetary atmospheres and related phenomena – such as auroras. By deciphering the structure and behavior of this green glowing layer of Mars’ atmosphere, scientists can gain insight into an altitude range that has remained largely unexplored, and monitor how it changes as the Sun’s activity varies and Mars travels along its orbit around our star.
Figure 22: Oxygen emission detected in dayside limb spectra from the UVIS channel of the NOMAD instrument on ESA's ExoMars Trace Gas Orbiter. Different colors show the measurements at different altitudes in the martian atmosphere. Oxygen dayglow appears to be brightest at 80 km, reaching a second peak around 120 km, and dissipating above 150 km. This is the first time that this emission has been seen around a planet other than Earth (image credit: J.-C. Gérard et al. (2020))
- “This is the first time this important emission has ever been observed around another planet beyond Earth, and marks the first scientific publication based on observations from the UVIS channel of the NOMAD instrument on the ExoMars Trace Gas Orbiter,” highlights Håkan Svedhem, ESA’s TGO Project Scientist.
- “It demonstrates the remarkably high sensitivity and optical quality of the NOMAD instrument. This is especially true given that this study explored the dayside of Mars, which is much brighter than the nightside, thus making it even more difficult to spot this faint emission.”
- Understanding the properties of Mars’ atmosphere is not only interesting scientifically, but is also key to operate the missions we send to the Red Planet. Atmospheric density, for example, directly affects the drag experienced by orbiting satellites and by the parachutes used to deliver probes to the martian surface.
- “This type of remote-sensing observation, coupled with in situ measurements at higher altitudes, helps us to predict how the martian atmosphere will respond to seasonal changes and variations in solar activity,” adds Håkan. “Predicting changes in atmospheric density is especially important for forthcoming missions, including the ExoMars 2022 mission that will send a rover and surface science platform to explore the surface of the Red Planet.” 27)
• January 17, 2020: Water reaches Mars' upper atmosphere. Mars once hosted abundant water on its surface but subsequently lost most of it to space. Small amounts of water vapor are still present in the atmosphere, which can escape if they reach sufficiently high altitudes. Fedorova et al. used data from the ExoMars Trace Gas Orbiter spacecraft to determine the distribution of water in Mars' atmosphere and investigate how it varies over seasons. Water vapor is sometimes heavily saturated, and its distribution is affected by the planet's large dust storms. Water can efficiently reach the upper atmosphere when Mars is in the warmest part of its orbit, and this behavior may have controlled the overall rate at which Mars lost its water. 28)
- Mars once harbored an active hydrological cycle, as demonstrated by geological features on its surface, but it no longer holds the quantity of water required to produce such geological imprints . 29) The planet’s bulk inventory of water amounts to a global equivalent layer (GEL) of ~30 m, mostly contained in its polar ice caps. This is less than 10% of the water that once flowed on the surface. Mars’ enhanced concentration of heavy water (semiheavy water five or more times the terrestrial standard), strengthens the hypothesis that most of Mars’ primordial water has escaped over time.
- Water in the atmosphere is a negligible component of the planet’s total water inventory, being equivalent to a global layer 10 µm thick, but nevertheless regulates the dissipation of water over time. Most martian water has been lost to space because its decomposition products (atomic hydrogen and oxygen) reach the upper atmosphere, where they can acquire sufficient thermal energy to overcome the low gravity of Mars (which is about one-third that of Earth’s). Water decomposition is theorized to follow a complex reaction chain involving the recombination of H atoms into H2 on a time scale of centuries, buffering any short-term hydrogen abundance variations. This mechanism has been challenged by observations showing that freshly produced H atoms can reach the exosphere (the uppermost layer where the atmosphere thins out and exchanges matter with interplanetary space) on a monthly time scale. The observed short-term variability of the hydrogen atoms populating the exosphere could be caused by direct deposition of water molecules at altitudes high enough to expose them to sunlight, which subsequently triggers a rapid enhancement of hydrogen atoms in the exosphere.
- Testing this hypothesis requires characterizing the mechanisms contributing to upward water propagation through large-scale atmospheric circulation. One such mechanism is the cold trap imposed (as on Earth) by water ice cloud formation at low altitude, subsequent to water condensation. The condensation is predicted to occur whenever the partial pressure of water vapor exceeds saturation. The vapor pressure law causes the cold trap efficiency to depend heavily on temperature, which eventually limits the amount of water that can be transported to higher altitudes.
- We investigate these processes using occultations of the Sun by the martian atmosphere (henceforth, solar occultations), where the vertical distributions of gases and particles can be directly observed. We used the Atmospheric Chemistry Suite (ACS) on the ExoMars Trace Gas Orbiter (TGO) spacecraft. 30) ACS is an assembly of three infrared spectrometers that together provide continuous spectral coverage from 0.7 to 17 µm, with a spectral resolving power ranging from 10,000 to 50,000. Our dataset was assembled by performing solar occultations with the near-infrared (NIR), mid-infrared (MIR), and thermal infrared in honor of professor V. I. Moroz (TIRVIM) channels of ACS. The NIR channel (0.7 to 1.7 µm) encompasses absorption bands of CO2, H2O, CO, and O2, diagnostic of their molecular concentrations over altitudes of 5 to 100 km, with a vertical resolution of 1 to 3 km. TIRVIM (2 to 17 µm) provides simultaneous information on dust and water ice particle abundance.
Figure 23: Example ACS spectra and retrieved profiles. (A) ACS NIR spectra measured during orbit 2580 (Ls = 197.8º, 47.27ºN, 85.2ºW, local time 17:27) at three example altitudes, labeled in each panel. Synthetic models (blue curves) fitted to the data (red dots) account for the water content, CO2 number density, and atmospheric temperature. The residuals are shown with gray lines. (B) Corresponding retrieved profiles of the H2O mixing ratio, temperature, and saturation ratio derived from them. The profiles of the mass of aerosol particles (ice, blue circles; dust, red dots) per cubic centimeter obtained during the same orbit from ACS TIRVIM data are also shown. All altitudes are above areoid (equipotential surface for Mars, the analog of geoid for Earth), image credit: ACS Research Team
• December 20, 2019: Ice capping the northern hemisphere terrain of Mars slowly recedes as summer progresses, revealing the underlying surface. 31)
- At this time, it was mid-summer in the northern hemisphere of Mars: the carbon dioxide ice cover had retreated, revealing the permanent water ice deposits much more clearly, along with details of surfaces previously covered in ice.
Figure 24: This scene was captured by the CaSSIS camera onboard ESA’s ExoMars Trace Gas Orbiter as it flew over the ice-coated Korolev crater on 1 November 2019. Korolev crater is an 80 km-wide crater in the northern latitudes of Mars that contains a massive ice sheet in its center – this image focuses on one of the crater walls. The image is centered at 164.90ºE/72.02ºN and was taken on 1 November 2019 (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
• December 20, 2019: Many craters in the polar regions of Mars hold permanent ice deposits year-round. 32)
Figure 25: In this image, taken by the CaSSIS camera onboard ESA’s ExoMars Trace Gas Orbiter, the south-eastern wall of a 35 km-wide crater is seen. The image captures its permanent deposits of water ice, which survive the summer months due to the low average sunlight at high latitudes. The image is centered at 192.99ºE/70.4ºN. It was taken on 29 October 2019 (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
• December 20, 2019: The rim of this ice-rich crater catches the early morning sunlight in the high northern latitudes of Mars, imaged by the CaSSIS camera onboard ESA’s ExoMars Trace Gas Orbiter on 26 October 2019. 33)
Figure 26: This image features a simple 7 km-wide bowl-shaped crater pictured in the early morning. The sunlight falling on the ice deposits on the crater’s north-facing walls causes the ice to appear extremely bright. Ice fills much of the crater floor, and coats part of the surrounding terrain (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
- While the image was taken during the summer months, some shadowed regions receive fewer hours of sunlight on average throughout the year, so they trap permanent deposits of water ice.
- The image is centered at 230.77ºE/73.95ºN. It was taken on 26 October 2019. The scale is indicated on the image.
• September 16, 2019: Dunes come in various characteristic shapes on Mars just as on Earth, providing clues about the prevailing wind direction. Monitoring them over time also gives us a natural laboratory to study how dunes evolve, and how sediments in general are transported around the planet. 34)
Figure 27: This captivating image was taken in the north polar region of Mars by the ESA/Roscosmos ExoMars Trace Gas Orbiter’s CaSSIS camera. The image is centered at 74.46ºN/348.3ºE. The image was taken on 25 May 2019 (image credit:ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
- During winter in the polar regions, a thin layer of carbon dioxide ice covers the surface and then sublimates – turns directly from ice into vapor – with the first light of spring. In the dune fields, this springtime defrosting occurs from the bottom up, trapping gas between the ice and the sand. As the ice cracks, this gas is released violently and carries sand with it, forming the dark patches and streaks observed in this CaSSIS image.
- The image also captures ‘barchan’ dunes – the crescent or U-shaped dunes seen in the right of the image – as they join and merge into barchanoid ridges. The curved tips of the barchan dunes point downwind. The transition from barchan to barchanoid dunes tells us that secondary winds also play a role in shaping the dune field.
• May 30, 2019: On 15 June, the ESA-Roscosmos ExoMars Trace Gas Orbiter (TGO) will follow a different path. An ‘Inclination Change Maneuver’ will put the spacecraft in an altered orbit, enabling it to pick up crucial status signals from the ExoMars rover, Rosalind Franklin, due to land on the Red Planet in 2021. 35)
- After completing a complex series of maneuvers during 2017, ExoMars TGO is now orbiting the Red Planet every two hours, collecting scientific data from NASA’s surface-bound rover and lander, and relaying it back to Earth. At the same time, the orbiter is gathering its own data on the planet’s atmosphere, water abundance and alien surface.
- More than a year before Rosalind even lifts off from Earth’s surface, flight dynamics experts at ESA’s ESOC mission control center have formulated a long-term plan to ensure ExoMars TGO can communicate with the new ESA rover and surface platform, contained in the entry, descent and landing module.
- Slight changes to a spacecraft’s orbit have a large effect over time, so while the upcoming maneuvers will only slightly alter TGO’s speed, it will be in the right position to communicate with the then-incoming rover by 2021.
TGO's natural motion
- Mars’ uneven gravity field means that TGO’s orbit ‘wanders’, so it gradually rotates around Mars over time. As illustrated in this image, the spacecraft first follows the black path, then the green, then the red – continuing until it completes an entire rotation around the planet every four and a half months.
- To keep in touch with the descent module as it enters the Martian atmosphere, descends, and lands upon its surface, TGO’s orientation needs to change.
- Three maneuvers in the month of June will alter TGO’s speed, twice by 30.9 m/s and one final small change of 1.5 m/s, bringing it slightly closer to the Martian poles.
Figure 28: Mars' uneven gravity field means that TGO’s orbit 'wanders' (image credit: ESA)
Inclined to fly
- Thanks to these maneuvers, TGO’s path will look more like the second graphic shown here, illustrating ‘snapshots in time’ during the 2021 descent of the new rover. - The green line of Figure 29 represents Rosalind Franklin’s landing approach path. The black line shows the TGO orbit with its optimized orientation, two years after the upcoming maneuvers. The red path shows TGO’s original orbit.
In-phase with Rosalind Franklin
- Once TGO is set to orbit with its new, optimized orientation around Mars, teams on the ground must also ensure it will be on the correct side of the planet when the rover arrives – ‘in phase’ with Rosalind Franklin.
- In February 2021, a small maneuver will be performed to ensure TGO is in the right place at the right time for the lander's arrival. The result of all these maneuvers combined can be seen in Figure 30.
- The black line represents TGO’s orbit around Mars at the time Rosalind Franklin begins descending, shown by the green line. Blue dots along the orbits of both spacecraft are connected by horizontal lines, illustrating their relative positions at different time intervals, and how they are able to ‘see’ each other at every moment, thus ensuring that radio contact can be maintained.
- If teams at mission control were to leave ExoMars TGO in its current orbit, without performing any maneuvers, Mars itself would later get between the orbiting spacecraft and the new Mars explorer.
- In Figure 31, the red line illustrates TGO’s un-phased orbit, and again the green line shows Rosalind Franklin’s entry path and Blue dots represent moments in time for each spacecraft. Lines between the dots reveal how in this scenario, Mars would block their view of each other.
- Without phasing the orbiter with the Mars rover, the two craft will remain invisible to each other at the crucial moment when the rover descends to the surface.
- Not only does the foresight and long-term planning of mission experts ensure communication is maintained between two of ESA’s most important Mars missions, it saves fuel – a huge amount of which would be needed to get TGO in the right position in the weeks or even months before the ExoMars rover's arrival.
- ESA has demonstrated expertise in studying Mars from orbit, now we are looking to secure a safe landing, to rove across the surface and to drill underground to search for evidence of life. Our orbiters are already in place to provide data relay services for surface missions. The next logical step is to bring samples back to Earth, to provide access to Mars for scientists globally, and to better prepare for future human exploration of the Red Planet. This week we’re highlighting ESA’s contribution to Mars exploration as we ramp up to the launch of our second ExoMars mission, and look beyond to completing a Mars Sample Return mission.
• May 30, 2019: The ExoMars rover has a brand new control center in one of Europe’s largest Mars yards. The Rover Operations Control Center (ROCC) was inaugurated today in Turin, Italy, ahead of the rover’s exploration adventure on the Red Planet in 2021. 36)
- The control center will be the operational hub that orchestrates the roaming of the European-built laboratory on wheels, named after Rosalind Franklin, upon arrival to the martian surface on Kazachok, the Russian surface platform.
- “This is the crucial place on Earth from where we will listen to the rover’s instruments, see what she sees and send commands to direct the search for evidence of life on and under the surface,” said Jan Wörner, ESA’s Director General.
- The ExoMars rover will be the first of its kind to both move across the Mars surface and to study it at depth with a drill able to collect samples from down to two meters into the surface.
- The epicenter of the action for directing Mars surface operations on Earth is at the ALTEC (Aerospace Logistics Technology Engineering Company) SpA premises in Turin, Italy. From here, engineers and scientists will work shoulder to shoulder at mission control, right next to a very special Mars yard. Filled with 140 tons of soil, the Mars-like terrain has sandy areas and rocks of various sizes that will help rehearse possible mission scenarios.
Figure 32: Moving off the landing platform (image credit: ALTEC)
Figure 33: Technology image of the week. Constructed within an 8 m long, 2.5 m diameter pressure chamber, the Aarhus Mars Simulation Wind Tunnel has attracted researchers from all over Europe and the United States, to test instruments and equipment for a wide range of Mars missions, including ESA’s ExoMars and NASA’s Mars 2020 rovers (image credit: Aarhus University)
- The air pressure within the wind tunnel can be taken down to less than one hundredth of terrestrial sea level and the temperature reduced to as low as -170°C using liquid nitrogen. Fans then blow the scanty atmosphere that remains at up to 30 m/s, along with Mars-style dust.
- Researchers can evaluate how items such as sensors, solar panels and mechanical parts stand up to the clingy, abrasive particles, sourced from Mars-like, oxide-rich soil found in central Denmark.
- “We’ve been in operation all through this decade,” comments Jonathan Merrison of Aarhus University’s Department of Physics and Astronomy, overseeing the facility. “We’re the only wind tunnel that not only reproduces the low pressure and low temperatures of Mars, but also allows the introduction of particulates of sand and dust.
- “Probably about a third of the testing carried out here has been ExoMars related, then there have been users related to other Mars missions, as well as industrial testing of high altitude terrestrial equipment. We are also a member of the Europlanet network, a grouping of planetary scientists supported by the European Union, supporting the usage of various planetary simulation facilities and analogues.”
- The Aarhus Mars Simulation Wind Tunnel was based on a smaller, earlier version, which remains in use. Its development was supported by ESA’s Technology Development Element program for promising new technologies as well as the philanthropic Villum Kann Rasmussen Foundation.
• May 28, 2019: The ExoMars rover, named Rosalind Franklin, will be the first of its kind to both roam the Mars surface and to study it at depth. Rosalind Franklin will drill down to two meters into the surface to sample the soil, analyze its composition and search for evidence of past – and perhaps even present – life hidden underground. A miniature laboratory inside the rover – the ALD (Analytical Laboratory Drawer) – will analyze the samples with three different instruments, with some baked in the onboard oven to release gases for analysis, a technique used to search for traces of organic compounds. 38)
- The rover will relay its data back to Earth via the ExoMars Trace Gas Orbiter, which is already conducting its science mission from Mars orbit.
Figure 34: The ExoMars rover’s Analytical Laboratory Drawer (ALD) was integrated into the rover at Airbus, Stevenage, UK in May 2019. The video is shown at 18 times real speed; in reality the sequence of events took around 11.5 minutes (video credit: ESA, Airbus, Published on May 28, 2019)
• May 28, 2019: There are few things better than the smell of freshly baked bread from the oven, this is because molecules in the bread disperse in the heat to reach your nose. In a similar way, the ExoMars rover Rosalind Franklin will ‘bake’ and ‘sniff’ martian samples in miniature ovens, imaged above, as part of its investigation of the extra-terrestrial world. 39)
- Set to land on Mars in 2021, Rosalind Franklin will scout areas of interest and drill up to 2 m below the surface and report back its findings to scientists on Earth. Nothing short of a miniature laboratory on wheels, the dirt that Rosalind Franklin collects will pass through different steps in an intricate process allowing for many types of analysis to get the best possible overview of the composition of Mars so far.
- MOMA (Mars Organic Molecule Analyzer) will heat samples to unlock the organic molecules from the Martian dust and transform them into the gas phase. The gas produced will then flow past a receptor that ‘sniffs’ the molecules to learn more about the sample, thanks to its gas chromatograph.
- Baked to up to 800°C in the pyrolysis ovens, the investigations are a one-shot affair. The samples are arranged around the circumference of a rotating carrousel, so that each tube can be placed under the sample funnel and positioned in the tapping station where the samples are ‘cooked’ and ‘sniffed’.
- The thumb-sized gold-colored tubes are hollow to hold the samples. At the tapping station a sphere pushes down on the oven rim to ensure an airtight seal during heating. The double golden pins are the connectors that send electricity running into the ovens.
- The silver-colored rod is a calibration target for a second component of MOMA dubbed ‘LDMS’ that uses laser heating (desorption) and mass spectrometry to analyze the samples. The rod is used to create a standard value for the laser on the Red Planet to ensure that LDMS is working correctly. Together MOMA’s gas chromatographer and LDMS will target biomarkers to answer questions related to the potential origin, evolution and distribution of life on Mars.
- Choosing when and where to take a Martian sample, and choosing which instrument to analyze the sample with, will be a discussion of interplanetary proportions for scientists, but that discussion will need to reach conclusions quickly: the ExoMars rover has 31 tubes to fill and analyze and is designed to work for 218 “sols” or Martian days.
- MOMA is built by a scientific consortium led by the Max-Planck-Institut für Sonnensystemforschung in Göttingen, Germany, with the gas chromatograph built by LISA (Laboratoire Interuniversitaire des Systèmes Atmosphériques) in Paris, France, and the LDMS by NASA’s Goddard Spaceflight Center in Greenbelt, USA. These miniature ovens are part of the rover on-board laboratory “ultra clean zone” that was designed by Thales Alenia Space in Italy, and mounted on a carrousel developed by OHB in Munich, Germany.
Figure 35: Illustration of Martian ovens mounted on a carrousel (image credit: Thales Alenia Space)
• April 10, 2019: New evidence of the impact of the recent planet-encompassing dust storm on water in the atmosphere, and a surprising lack of methane, are among the scientific highlights of the ExoMars Trace Gas Orbiter’s first year in orbit. 40)
Figure 36: Overview of the three new results presented today by the ExoMars TGO (Trace Gas Orbiter teams). While results from the imaging system CaSSIS have been presented previously, today’s release covers the first analysis of the Mars atmosphere and subsurface (image credit: ESA; spacecraft: ESA/ATG medialab)
- TGO’s main science mission began at the end of April 2018, just a couple of months before the start of the global dust storm that would eventually lead to the demise of NASA’s Opportunity rover after 15 years roving the martian surface.
- Spacecraft in orbit, however, were able to make unique observations, with TGO following the onset and development of the storm and monitoring how the increase in dust affected the water vapor in the atmosphere – important for understanding the history of water at Mars over time. 41) 42)
Exploiting the dust storm
- Two spectrometers onboard – NOMAD and ACS – made the first high-resolution solar occultation measurements of the atmosphere, looking at the way sunlight is absorbed in the atmosphere to reveal the chemical fingerprints of its ingredients.
- This enabled the vertical distribution of water vapor and ‘semi-heavy’ water – with one hydrogen atom replaced by a deuterium atom, a form of hydrogen with an additional neutron – to be plotted from close to the martian surface to above 80 km altitude. The new results track the influence of dust in the atmosphere on water, along with the escape of hydrogen atoms into space.
- “In the northern latitudes we saw features such as dust clouds at altitudes of around 25–40 km that were not there before, and in southern latitudes we saw dust layers moving to higher altitudes,” says Ann Carine Vandaele, principal investigator of the NOMAD instrument at the Royal Belgian Institute for Space Aeronomy.
- “The enhancement of water vapor in the atmosphere happened remarkably quickly, over just a few days during the onset of the storm, indicating a swift reaction of the atmosphere to the dust storm.”
Figure 37: TGO's main science mission began at the end of April 2018, just a couple of months before the start of the global dust storm that engulfed the planet. TGO followed the onset and development of the storm and monitored how the increase in dust affected the water vapor in the atmosphere [image credit: ESA; spacecraft: ATG/medialab; data: A-C Vandaele et al (2019)]
Legend to Figure 37: TGO made the first high-resolution solar occultation measurements with its two spectrometers ACS and NOMAD, by looking at the way sunlight is absorbed in the atmosphere to reveal the chemical fingerprints of its ingredients. This enabled the vertical distribution of water vapor and ‘semi-heavy’ water, to be plotted from close to the martian surface to above 80 km altitude – important for understanding the history of water at Mars over time. - The new results track the influence of dust in the atmosphere on water, and provide further insight into the escape of hydrogen atoms into space. The instruments also recorded dust and ice clouds appearing at different altitudes, and a quick enhancement of water vapor in the atmosphere.
- The observations are consistent with global circulation models. Dust absorbs the Sun’s radiation, heating the surrounding gas and causing it to expand, in turn redistributing other ingredients – like water – over a wider vertical range. A higher temperature contrast between equatorial and polar regions is also set up, strengthening atmospheric circulation. At the same time, thanks to the higher temperatures, fewer water-ice clouds form – normally they would confine water vapor to lower altitudes.
- The teams also made the first observation of semi-heavy water simultaneously with water vapor, providing key information on the processes that control the amount of hydrogen and deuterium atoms escaping to space. It also means the deuterium-to-hydrogen (D/H) ratio can be derived, which is an important marker for the evolution of the water inventory on Mars.
- “We see that water, deuterated or not, is very sensitive to the presence of ice clouds, preventing it from reaching atmospheric layers higher up. During the storm, water reached much higher altitudes,” says Ann Carine.“This was theoretically predicted by models for a long time but this is the first time we have been able to observe it.”
- Since the D/H ratio is predicted to change with the season and with latitude, TGO’s continued regional and seasonal measurements are expected to provide further evidence of the processes at play.
Methane mystery plot thickens
- The two complementary instruments also started their measurements of trace gases in the martian atmosphere. Trace gases occupy less than one percent of the atmosphere by volume, and require highly precise measurement techniques to determine their exact chemical fingerprints in the composition. The presence of trace gases is typically measured in ‘parts per billion by volume’ (ppbv), so for the example for Earth’s methane inventory measuring 1800 ppbv, for every billion molecules, 1800 are methane.
- Methane is of particular interest for Mars scientists, because it can be a signature of life, as well as geological processes – on Earth, for example, 95% of methane in the atmosphere comes from biological processes. Because it can be destroyed by solar radiation on timescales of several hundred years, any detection of the molecule in present times implies it must have been released relatively recently – even if the methane itself was produced millions or billions of years ago and remained trapped in underground reservoirs until now. In addition, trace gases are mixed efficiently on a daily basis close to the planet’s surface, with global wind circulation models dictating that methane would be mixed evenly around the planet within a few months.
- Reports of methane in the martian atmosphere have been intensely debated because detections have been very sporadic in time and location, and often fell at the limit of the instruments’ detection limits. ESA’s Mars Express contributed one of the first measurements from orbit in 2004, at that time indicating the presence of methane amounting to 10 ppbv.
- Earth-based telescopes have also reported both non-detections and transient measurements up to about 45 ppbv, while NASA’s Curiosity rover, exploring Gale Crater since 2012, has suggested a background level of methane that varies with the seasons between about 0.2 and 0.7 ppbv – with some higher level spikes. More recently, Mars Express observed a methane spike one day after one of Curiosity’s highest-level readings.
Figure 38: The ExoMars Trace Gas Orbiter’s first analysis of the martian atmosphere at various points around the globe finds an upper limit of methane 10–100 times less than all previous reported detections. The measured data show the sensitivity of the ACS and NOMAD instruments when looking at other molecules, such as water, while methane is apparently absent: the results suggest an upper limit of 0.05 parts per billion (ppbv), — The difference between TGO’s dataset and that of NASA’s Curiosity, which previously reported a seasonal background variation of methane, is presented, noting that the highest sensitivity of TGO’s measurements was achieved before the global dust storm that engulfed the planet in mid 2018, soon after the start of TGO’s science mission. A map with the locations where TGO’s detection attempts were made is also provided, with the majority of measurements taken over high latitudes. - To reconcile the differing results, a better understanding of the different mechanisms able to destroy methane close to the surface of the planet is needed [image credit: ESA; spacecraft: ATG/medialab; data: O. Korablev et al (2019)]
- The new results from TGO provide the most detailed global analysis yet, finding an upper limit of 0.05 ppbv, that is, 10–100 times less methane than all previous reported detections. The most precise detection limit of 0.012 ppbv was achieved at 3 km altitude.
- As an upper limit, 0.05 ppbv still corresponds to up to 500 tons of methane emitted over a 300 year predicted lifetime of the molecule when considering atmospheric destruction processes alone, but dispersed over the entire atmosphere, this is extremely low.
- “We have beautiful, high-accuracy data tracing signals of water within the range of where we would expect to see methane, but yet we can only report a modest upper limit that suggests a global absence of methane,” says ACS principal investigator Oleg Korablev from IKI (Space Research Institute), Russian Academy of Sciences, Moscow.
- “The TGO’s high-precision measurements seem to be at odds with previous detections; to reconcile the various datasets and match the fast transition from previously reported plumes to the apparently very low background levels, we need to find a method that efficiently destroys methane close to the surface of the planet.”
- “Just as the question of the presence of methane and where it might be coming from has caused so much debate, so the issue of where it is going, and how quickly it can disappear, is equally interesting,” says Håkan.
- “We don’t have all the pieces of the puzzle or see the full picture yet, but that is why we are there with TGO, making a detailed analysis of the atmosphere with the best instruments we have, to better understand how active this planet is – whether geologically or biologically.”
Figure 39: This graphic summarizes significant measurement attempts of methane at Mars. Reports of methane have been made by Earth-based telescopes, ESA’s Mars Express from orbit around Mars, and NASA’s Curiosity located on the surface at Gale Crater; they have also reported measurement attempts with no or very little methane detected. More recently, the ESA-Roscosmos ExoMars Trace Gas Orbiter reported an absence of methane, and provided a very low upper limit. - In order to reconcile the range of results, which show variations in both time and location, scientists have to understand better the different processes acting to create and destroy methane (image credit: ESA)
Best map of shallow subsurface water
- While the lively debate on the nature and presence of methane continues, one sure thing is that water once existed on Mars – and still does in the form of water-ice, or as water-hydrated minerals. And where there was water, there might have been life.
- To help understand the location and history of water on Mars, TGO’s neutron detector FREND is mapping the distribution of hydrogen in the uppermost meter of the planet’s surface. Hydrogen indicates the presence of water, being one of the constituents of the water molecule; it can also indicate water absorbed into the surface, or minerals that were formed in the presence of water.
- The instrument’s mapping task will take about one Mars year – almost two Earth years – to produce the best statistics to generate the highest quality map. But the first maps presented based on just a few month’s data already exceed the resolution of previous measurements.
Figure 40: TGO’s first map of shallow subsurface water distribution on Mars. The FREND neutron spectrometer on the ExoMars Trace Gas Orbiter has started mapping the distribution of hydrogen in the uppermost meter of the martian’s surface. Hydrogen indicates the presence of water, being one of the constituents of the water molecule; it can also indicate water absorbed into the surface, or minerals that were formed in the presence of water. A map produced from 131 days data, from 3 May to 10 September 2018, is presented here, covering the globe from 70ºN to 70ºS. - Aside from the obviously water-rich permafrost of the polar regions, the new map provides more refined details of localized ‘wet’ and ‘dry’ regions. It also highlights water-rich materials in equatorial regions that may signify the presence of water-rich permafrost in present times, or the former locations of the planet’s poles in the past [image credit: ESA; spacecraft: ATG/medialab; data: I. Mitrofanov et al (2018)]
- “In just 131 days the instrument had already produced a map that has a higher resolution than that of the 16 years data from its predecessor onboard NASA’s Mars Odyssey – and it is set to continue getting better,” says Igor Mitrofanov, principal investigator of the FREND instrument at the Space Research Institute, Russian Academy of Sciences, Moscow.
- Aside from the obviously water-rich permafrost of the polar regions, the new map provides more refined details of localized ‘wet’ and ‘dry’ regions. It also highlights water-rich materials in equatorial regions that may signify the presence of water-rich permafrost in present times, or the former locations of the planet’s poles in the past.
- “The data is continually improving and we will eventually have what will become the reference data for mapping shallow subsurface water-rich materials on Mars, crucial for understanding the overall evolution of Mars and where all the present water is now,” adds Igor. “It is important for the science on Mars, and it is also valuable for future Mars exploration.”
- “We have already been enjoying beautiful images and stereo views of Mars thanks to the TGO’s imaging system and now we are delighted to share the first look at data from the other instruments,” concludes Håkan. “We have a promising future in contributing to the many fascinating aspects of Mars science, from the distribution of subsurface water, to active surface processes and to the mysteries of the martian atmosphere.”
- For dust devil details, see Figure 41.
• April 8, 2019: Mars may have a reputation for being a desolate world, but it is certainly not dead: its albeit thin atmosphere is still capable of whipping up a storm and, as this image reveals, send hundreds – maybe even thousands – of ‘dust devils’ scurrying across the surface. 43)
- These swirling columns of wind scour away the top layer of surface material and transport it elsewhere. Their course is plotted by the streaks they leave behind – the newly exposed surface material, which is colored in blue/grey in this recent image from the CaSSIS camera onboard the ExoMars Trace Gas Orbiter.
- Dust devils on Mars form in the same way as those on Earth: when the ground gets hotter than the air above it, rising plumes of hot air move through cooler denser air, creating an updraft, with the cooler air sinking and setting up a vertical circulation. If a horizontal gust of wind blows through, the dust devil is triggered. Once whirling fast enough, the spinning funnels can pick up dust and push it around the surface.
Figure 41: As seen in this image, not much can stand in the way of a dust devil: they sweep up the sides of mounds, and down across the floors of impact craters alike. The image was taken on 4 January 2019, and shows a region northeast of Copernicus Crater, in the Cimmeria region of Mars. It captures an area measuring 7.2 x 31 km. North is towards the top left corner in this view. The image has been geometrically rectified and resampled to 4 m/pixel (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
• March 14, 2019: Curious surface features, water-formed minerals, 3D stereo views, and even a sighting of the InSight lander showcase the impressive range of imaging capabilities of the ExoMars Trace Gas Orbiter. 44)
- The ESA-Roscosmos TGO (Trace Gas Orbiter), launched three years ago today, on 14 March 2016. It arrived at Mars on 19 October that year, and spent over a year demonstrating the aerobraking technique needed to reach its science orbit, starting its prime mission at the end of April 2018.
- Showcase of the ExoMars orbiter’s imaging capabilities. For a better overview, the series of images (12) are numbered.
1) Dust devil frenzy:
Figure 42: This remarkable image was taken in the Terra Sabaea region of Mars, west of Augakuh Vallis, by the CaSSIS (Color and Stereo Surface Imaging System) onboard the ESA-Roscosmos ExoMars TGO. This mysterious pattern sits on the crest of a ridge, and is thought to be the result of dust devil activity – essentially the convergence of hundreds or maybe even thousands of smaller martian tornadoes. The image was taken on 8 February 2019 and is centered at 26.36ºN/56.96ºE. North is up (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
Legend to Figure 42: This image is a color-composite representation where features that are bluer compared to the average color of Mars are shown in bright blue hues. In actual color, the streaks would appear dark red. Dust devils churn up the surface material, exposing fresher material below. The reason why the streaks are so concentrated on the ridges is not known at present, but a relationship to orographic lift as masses of carbon dioxide air flow uphill and converge with other air masses is one possibility.
2) Banded terrain:
Figure 43: This image captures a landform on Mars peculiar to the Hellas Basin, sometimes referred to as ‘banded terrain’. The pictured area belongs to the western part of the basin, which contains the lowest lying surfaces on Mars – up to 7 km below the defined zero level. The image was taken by the CaSSIS instrument onboard the ESA-Roscosmos ExoMars TGO on 12 December 2018. It is centered at 39.04ºS/53.9ºE (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
3) Hello InSight: Amongst a new showcase of images from the spacecraft’s CaSSIS, is an image of NASA’s InSight lander – the first time a European instrument has identified a lander on the Red Planet. Insight arrived on Mars on 26 November 2018 to study the interior of the planet. Images of the lander have already been returned by NASA’s Mars Reconnaissance Orbiter; these are the first images from TGO.
Figure 44: ExoMars images InSight. The image shows a panchromatic channel image of the InSight landing site on Mars, acquired by the CaSSIS instrument onboard the ESA-Roscosmos ExoMars TGO on 2 March 2019. The image shows an area of about 2.25 km x 2.25 km in the Elysium Planitia region. The positions of the InSight lander itself, the blast marks from the retro rockets used during landing, the heatshield and the backshell of the entry descent and landing system are marked. It is the first time a European instrument has identified a lander and related equipment on the Red Planet. The original image had a scale of about 4.5 m per pixel, and has been expanded to 2.25 m/pixel for display purposes (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
Legend to Figure 44: The CaSSIS view shows InSight as a slightly brighter dot in the center of the dark patch produced when the lander fired its retro rockets, just before touchdown in the Elysium Planitia region of Mars, and disturbed the surface dust. The heat shield released just before landing can also be seen on the edge of a crater, and the backshell used to protect the lander during descent is also identified.
“The ExoMars Trace Gas Orbiter is being used to relay data from InSight to Earth,” says Nicolas Thomas, CaSSIS Principal Investigator, from the University of Bern in Switzerland. “Because of this function, to avoid uncertainties in communications, we had not been able to point the camera towards the landing site so far – we had to wait until the landing site passed directly under the spacecraft to get this image.”
CaSSIS is expected to provide additional support to the InSight team by observing the surface of Mars in the area surrounding the lander. If the seismometer picks up a signal, the source might be a meteorite impact. One of CaSSIS’s tasks will be to help search for the impact site, which will allow the InSight team to better constrain the internal properties of Mars near the landing site.
The image of InSight also demonstrates that CaSSIS will be able to take pictures of the future ExoMars mission. The mission comprises a rover – named Rosalind Franklin – together with a surface science platform, and is due to be launched in July 2020, arriving at Mars in March 2021. TGO will also act as the data relay for the rover.
4) Salty sulphates:
Figure 45: This image covers a portion of the wall-terrace region of the 100 km-wide Columbus Crater located within Terra Sirenum in the southern hemisphere of Mars. The image was taken by the CaSSIS instrument onboard the ESA-Roscosmos ExoMars TGO on 15 January 2019. The image is centered at 28.79ºS/193.84ºE. North is up (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
Legend to Figure 45: Layered rocks that appear in light-tones are found extensively on the northern crater walls, terraces and floor. These rocks have subsequently been eroded to expose successive layers in cross-section.
The CRISM spectrometer onboard NASA’s Mars Reconnaissance Orbiter has already revealed that these layers contain various hydrated minerals, such as sulphate salts that appear to cover the white-colored rocks. The beige-colored layered rocks, consistent with a sulphate salt signature, appear to line the crater wall, reminiscent of a high water mark.
These ‘bathtub rings’ are consistent with deposits formed by lakes that start to dry up and, through evaporation, begin to deposit specific minerals turn by turn. As the water evaporates, the minerals that are the least readily dissolved in water will begin to precipitate out of the dwindling solution.
The relatively small 1.6 km-wide impact crater towards the top of the image appears to have a small amount of white-colored bedrock exposed in its wall, which CRISM indicates is aluminous clay-bearing material. This suggests that the clay-bearing rocks are older than the sulphate salts that occupy the central portion of this image section.
5) South polar layered terrains:
Figure 46: This image shows the edge of a layered mound in the Burroughs crater on Mars. It is located about 200 km to the northwest of the northernmost edge of the planet’s south polar ice cap. The image was taken by the CaSSIS instrument onboard the ESA-Roscosmos ExoMars TGO and captures a strip of the surface measuring about 25 km x 9 km. The image was taken on 16 December 2018 and is centered at 71.8ºS/114.5ºE (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
Legend to Figure 46: The ‘polar layered deposits’ of Mars, as the ice caps are known, are made of layers upon layers of ice and dust that record how the climate of Mars has evolved in the last few million to hundreds of millions of years.
Many of the impact craters that surround the caps have layered mounds that appear similar to the polar layered deposits, and some, particularly in the north, are known to be composed of nearly pure water ice. Layered mounds, like the one imaged here in the Burroughs crater, lie close to the south polar deposits, and have been less studied than the layers of the caps.
They may represent remnant ice deposits from past climates when the extent of the polar layered deposits reached to lower latitudes, or they may have been deposited independently, which would mean that they represent an entirely separate record of climate – perhaps extending further back into the history of the Mars.
This particular image shows heavily eroded layers toward the northwestern edge of the Burroughs crater mound (north is up). In this orientation, the top of the image contains the crater wall outside of the mound, which is about 400 km lower in elevation than the bottom of the image and shows the mound’s surface.
Because the CaSSIS instrument takes stereo pairs of images, the elevation differences – also between the layers – can be studied with the resulting digital terrain model.
6) Crater floor:
Figure 47: The subtle tints seen in this color-composite image of the floor of Kibuye crater on Mars, in the region of Terra Sirenum, highlight the rich variety of mineralogical composition found in these rocks. The image was taken by the CaSSIS instrument onboard the ESA-Roscosmos ExoMars TGO on 15 December 2018. Chloride salt and clay minerals have been identified here from orbit in the past by infrared spectrometers. CaSSIS color-composite images processed like this one allow scientists to refine the mapping of Mars mineralogy at higher spatial scales. In this region, for example, there is strong evidence for sustained weathering of the rocks by water and possible ancient lakes. Such color-composite images illustrate the extraordinary sensitivity of CaSSIS to the mineralogical composition of the rocks. The image is centered at 29.1ºS/178.2ºE (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
7) A well-preserved crater:
Figure 48: This image was taken by the CaSSIS instrument onboard the ESA-Roscosmos ExoMars TGO on 18 November 2018. Just above the center is a well-preserved 4 km-wide crater. This slice of Mars sits just to the northeast of largest well-preserved impact basin on Mars, Hellas, in the planet’s southern highlands. The image is centered at 28.36ºS/79.75ºE. North is up (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
Legend to Figure 48: The color capability of CaSSIS reveals exposures of light-toned bedrock in this color-composite view. The light-toned bedrock, observed extensively throughout the region, may be associated with the formation of some of the most ancient rocks of the Hellas basin – between 3.7 and 4.1 billion years ago. Many exposures of this terrain show evidence of being altered chemically by water, with phyllosilicate clays being one of the most common minerals formed during this early period of martian history.
8) Mineral diversity:
Figure 49: This colorful image of terrain south of the Mawrth Vallis outflow channel on Mars shows the diversity of mineralogical compositions found in this region. The image was taken by the CaSSIS instrument onboard the ESA-Roscosmos ExoMars TGO on 5 January 2019 and is shown as a color-composite that has been processed to better highlight the different compositions. The image is centered at 21.6°N/341.7°E. North is up (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
Legend to Figure 49: Mawrth Vallis is an outflow channel dissecting the ancient cratered highlands of Mars and leading into the low-lying plains of the northern hemisphere. Some of the bedrock exposed in the sides of the main outflow channel in this view belongs to the most ancient rocks found at the surface of Mars and displays evidence for strong and sustained water activity in the past. Clay minerals are particularly abundant here and provide important clues about the interaction between rock and water on the Red Planet.
9) Layered depressions – 3D:
Figure 50: Use red-blue stereo ‘3D’ glasses to best enjoy this view of circular depressions in the southern hemisphere of Mars, exposing layered outcrops in the northern rim of the large Hellas basin. The image was created from a stereo pair taken by the CaSSIS instrument onboard the ESA-Roscosmos ExoMars TGO on 22 December 2018. The image is aligned from left to right along the ground-track of the spacecraft, and is centered at 29.2ºS/66.8ºE (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
Legend to Figure 50: The geology of the Hellas basin is complex with ancient terrains showing evidences of erosion and sedimentary processes, which might be linked to past water activity. Both the shapes of the features revealed by stereo imaging and the mineralogical composition of the finely layered outcrops are key for understanding their formation processes. CaSSIS color-composite images like these, combined with data from other instruments, help map variations in composition of the surface material.
10) Jezero Crater neighborhood – 3D:
Figure 51: A portion of a crater (left) and rough terrain outside the crater at the boundary between the Syrtis and Isidis regions of Mars, south of the landing site foreseen for NASA’s Mars 2020 rover in Jezero Crater. Use red-blue stereo ‘3D’ glasses to best enjoy this view. It was created from a stereo pair taken by the CaSSIS instrument onboard the ESA-Roscosmos ExoMars TGO on 29 December 2018. The image is centered at 20.73ºN/79.27ºE and measures about 7 km on the short side (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
11) Brain terrain – 3D:
Figure 52: This image features a 4 km-wide impact crater that formed on the rim of an older 15 km-wide crater on Mars. The linear ridge to the top of the image is the rim of the older crater, which itself intersects the rim of an even larger, 40 km-wide crater. The image was created from a stereo pair taken by the CaSSIS instrument onboard the ESA-Roscosmos ExoMars TGO on 7 February 2019. It is centered at 32.9 ºN/13.7ºE (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
Legend to Figure 52: To the left of the image, so-called ‘brain coral terrain’ is visible – so-named because of its likeness in appearance to the ridges on the surface of the human brain. It appears to sit on the floor of the largest crater, although this deposit may be related to the lineated fill that lines the floor of the 15-km crater to the right of the image. Both types of terrain are associated with ice-rich material found near the boundary between Mars’ northern plains and its southern highlands.
Information held in images like these – best viewed with red-blue ‘3D’ glasses to give the impression of depth – help scientists make a detailed study of the order in which the many interacting layers were formed, thus piecing together the history of complex regions.
12) Rocky islands – 3D:
Figure 53: This image shows a part of Tithonium Chasma, on the western side of the Vallis Marineris region – also known as the ‘Grand Canyon’ of Mars. The observed area is part of the Western Tithonium Dome. Rocky outcrops are seen at different elevations – best seen when viewed through red-blue stereo ‘3D’ glasses. The structures have been interpreted as the result of erosion – perhaps by flowing water. Bluer hues indicate dust. The image was created from a stereo pair taken by the CaSSIS instrument onboard the ESA-Roscosmos ExoMars TGO on 5 February 2019 (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
• February 04, 2019: The distinctive form of a delta (Figure 54) arises from sediments that are deposited by a river as it enters slower-moving water, like a lake or a sea, for example. The Nile River delta is a classic example on Earth, and uncannily similar features have been spotted on Saturn’s moon Titan and – closer to home – Mars. While liquid water is no longer present on the surface of Mars, features in the left portion of this image provide strong evidence of it having played an important role in the history of the Red Planet. Furthermore, water-ice is still stable on the surface today, and a recent discovery from Mars Express detected a pocket of liquid water below the surface. 45)
- The 100-meter-thick fan-shaped deposit seen in this image is found in Eberswalde crater in the southern hemisphere of Mars (326.33ºE/23.55ºS). The image covers an area of 31 x 7.5 km and was taken on 16 November 2018 by CaSSIS (Color and Stereo Surface Imaging System) of the ESA-Roscosmos ExoMars Trace Gas Orbiter.
- While presented in beautiful aqueous blues and greens, the image is false-color. The layered rocks that comprise the delta deposits are indicated in white/yellow to purple/blue. The yellow represents the presence of oxidized iron deposits, indicating that the rocks were altered by the presence of water, while the blues signify less altered materials. This suggests that the influence of liquid water reduced over time, perhaps relating to a change in environmental conditions.
Figure 54: Eberswalde crater delta on Mars: This intricate structure of an ancient river delta once carried liquid water across the surface of Mars (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
- After the deposition of the delta sediments in the crater’s ancient lake, fresher sediments – some perhaps deposited by wind – accumulated to cover up a major part of the delta and its connecting channels. These secondary sediments were later eroded in the delta, exposing an inverted relief of the structure that is observed today.
- This particular delta was first observed by NASA's Mars Global Surveyor and has also been imaged by ESA’s Mars Express. It sits inside a 65 km wide impact basin called Eberswalde, which is almost completely buried by material ejected from the much larger and younger nearby Holden Crater.
- Another example of a martian delta can be found in Jezero Crater, which was recently selected as the landing site for the NASA Mars 2020 rover. Meanwhile the ESA-Roscosmos ExoMars rover, also launching in 2020, will target the ancient, once water-rich plains of Oxia Planum. The ExoMars rover will drill down to two meters below the surface to search of clues for past life preserved underground.
- ESA has been exploring Mars for more than 15 years, starting with Mars Express that arrived at the Red Planet at the end of 2003, and which continues to return results today. Meanwhile the Trace Gas Orbiter will complete its first year of science investigations in April; it is sniffing the atmosphere to seek out the faint traces of gases that might be linked to active biological or geological process, and mapping the distribution of underground water-ice. It is also a data relay, providing essential communications infrastructure for current and future surface assets.
- ESA and NASA are also preparing for the next stage of Mars exploration: returning a sample from the Red Planet. NASA’s 2020 rover is set to collect surface samples in small canisters that could later be retrieved by a second mission, and launched into Mars orbit. A third mission would rendezvous with the samples and return them to Earth, where they could be accessed by teams of scientists across the world.
- Long-term planning is crucial to realize the missions that investigate fundamental science questions, and to ensure the continued development of innovative technology, inspiring new generations of European scientists and engineers.
• November 29, 2018: The ExoMars TGO (Trace Gas Orbiter) is all set to receive the first signals from InSight – NASA’s latest inhabitant of Mars. The joint ESA/Roscosmos ExoMars TGO is a research spacecraft orbiting Mars to make a detailed analysis of gases in the martian atmosphere that may be linked to geological or biological activity. The orbiter also relays information from spacecraft exploring the martian surface to teams on Earth, increasing the quantity of data it is possible for us to receive from missions scouring the surface of the Red Planet. 46)
- On Friday 30 November, at 15:20 UTC (16:20 CET), the TGO spacecraft will fly over the stationary new lander, catching the latest data it has gathered during its brief stretch on its new planet. This data from the alien world will be downloaded from the ExoMars TGO when it next comes into view of NASA’s Madrid ground station, later on Monday evening (3 December).
- Nestled within the spacecraft are two Electra radios, one of which is shown in Figure 2. These NASA-built radios include special features that allow data to be relayed between a stationary lander or rover, the orbiting spacecraft, and Earth.
- ESA’s TGO will join NASA orbiters in picking up signals from InSight for the lifetime of its mission, beaming martian data back to Earth as well as forwarding data from Earth to the new InSight lander, and providing the first-ever routine data relay support between missions of different agencies at Mars.
Table 5: Extended life for ESA's science missions 47)
• October 25, 2018: This striking view of layered sediments on Mars was captured by the ExoMars Trace Gas Orbiter’s CaSSIS (Color and Stereo Surface Imaging System) on 2 October 2018. The image, which covers an area 25 x 7 km wide, focuses on a layered mound in Juventae Chasma, just north of the iconic Valles Marineris. 48)
- The features in the chasmata around Valles Marineris have been well studied by Mars orbiters, including ESA’s Mars Express and NASA’s Mars Reconnaissance Orbiter (MRO). The CRISM instrument on MRO detected a significant amount of sulphates at the base of the mound shown in this image – a composition that points to the presence of water in the distant past.
- The new image from CaSSIS reveals the beautiful sedimentary layers in high resolution, allowing scientists to explore the correlation between color as seen by the camera, and composition as determined by previous measurements to better understand how these minerals were deposited in the area. Patterns in the layering can also serve as a record of climate, further constraining the type of environment in which this feature formed, and shedding light on the history of this stunning landscape.
- The ExoMars program is a joint endeavor between ESA and Roscosmos.
Figure 55: Layered mound in Juventae Chasma on Mars captured by CaSSIS on 2 October 2018 (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
• September 19, 2018: Astronauts on a mission to Mars would be exposed to at least 60% of the total radiation dose limit recommended for their career during the journey itself to and from the Red Planet, according to data from the ESA-Roscosmos ExoMars TGO (Trace Gas Orbiter) being presented at the EPSC (European Planetary Science Congress) in Berlin, Germany, this week. 49)
- The orbiter’s camera team are also presenting new images of Mars during the meeting. They will also highlight the challenges faced from the recent dust storm that engulfed the entire planet, preventing high-quality imaging of the surface.
- Radiation monitoring: The TGO began its science mission at Mars in April, and while its primary goals are to provide the most detailed inventory of martian atmospheric gases to date – including those that might be related to active geological or biological processes – its radiation monitor has been collecting data since launch in 2016.
- The Liulin-MO dosimeter of the Fine Resolution Epithermal Neutron Detector (FREND) provided data on the radiation doses recorded during the orbiter’s six-month interplanetary cruise to Mars, and since the spacecraft reached orbit around the planet.
- On Earth, a strong magnetic field and thick atmosphere protects us from the unceasing bombardment of galactic cosmic rays, fragments of atoms from outside our Solar System that travel at close to the speed of light and are highly penetrating for biological material.
- In space this has the potential to cause serious damage to humans, including radiation sickness, an increased lifetime risk for cancer, central nervous system effects, and degenerative diseases, which is why ESA is researching ways to best protect astronauts on long spaceflight missions.
Figure 56: The CaSSIS (Color and Stereo Surface Imaging System) onboard the joint ESA-Roscosmos ExoMars TGO imaged the Ariadne Colles region at 34ºS on 2 September 2018 (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
Legend to Figure 56: The image shows an unusual terrain type – sometimes referred to as chaotic blocks – but what is particularly striking are the large number of dark streaks. One possible interpretation is that these features were produced during the recent dust storm: they could have resulted from dust devils stirring up the surface dust.
- The ExoMars measurements cover a period of declining solar activity, corresponding to a high radiation dose. Increased activity of the Sun can deflect the galactic cosmic rays, although very large solar flares and eruptions can themselves be dangerous to astronauts.
- “One of the basic factors in planning and designing a long-duration crewed mission to Mars is consideration of the radiation risk,” says Jordanka Semkova of the Bulgarian Academy of Sciences and lead scientist of the Liulin-MO instrument.
- “Radiation doses accumulated by astronauts in interplanetary space would be several hundred times larger than the doses accumulated by humans over the same time period on Earth, and several times larger than the doses of astronauts and cosmonauts working on the International Space Station. Our results show that the journey itself would provide very significant exposure for the astronauts to radiation.”
- The results imply that on a six-month journey to the Red Planet, and assuming six-months back again, an astronaut could be exposed to at least 60% of the total radiation dose limit recommended for their entire career.
- The ExoMars data, which is in good agreement with data from Mars Science Laboratory’s cruise to Mars in 2011–2012 and with other particle detectors currently in space – taking into account the different solar conditions – will be used to verify radiation environment models and assessments of the radiation risk to the crewmembers of future exploration missions.
- A similar sensor is under preparation for the ExoMars 2020 mission to monitor the radiation environment from the surface of Mars. Arriving in 2021, the next mission will comprise a rover and a stationary surface science platform. The Trace Gas Orbiter will act as a data relay for the surface assets.
- Global dust storm subsides: Radiation is not the only hazard facing Mars missions. A global dust storm that engulfed the planet earlier this year resulted in severely reduced light levels at the surface, sending NASA’s Opportunity rover into hibernation. The solar-powered rover has been silent for more than three months.
- Orbiting 400 km above the surface, the ExoMars Trace Gas Orbiter’s CaSSIS (Color and Stereo Surface Imaging System) has also suffered. Because the surface of the planet was almost totally obscured by dust, the camera was switched off for much of the storm period.
- “Normally we don’t like to release images like this, but it does show how the dust storm prevents useful imaging of the surface,” says the camera’s Principal Investigator, Nicolas Thomas from the University of Bern. “We had images that were worse than this when we took an occasional look at the conditions, and it didn’t make too much sense to try to look through ‘soup’.”
- But the camera team discovered that even a dust cloud has a silver lining. “The dust-obscured observations are actually quite good for calibration,” says Nicolas. “The camera has a small amount of straylight and we have been using the dust storm images to find the source of the straylight and begin to derive algorithms to remove it.”
- Since 20 August, CaSSIS has started round-the-clock imaging again. “We still have some images affected by the dust storm but it is quickly getting back to normal and we have already had a lot of good quality images coming down since the beginning of September,” adds Nicolas.
- One image acquired on 2 September (Figure 56), although not completely free from artefacts, shows striking dark streaks that might be linked to the storm itself. A possible interpretation is that these features were produced by ‘dust devils’ – whirlwinds – stirring up loose surface material. The region, Ariadne Colles in the southern hemisphere of Mars, was imaged by NASA’s Mars Reconnaissance Orbiter camera in March, before the storm, and there seemed to be little evidence of these streaks.
• September 17, 2018: The image of Figure 57 shows the south-facing rim of a pit crater at 68°S in the Sisyphi Planum region of Mars. It is a color composite made from images acquired on 2 September 2018 by the CaSSIS (Color and Stereo Surface Imaging System) onboard the joint ESA-Roscosmos ExoMars TGO (Trace Gas Orbiter) mission, when the southern hemisphere of Mars was in late spring. 50)
- Most striking are the bright residual carbon dioxide ice deposits on south-facing slopes of the crater. In colder months carbon dioxide and some water vapor freezes on the surface. Then, as the Sun gets higher in the sky again, the ice sublimates away, revealing the underlying surface.
- This particular crater is known to have active gullies – small, incised networks of narrow channels at the rim of the crater that are associated with debris flows. Ice-rich landslide-like flows of material down-slope can be seen in this image – perhaps related to the ‘defrosting’ of the ice as the seasons change.
- Seasonal changes of ice and frost on Mars is one aspect of the ExoMars orbiter’s mission being discussed this week at the European Planetary Science Congress, a major European annual meeting on planetary science, this year hosted by the Technische Universität Berlin, Germany.
Figure 57: The image measures 20 x 8 km with a resolution of 4.5 m/pixel. North is 45º on the upper left. The image was taken at 07:22 AM local solar time on 2 September 2018 and assembled from the RED, PAN and BLU filters (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
• August 24, 2018: This beautiful dune field lies inside a crater near the south polar region of Mars. The image was taken by the ExoMars Trace Gas Orbiter’s CaSSIS (Color and Stereo Surface Imaging System) on 18 May 2018, at the beginning of martian southern spring, when a thin layer of seasonal carbon dioxide ice was still covering the surface. Over the winter, the ice grains in this thin layer appear to grow enough that the ice becomes almost transparent, letting light through and heating up the surface from the bottom of the ice. As the ice begins to sublimate from the bottom up, pressure builds up, and it is released through instabilities and cracks in the ice layer, in what scientists think are geyser-like processes of carbon dioxide gas that push out martian sand. The black streaks seen all across this image are examples of the darker sand being propelled out through the ice cracks and down the slip face of the dunes. 51)
Figure 58: This CaSSIS image was acquired on 18 May 2018, showing a dune field inside a crater near the south polar region of Mars (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
• July 16, 2018: The Rt Hon Theresa May, Prime Minister of the UK, examines the ESA ExoMars rover in the Space Zone at the Farnborough International Airshow, accompanied by ESA Director General Jan Wörner, ESA astronaut Tim Peake and Chief Executive of the UK Space Agency Dr Graham Turnock, 16 July 2018. 52)
Figure 59: UK PM Theresa May with ESA Exomars Rover at Farnborough Airshow 2018 (image credit: ESA)
• June 27, 2018: The ExoMars Trace Gas Orbiter showing the region where the ancient Uzboi Vallis enters the Holden crater in the southern hemisphere of Mars. The valley begins on the northern rim of the Argyre basin and was formed by running water. The fluvial deposits are clearly visible in the impact cratered terrain. 53)
Figure 60: The image was taken by the orbiter’s CaSSIS (Color and Stereo Surface Imaging System) on 31 May 2018 and captures an approximately 22.7 x 6.6 km segment centered at 26.8ºS/34.8ºW. North is to the bottom left in this orientation (image credit: ESA/Roscosmos/CaSSIS , CC BY-SA 3.0 IGO)
• June 4, 2018: The poles of Mars have huge ice caps that are similar to Earth’s polar caps in Greenland and Antarctica. These caps are composed primarily of water ice and were deposited in layers that contain varying amounts of dust. They are referred to as the martian Polar Layered Deposits (PLD). 54)
- Thanks to massive canyons that dissect the layered deposits, orbiting spacecraft can view the layered internal structure. The ExoMars orbiter’s CaSSIS (Color and Stereo Surface Imaging System) viewed this 7 x 38 km segment of icy layered deposits near the margin of the South PLD, which extend as far north as 73ºS.
- Here, CaSSIS has imaged remnant deposits within a crater at this margin. The beautiful variations in color and brightness of the layers are visible through the camera’s color filters. It highlights the bright ice and the redder sandy deposits toward the top of the image.
- The ExoMars program is a joint endeavor between ESA and Roscosmos.
Figure 61: The ExoMars TGO (Trace Gas Orbiter) captured this view of part of the south polar ice cap on Mars on 13 May 2018 (image credit: ESA/Roscosmos/CaSSIS , CC BY-SA 3.0 IGO)
• April 26, 2018: The ExoMars TGO (Trace Gas Orbiter) has returned the first images of the Red Planet from its new orbit. The spacecraft arrived in a near-circular 400 km altitude orbit a few weeks ago ahead of its primary goal to seek out gases that may be linked to active geological or biological activity on Mars. 55)
- The orbiter's CaSSIS (Color and Stereo Surface Imaging System) took this stunning image, which features part of an impact crater, during the instrument’s test period. The camera was activated on 20 March and was tested for the start of its main mission on 28 April.
- “We transmitted new software to the instrument at the start of the test phase and after a couple of minor issues, the instrument is in good health and ready to work,” says the camera’s principal investigator, Nicolas Thomas from the University of Bern in Switzerland.
- The image captures a 40 km-long segment of Korolev Crater located high in the northern hemisphere. The bright material on the rim of the crater is ice.
- “We were really pleased to see how good this picture was given the lighting conditions,” says Antoine Pommerol, a member of the CaSSIS science team working on the calibration of the data. “It shows that CaSSIS can make a major contribution to studies of the carbon dioxide and water cycles on Mars.”
- “We aim to fully automate the image production process,” says Nick. “Once we achieve this, we can distribute the data quickly to the science community for analysis.” - The team also plans to make regular public releases.
Figure 62: The ExoMars CaSSIS (Color and Stereo Surface Imaging System) captured this view of the rim of Korolev crater (73.3ºN/165.9ºE) on 15 April 2018. The image is a composite of three images in different colors that were taken almost simultaneously. They were then assembled to produce this color view. The original image has a nominal scale of 5.08 m/pixel and was re-projected at a resolution of 4.6 m/pixel to create the final version. The dimensions are therefore about 10 x 40 km. The image was taken with a ground-track velocity of 2.90 km/s. The solar incidence angle was 76.6º at a local solar time of 07:14:11 (image credit: ESA/Roscosmos/CaSSIS). In this orientation, north is off-center to the upper left.
- The orbiter’s camera is one of four instruments on the Trace Gas Orbiter, or TGO, which also hosts two spectrometer suites and a neutron detector.
- The spectrometers began their science mission on 21 April with the spacecraft taking its first ‘sniff’ of the atmosphere. In reality, the sniffing is the spectrometers looking at how molecules in the atmosphere absorb sunlight: each has a unique fingerprint that reveals its chemical composition.
- A long period of data collection will be needed to bring out the details, especially for particularly rare – or not even yet discovered – ingredients in the atmosphere. Trace gases, as hinted at from their name, are only present in very small amounts: that is, less than one percent of the volume of the planet’s atmosphere. In particular, the orbiter will seek evidence of methane and other gases that could be signatures of active biological or geological activity.
- The camera will eventually help characterize features on the surface that may be related to trace gas sources. “We are excited to finally be starting collecting data at Mars with this phenomenal spacecraft,” says Håkan Svedhem, ESA’s TGO project scientist. “The test images we have seen so far certainly set the bar high.”
• April 9, 2018: The ExoMars orbiter will soon begin its search for gases that may be linked to active geological or biological activity on the Red Planet. The TGO (Trace Gas Orbiter) has reached its final orbit after a year of ‘aerobraking’ that ended in February. This exciting operation saw the craft skimming through the very top of the upper atmosphere, using drag on its solar wings to transform its initial highly elliptical four-day orbit of about 200 x 98,000 km into the final, much lower and near-circular path at about 400 km. 56)
- It is now circling Mars every two hours and, after calibration and installation of new software, it will begin routine scientific observations. “This is a major milestone for our ExoMars program, and a fantastic achievement for Europe,” says Pia Mitschdoerfer, Trace Gas Orbiter mission manager. “We have reached this orbit for the first time through aerobraking and with the heaviest orbiter ever sent to the Red Planet, ready to start searching for signs of life from orbit.”
- “We will start our science mission in just a couple of weeks and are extremely excited about what the first measurements will reveal,” says Håkan Svedhem, the orbiter’s project scientist. “We have the sensitivity to detect rare gases in minute proportions, with the potential to discover if Mars is still active today – biologically or geologically speaking.”
- The primary goal is to take a detailed inventory of trace gases – those that make up less than 1% of the total volume of the planet’s atmosphere. In particular, the orbiter will seek evidence of methane and other gases that could be signatures of active biological or geological activity.
- On Earth, living organisms release much of the planet’s methane. It is also the main component of naturally occurring hydrocarbon gas reservoirs, and a contribution is also provided by volcanic and hydrothermal activity.
- Methane on Mars is expected to have a rather short lifetime – around 400 years – because it is broken down by ultraviolet light from the Sun. It also reacts with other species in the atmosphere, and is subject to mixing and dispersal by winds. That means, if it is detected today, it was likely created or released from an ancient reservoir relatively recently.
Figure 63: The ExoMars Trace Gas Orbiter is set to analyze the martian atmosphere, in particular trace gases like methane. Although making up a very small amount of the overall atmospheric inventory, methane in particular holds key clues to the planet’s current state of activity. This graphic depicts some of the possible ways methane might be added or removed from the atmosphere. One exciting possibility is that methane is generated by microbes. If buried underground, this gas could be stored in lattice-structured ice formations known as clathrates, and released to the atmosphere at a much later time (image credit: ESA/ATG medialab)
Legend to Figure 63: Methane can also be generated by reactions between water and olivine-rich rocks, perhaps in combination with warmer, volcanic environments. Again, this could be stored underground in icy cages, and outgassed through cracks in the surface – or through volcanoes. Ultraviolet radiation can both break down the methane and generate it through reactions with other molecules or organic material already on the surface, such as comet dust falling onto Mars. Methane can also be quickly distributed around the planet by strong winds, ‘diluting’ its signal and making it challenging to identify individual sources.
Methane on Mars is expected to have a rather short lifetime – around 400 years – so any detections imply it must have been produced or released relatively recently. The Trace Gas Orbiter will build up a picture over time of the methane distribution, to understand geographic and seasonal distributions, and eventually home in on areas where it might be originating.
The spacecraft has the capability to detect and analyze methane and other trace gases, even in low concentrations, with an improved accuracy of three orders of magnitude compared to previous measurements. Furthermore, it will be able to detect key ‘isotopologues’ of methane and water (isotopologues are molecules that have at least one atom with a different number of neutrons than the parent chemical species) to help distinguish between the different formation scenarios.
Figure 64: The ExoMars Trace Gas Orbiter will use a neutron detector, namely FREND (Fine Resolution Epithermal Neutron Detector), to map subsurface hydrogen to a depth of 1 m to reveal deposits of water-ice hidden just below the surface (image credit: ESA/ATG medialab)
Legend to Figure 64: The graphic shows a simple representation of the detection process. Cosmic rays constantly bombard the surface of Mars; they knock neutrons out of the atoms they encounter on the surface and underneath. If water or frozen water-ice is present, hydrogen atoms cause multiple reflections in their paths through the subsurface, slowing down the neutrons. While some neutrons are captured in the subsurface, others escape back out into space. The speeds at which they arrive at the detector on TGO help determine the nature of the subsurface: those that have interacted with water will have lost some of their energy, and be travelling relatively slower than those that have not.
- The four instruments will make complementary measurements of the atmosphere, surface and subsurface. Its camera will help to characterize features on the surface that may be related to trace-gases sources.
- Its instruments will also look for water-ice hidden just below the surface, which along with potential trace gas sources could guide the choice for future mission landing sites.
- It will also soon start providing communication relay for NASA’s Opportunity and Curiosity rovers, ahead of the arrival of NASA’s InSight lander later this year, and for the ExoMars rover and surface science platform in March 2021.
- Preliminary relay tests with NASA’s rovers were conducted in November 2016, shortly after the orbiter’s arrival at Mars. Eventually, it will provide multiple data relay connections each week. — The ExoMars program is a joint endeavor between ESA and Roscosmos.
• February 21, 2018: ESA is reporting that the ”surfing is complete” — referring to ”the 'aerobraking campaign' during which we commanded ExoMars to dip into the wispy, upper-most tendrils of the atmosphere once per revolution, slowing the craft and lowering its orbit,” says ESA flight director Michel Denis. 57)
- “This took advantage of the faint drag on the solar wings, steadily transforming the orbit. It’s been a major challenge for the mission teams supported by European industry, but they’ve done an excellent job and we’ve reached our initial goal. During some orbits, we were just 103 km above Mars, which is incredibly close.”
- The end of this effort came at 17:20 GMT on 20 February, when the spacecraft fired its thrusters for about 16 minutes to raise the closest approach to the surface to about 200 km, well out of the atmosphere. This effectively ended the aerobraking campaign, leaving it in an orbit of about 1050 km x 200 km.
- “Aerobraking works only because we spent significant time in the atmosphere during each orbit, and then repeated this over 950 times,” says Michel. “Over a year, we’ve reduced the speed of the spacecraft by an enormous 3600 km/h, lowering its orbit by the necessary amount.”
- Trimming: In the next month, the control team will command the craft through a series of up to 10 orbit-trimming maneuvers, one every few days, firing its thrusters to adjust the orbit to its final two-hour, circular shape at about 400 km altitude, expected to be achieved around mid-April.
Figure 65: CaSSIS (Color and Stereo Surface Imaging System) is the high-resolution camera on the ExoMars Trace Gas Orbiter. It is capable of acquiring color stereo images of surface features possibly associated with trace gas sources and sinks in order to better understand the range of processes that might be related to trace gas emission. - This image shows the principle of stereo image acquisition. It takes an image looking slightly forwards, and then the camera is rotated to look ‘back’ to take the second part of the image, in order to see the same region of the surface from two different angles. By combining the image pair, information about the relative heights of the surface features can be seen (image credit: University of Bern)
- The initial phases of science gathering, in mid-March, will be devoted to checking out the instruments and conducting preliminary observations for calibration and validation. The start of routine science observations should happen around 21 April.
- “Then, the spacecraft will be reoriented to keep its camera pointing downwards and its spectrometers towards the Sun, so as to observe the Mars atmosphere, and we can finally begin the long-awaited science phase of the mission,” says Håkan Svedhem, ESA’s project scientist.
- The main goal is to take a detailed inventory of trace gases, in particular seeking out evidence of methane and other gases that could be signatures of active biological or geological activity.
- A suite of four science instruments will make complementary measurements of the atmosphere, surface and subsurface. Its camera will help to characterize features on the surface that may be related to trace-gases sources, such as volcanoes. - It will also look for water-ice hidden just below the surface, which along with potential trace gas sources could guide the choice for future mission landing sites.
- Long-distance calls: April will also see the spacecraft test its data-relay capability, a crucial aspect of its mission at Mars.
- A NASA-supplied radio relay payload will catch data signals from US rovers on the surface and relay these to ground stations on Earth. Data relaying will get underway on a routine basis later in the summer.
- Starting in 2021, once ESA’s own ExoMars rover arrives, the orbiter will provide data-relay services for both agencies and for a Russian surface science platform. - ExoMars is a joint endeavor between ESA and Roscosmos.
• February 1, 2018: According to Armelle Hubault, the Spacecraft Operations Engineer on the TGO flight control team, the ExoMars mission has made tremendous progress and is well on its way to establishing its final near-circular orbit at an altitude of ~400 km around the Red Planet. 58)
- The graphic of Figure 66 provides a very concise visualization of the fantastic progress we’ve made with aerobraking to date. It was coded by my ExoMars TGO colleague Johannes Bauer; the bold grey lines show successive reductions in the ExoMars TGO orbital period by 1 hour; the thin lines by 30 minutes.
- We started on the biggest orbit with an apocenter (the furthest distance from Mars during each orbit) of 33,200 km and an orbit of 24 hours in March 2017, but had to pause last summer due to Mars being in conjunction.
- We recommenced aerobraking in August 2017, and are on track to finish up in the final science orbit in mid-March 2018. As of today, 30 Jan 2018, we have slowed ExoMars TGO by 781.5 m/s.
- On 30 Jan. 2018 at 15:35 CET (Central European Time), the spacecraft was where the red dot is, coming out of pericenter passage (passing through the point of closest approach over the surface – where Mars’ thin, uppermost atmosphere drags on the craft the most to give the braking effect).
- The blue line is the current orbit, which takes only 2 hrs and 48 min and with the apocenter reduced to 2700 km; the red line shows the final aerobraking orbit we expect to achieve later in March. Then, we will use the thrusters to maneuver the spacecraft into the green orbit (roughly 400 km circular) – the final science and operational data relay orbit. - The image is pretty much to scale.
- We have to adjust our pericenter height regularly, because on the one hand, the martian atmosphere varies in density (so sometimes we brake more and sometimes we brake less) and on the other hand, martian gravity is not the same everywhere (so sometimes the planet pulls us down and sometimes we drift out a bit). We try to stay at about 110 km altitude for optimum braking effect.
- To keep the spacecraft on track, we upload a new set of commands every day – so for us, for flight dynamics and for the ground station teams, it’s a very demanding time!
- When TGO skims through the atmosphere, it has to adopt a specific orientation to optimize the braking effect and to make sure it stays stable and does not start to spin madly, which would not be optimal. — We are basically using the solar panels as ‘wings’ to slow us down and circularize the orbit.
- The main challenge at the moment is that, since we never know in advance how much the spacecraft is going to be slowed during each pericenter passage, we also never know exactly when it is going to reestablish contact with our ground stations after pointing back to Earth.
- We are working with a 20-min ‘window’ for acquisition of signal (AOS), when the ground station first catches TGO’s signal during any given station visibility, whereas normally for interplanetary missions we have a firm AOS time programmed in advance.
- With the current orbital period now just below 3 hrs, we go through this little exercise 8 times per day!
• January 24, 2018: In 2013, the European Space Agency and Roscosmos—the Russian governmental body responsible for space research—agreed to cooperate on ExoMars, the first joint interplanetary mission between ESA and Russia. This project now involves scientists from 29 research organizations, including MIPT (Moscow Institute of Physics and Technology) and the IKI (Space Research Institute) of the Russian Academy of Sciences (RAS), which is the leading contributor of hardware and equipment on the Russian side. By now, the first package of observation instruments has been delivered into Mars orbit to seek minor chemical components of the planet's atmosphere that may be traces of primitive life (Ref. 99). 59)
- Even if the new data prove to be inconclusive, they will definitely heat up the discussion on whether there ever was life on the red planet. In early 2018, the ExoMars satellite with research instruments on board will lower into its operational orbit and begin observations of the Martian atmosphere. A recent article in Space Science Reviews describes the makeup and objectives of one of the two Russian-built instruments carried by the orbiter.
- The ExoMars joint space mission of ESA and Roscosmos involves two phases. The first one started on March 14, 2016, with the launch of a Proton-M booster rocket from Russia's space complex in Baikonur, Kazakhstan. The rocket launched two modules: the Schiaparelli lander and the TGO (Trace Gas Orbiter). The two were delivered to Mars in 226 days, making a journey of 500 million km.
- Schiaparelli was intended to test the technology for future landings. It attempted a landing, but crashed to the surface. TGO's objectives are to detect trace gases in the atmosphere, map water ice distribution below the surface, and conduct high-resolution imaging, including stereo surface imaging.
- The favorable launch windows for Mars trajectories happen once in about two years, and the second phase of the ExoMars mission is scheduled for 2020. A new lander will deploy a rover to navigate autonomously across the Martian surface, transmitting the data it collects via TGO. The main objective of the ExoMars mission is to explore whether life ever existed on Mars.
Figure 67: Three observation modes of the Trace Gas Orbiter: the so-called solar occultation measurements (top right) of light passing through the Martian atmosphere and nadir, or “straight-down,” measurements of reflected sunlight and Mars’ own radiation from its dayside (left) and nightside (right), image credit: IKI, MIPT, Research Team
- The TGO satellite carries four scientific instruments: a high-resolution color imaging system, a high-resolution neutron detector, and two spectrometer suites. The epithermal neutron detector and the ACS (Atmospheric Chemistry Suite) were built at the Space Research Institute in Moscow (IKI).
- TGO's primary scientific objective is to study the climate, atmosphere, and surface of Mars. Using its onboard detectors, sensitive enough to spot trace amounts of gases, the orbiter is expected to settle the doubts concerning the presence of atmospheric methane on Mars. This gas was previously detected by Earth-based telescopes and NASA's Curiosity rover.
- The Russian-built ACS (Figure 102) comprises three infrared spectrometers. It is sensitive enough to detect and measure trace amounts of atmospheric gases such as methane, which could be a sign of geological or biological activity on Mars. The spectrometers have a resolving power of 10,000 or more and a broad spectral coverage—from 0.7 to 17 micrometers. With their help, TGO will clarify the role of the major Martian atmospheric constituents—carbon dioxide, water vapor, and aerosols—in the planet's climate.
- The near-infrared (NIR) channel is accommodated by a versatile echelle spectrometer covering the spectral range between 0.7 and 1.6 µm with a resolving power of about 20,000. This device will mainly focus on the measurements of water vapor, aerosols, the dayside airglows of molecular oxygen, and the nightside airglows caused by the photochemical processes in the Martian atmosphere. Observations in the NIR band will be conducted in three primary modes (Figure 68). Namely, the solar occultation measurements of light passing through the Martian atmosphere and the nadir—or "straight-down"—measurements of sunlight reflected by the planet and its own radiation. Limb measurements are also supported.
- The MIR (Mid-Infrared) channel is a cross-dispersion echelle spectrometer dedicated to solar occultation measurements in the 2.2-4.4 µm range. It has a resolving power of more than 50,000. By design, ACS-MIR will make high-sensitivity measurements of trace gas content, including methane and aerosol concentrations, and the deuterium-to-hydrogen ratio. Meeting the key objectives of the ExoMars mission will depend on observations in the mid-infrared band. It is largely this channel that holds promise of a scientific breakthrough.
- "It enables measurements of Martian atmosphere that are hundreds of times more accurate than ever before," says chief engineer Alexander Trokhimovskiy of the IKI/RAS, who led the work on ACS-MIR. "Also, the probe is bound for an orbit that makes fairly frequent solar occultation observations possible."
- MIPT (Moscow Institute of Physics and Technology) has developed data processing algorithms and designed a general circulation model of Martian atmosphere, which is required for planning experiments and interpreting their results," adds Alexander Rodin, the head of the Applied Infrared Spectroscopy Lab at MIPT.
- Known as TIRVIM, the third ACS instrument is a Fourier-transform spectrometer operating in the 1.7-17 µm range with a resolution of 0.2-1.3 /cm. It is responsible for gathering the data on Martian climate: atmospheric temperature profiles, dust content, and surface temperature. Thermal infrared measurements are expected to map temperatures from the surface of the planet all the way up to the altitude of about 60 km. The instrument will also make it possible to estimate the optical depths of Martian dust and clouds with unparalleled precision, providing an opportunity to detect ozone and hydrogen peroxide—two gases fundamental to Martian photochemistry (Figure 68).
- The TIRVIM detector owes the first half of its name to the thermal infrared, or TIR, spectral band, but the three final letters in the acronym honor Vasily Ivanovich Moroz, the founder of Russian infrared spectrometry and long-standing head of the Department of Planetary Physics at the Space Research Institute of the Russian Academy of Sciences.
• October 16, 2017: Diffuse, water-ice clouds, a hazy sky and a light breeze. Such might have read a weather forecast for the Tharsis volcanic region on Mars on 22 November 2016, when this image was taken by the ExoMars TGO (Trace Gas Orbiter). 60)
- Below, 630 km west of the volcano Arsia Mons, the southernmost of the Tharsis volcanoes, outlines of ancient lava flows dominate the surface (Figure 69). The dark streaks are due to the action of wind on the dark-colored basaltic sands, while redder patches are wind blown dust. A handful of small impact craters can also be seen.
- The Trace Gas Orbiter, a joint effort between ESA and Roscosmos, arrived at Mars on 19 October last year. Since March it has been repeatedly surfing in and out of the atmosphere, generating a tiny amount of drag that will steadily pull it into a near-circular 400 km altitude orbit. It is expected to begin its full science operational phase from this orbit in early 2018.
- Prior to this ‘aerobraking’ phase, several test periods were assigned to check the four science instrument suites from orbit and to refine data processing and calibration techniques.
- The false-color composite shown here was made from images taken with the CaSSIS (Color and Stereo Surface Imaging System) in the near-infrared, red and blue channels.
- The image is centered at 131°W / 8.5°S. The ground resolution is 20.35 m/pixel, and the image is about 58 km across. At the time the image was taken, the altitude was 1791 km, yielding a ground track speed of 1.953 km/s.
Figure 69: A cloudy day over volcanic Mars, captured by the ExoMars orbiter. Clouds, most likely of water-ice, and atmospheric haze in the sky are colored blue/white in this image (image credit: ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO)
• May 24, 2017: The inquiry into the crash-landing of the ExoMars Schiaparelli module has concluded, that conflicting information in the onboard computer caused the descent sequence to end prematurely. 61)
- The Schiaparelli entry, descent and landing demonstrator module separated from its mothership, the TGO (Trace Gas Orbiter), as planned on 16 October last year, and coasted towards Mars for three days.
- Much of the six-minute descent on 19 October 2016 went as expected: the module entered the atmosphere correctly, with the heatshield protecting it at supersonic speeds. Sensors on the front and back shields collected useful scientific and engineering data on the atmosphere and heatshield.
Figure 70: Schiaparelli’s heatshield was equipped with a variety of sensors designed to take measurements as the module entered the atmosphere. The COMARS+ (Combined Aerothermal and Radiometer Sensors Instrument Package), used sensors on the back heatshield to measure pressure, temperature and heat flux. System sensors on the front shield were monitored by the data housekeeping system (image credit: ESA/ATG medialab)
- Telemetry from Schiaparelli was relayed to the main craft, which was entering orbit around the Red Planet at the same time – the first time this had been achieved in Mars exploration. This realtime transmission proved invaluable in reconstructing the unfolding chain of events.
- At the same time as the orbiter recorded Schiaparelli’s transmissions, ESA’s Mars Express orbiter also monitored the lander’s carrier signal, as did the Giant Meterwave Radio Telescope in India.
- In the days and weeks afterwards, NASA’s Mars Reconnaissance Orbiter took a number of images identifying the module, the front shield, and the parachute still connected with the backshield, on Mars, very close to the targeted landing site.
- The images of Figure 71 suggested that these pieces of hardware had separated from the module as expected, although the arrival of Schiaparelli had clearly been at a high speed, with debris strewn around the impact site.
- The independent external inquiry, chaired by ESA’s Inspector General, has now been completed.
- It identifies the circumstances and the root causes, and makes general recommendations to avoid such defects and weaknesses in the future. The report summary can be downloaded here. A summary of the final report is available in PDF. 62)
- Around three minutes after atmospheric entry the parachute deployed, but the module experienced unexpected high rotation rates. This resulted in a brief ‘saturation’ – where the expected measurement range is exceeded – of the Inertial Measurement Unit, which measures the lander’s rotation rate.
- The saturation resulted in a large attitude estimation error by the guidance, navigation and control system software. The incorrect attitude estimate, when combined with the later radar measurements, resulted in the computer calculating that it was below ground level.
Figure 71: Composite of the ExoMars Schiaparelli module elements seen by NASA’s MRO (Mars Reconnaissance Orbiter) HiRISE (High Resolution Imaging Science Experiment) on 1 November 2016. Both the main impact site (top) and the region with the parachute and rear heatshield (bottom left) are now captured in the central portion of the HiRISE imaging swath that is imaged through three different filters, enabling a color image to be constructed. The front heatshield (bottom right) lies outside the central color imaging swath (image credit: NASA/JPL-Caltech/University of Arizona) 63)
Legend to Figure 71: The colors have been graded according to the specific region to best reveal the contrast of features against the martian background. These images are in raw image geometry rather than map-projected, and north is about 7º west of straight up.
- This resulted in the early release of the parachute and back-shell, a brief firing of the thrusters for only 3 sec instead of 30 sec, and the activation of the on-ground system as if Schiaparelli had landed. The surface science package returned one housekeeping data packet before the signal was lost.
- In reality, the module was in free-fall from an altitude of about 3.7 km, resulting in an estimated impact speed of 540 km/h.
- The Schiaparelli Inquiry Board report noted that the module was very close to landing successfully at the planned location and that a very important part of the demonstration objectives were achieved. The flight results revealed required software upgrades, and will help improve computer models of parachute behavior.
- “The realtime relay of data during the descent was crucial to provide this in-depth analysis of Schiaparelli’s fate,” says David Parker, ESA’s Director of Human Spaceflight and Robotic Exploration.
- “We are extremely grateful to the teams of hard-working scientists and engineers who provided the scientific instruments and prepared the investigations on Schiaparelli, and deeply regret that the results were curtailed by the untimely end of the mission. - There were clearly a number of areas that should have been given more attention in the preparation, validation and verification of the entry, descent and landing system. We will take the lessons learned with us as we continue to prepare for the ExoMars 2020 rover and surface platform mission. Landing on Mars is an unforgiving challenge but one that we must meet to achieve our ultimate goals.”
- “Interestingly, had the saturation not occurred and the final stages of landing had been successful, we probably would not have identified the other weak spots that contributed to the mishap,” notes Jan Woerner, ESA's Director General. “As a direct result of this inquiry we have discovered the areas that require particular attention that will benefit the 2020 mission.”
- ExoMars 2020 (Figure 72) has since passed an important review confirming it is on track to meet the launch window. Having been fully briefed on the status of the project, ESA Member States at the Human Spaceflight, Microgravity and Exploration Program Board reconfirmed their commitment to the mission, which includes the first Mars rover dedicated to drilling below the surface to search for evidence of life on the Red Planet.
- Meanwhile the Trace Gas Orbiter has begun its year-long aerobraking in the fringes of the atmosphere that will deliver it to its science orbit in early 2018. The spacecraft has already shown its scientific instruments are ready for work in two observing opportunities in November and March.
- In addition to its main goal of analyzing the atmosphere for gases that may be related to biological or geological activity, the orbiter will also act as a relay for the 2020 rover and surface platform. — The ExoMars program is a joint endeavor between ESA and Roscosmos.
• March 28, 2017: Two ancient sites on Mars that hosted an abundance of water in the planet’s early history have been recommended as the final candidates for the landing site of the 2020 ExoMars rover and surface science platform: Oxia Planum and Mawrth Vallis. 64)
- A primary technical constraint is that the landing site be at a suitably low level, so that there is sufficient atmosphere to help slow the landing module’s parachute descent. Then, the 120 x 19 km landing ellipse should not contain features that could endanger the landing, the deployment of the surface platform ramps for the rover to exit, and driving of the rover. This means scrutinizing the region for steep slopes, loose material and large rocks.
- Oxia Planum was selected in 2015 for further detailed evaluation. Although not yet complete, the investigation so far indicates that the region would meet the various constraints. In addition, one other site had to be chosen from Aram Dorsum and Mawrth Vallis.
- After a two-day meeting with experts from the Mars science community, industry, and ExoMars project, during which the scientific merits of the three sites were presented alongside the preliminary compliance status with the engineering constraints, it was concluded that Mawrth Vallis will be the second site to be evaluated in more detail.
- Around a year before launch, the final decision will be taken on which site will become the ExoMars 2020 landing target.
- All of the sites lie just north of the equator, in a region with many channels cutting through from the southern highlands to the northern highlands. As such, they preserve a rich record of geological history from the planet’s wetter past billions of years ago, and are prime targets for missions like ExoMars that are searching for signatures of past life on Mars.
- Oxia Planum lies at a boundary where many channels emptied into the vast lowland plains and exhibits layers of clay-rich minerals that were formed in wet conditions some 3.9 billion years ago.
- Observations from orbit show that the minerals in Oxia Planum are representative of those found in a wide area around this region, and so would provide insight into the conditions experienced at a global scale during this epoch of martian history.
- Mawrth Vallis is a large outflow channel a few hundred kilometers away from Oxia Planum. The proposed landing ellipse is just to the south of the channel. The entire region exhibits extensively layered, clay-rich sedimentary deposits, and a diversity of minerals that suggests a sustained presence of water over a period of several hundred million years, perhaps including localized ponds.
- In addition, light-toned fractures containing ‘veins’ of water-altered minerals point to interactions between rocks and liquid in subsurface aquifers, and possible hydrothermal activity that may have been beneficial to any ancient life forms.
- Mawrth Vallis offers a window into a large period of martian history that could probe the early evolution of the planet’s environment over time. “While all three sites under discussion would give us excellent opportunities to look for signatures of ancient biomarkers and gain new insights into the planet’s wetter past, we can only carry two sites forward for further detailed analysis,” says Jorge Vago, ESA’s ExoMars rover project scientist. "Thus, after an intense meeting, which focused primarily on the scientific merits of the sites, the Landing Site Selection Working Group has recommended that Mawrth Vallis join Oxia Planum as one of the final two candidates for the ExoMars 2020 mission. Both candidate sites would explore a period of ancient martian history that hasn’t been studied by previous missions.”
Legend to Figure 73:
One example of how the Oxia Planum landing site under consideration for
the ExoMars 2020 mission is being analyzed. The map outlines a boundary
(red) that encapsulates the range of possible 120 x 19 km landing
ellipses, with some added margin. Elevation contours are also
indicated. The colors represent the variety of surface terrains
identified, including plains (green shades), channels (blues), impact
craters (yellow, with black outlines), and wind-blown features (pink).
It is not a geological map intended for scientific analysis, but rather
a tool used to identify different surface textures and where potential
hazards may lie.
Figure 74: Mawrth Vallis martian mosaic (image credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO)
Legend to Figure 74: Sculpted by ancient water flowing on the surface, Mawrth Vallis is one of the most remarkable outflow channels on Mars. The valley, once a potentially habitable place, is one of the main features of a region at the boundary between the southern highlands and the northern lowlands.
Mawrth Vallis takes center stage in this image, a bird’s eye view of a 330,000 km2 area surrounding the valley. With a length of 600 km and a depth of up to 2 km, it is one of the biggest valleys on Mars. Huge amounts of water once passed through it, from a higher elevation region, part of which is shown in the lower right of the image, into the northern plains, in the top left.
Among the remarkable features are the large exposures of light-toned phyllosilicates (weathered clay minerals) that lie along its course. Phyllosilicates on Mars are evidence of the past presence of liquid water and point to the possibility that habitable environments could have existed on the planet up until 3.6 billion years ago.
A dark cap rock, remains of ancient volcanic ash, covers many of the clays and could have protected traces of ancient microbes in the rocks from radiation and erosion. This makes Mawrth Vallis one of the most interesting regions for geologists and astrobiologists alike. It is one of the candidate landing sites for ExoMars 2020, a joint mission between ESA and Russia, with the primary goal of finding out if life once existed on Mars.
The name comes from the Welsh word for Mars (“Mawrth”) and the Latin for valley (“Vallis”). This mosaic was created using nine individual images taken by the high-resolution stereo camera on ESA’s Mars Express spacecraft, which has been orbiting Mars since late 2003. It is one of a set of images of this region previously published on 7 July 2016 on the DLR website and the homepage of the Freie Universität Berlin.