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Europa Clipper Mission to Jupiter's Icy Moon

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NASA's Europa Clipper will conduct detailed reconnaissance of Jupiter's moon Europa and investigate whether the icy moon could harbor conditions suitable for life.

An icy ocean world in our solar system that could tell us more about the potential for life on other worlds is coming into focus with confirmation of the Europa Clipper mission’s next phase. The decision allows the mission to progress to completion of final design, followed by the construction and testing of the entire spacecraft and science payload. 1)

“We are all excited about the decision that moves the Europa Clipper mission one key step closer to unlocking the mysteries of this ocean world,” said Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington. “We are building upon the scientific insights received from the flagship Galileo and Cassini spacecraft and working to advance our understanding of our cosmic origin, and even life elsewhere.”

The mission will conduct an in-depth exploration of Jupiter's moon, Europa, and investigate whether the icy moon could harbor conditions suitable for life, honing our insights into astrobiology. To develop this mission in the most cost-effective fashion, NASA is targeting to have the Europa Clipper spacecraft complete and ready for launch as early as 2023. The agency baseline commitment, however, supports a launch readiness date by 2025.

NASA's Jet Propulsion Laboratory in Pasadena, California leads the development of the Europa Clipper mission in partnership with the Johns Hopkins University Applied Physics Laboratory for the Science Mission Directorate. Europa Clipper is managed by the Planetary Missions Program Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama.

Forty years ago, a Voyager spacecraft snapped the first closeup images of Europa, one of Jupiter’s 79 moons. These revealed brownish cracks slicing the moon’s icy surface, which give Europa the look of a veiny eyeball. Missions to the outer solar system in the decades since have amassed enough additional information about Europa to make it a high-priority target of investigation in NASA’s search for life (Figure 2). 2)

What makes this moon so alluring is the possibility that it may possess all of the ingredients necessary for life. Scientists have evidence that one of these ingredients, liquid water, is present under the icy surface and may sometimes erupt into space in huge geysers. But no one has been able to confirm the presence of water in these plumes by directly measuring the water molecule itself. Now, an international research team led out of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, has detected the water vapor for the first time above Europa’s surface. The team measured the vapor by peering at Europa through one of the world’s biggest telescopes in Hawaii.

Confirming that water vapor is present above Europa helps scientists better understand the inner workings of the moon. For example, it helps support an idea, of which scientists are confident, that there’s a liquid water ocean, possibly twice as big as Earth’s, sloshing beneath this moon’s miles-thick ice shell. Another source of water for the plumes, some scientists suspect, could be shallow reservoirs of melted water ice not far below Europa’s surface. It’s also possible that Jupiter’s strong radiation field is stripping water particles from Europa’s ice shell, though the recent investigation argued against this mechanism as the source of the observed water.

“Essential chemical elements (carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur) and sources of energy, two of three requirements for life, are found all over the solar system. But the third — liquid water — is somewhat hard to find beyond Earth,” said Lucas Paganini, a NASA planetary scientist who led the water detection investigation. “While scientists have not yet detected liquid water directly, we’ve found the next best thing: water in vapor form.”

Paganini and his team reported in the journal Nature Astronomy on November 18 that they detected enough water releasing from Europa (5,202 pounds, or 2,360 kilograms, per second) to fill an Olympic-size swimming pool within minutes. Yet, the scientists also found that the water appears infrequently, at least in amounts large enough to detect from Earth, said Paganini: “For me, the interesting thing about this work is not only the first direct detection of water above Europa, but also the lack thereof within the limits of our detection method.”

Indeed, Paganini’s team detected the faint yet distinct signal of water vapor just once throughout 17 nights of observations between 2016 and 2017. Looking at the moon from the W. M. Keck Observatory atop the dormant Mauna Kea volcano in Hawaii, the scientists saw water molecules at Europa’s leading hemisphere, or the side of the moon that’s always facing in the direction of the moon’s orbit around Jupiter. (Europa, like Earth’s moon, is gravitationally locked to its host planet, so the leading hemisphere always faces the direction of the orbit, while the trailing hemisphere always faces in the opposite direction.)


Figure 1: Artist's rendition of Europa Clipper's mission to Jupiter's Icy Moon (image credit: NASA)


Figure 2: Left: A view of Europa taken from 2.9 million km away on March 2, 1979 by the Voyager 1 spacecraft. Center: A color image of Europa taken by the Voyager 2 spacecraft during its close encounter on July 9, 1979. Right: A view of Europa made from images taken by the Galileo spacecraft in the late 1990s (image credit: NASA/JPL)

They used a spectrograph at the Keck Observatory that measures the chemical composition of planetary atmospheres through the infrared light they emit or absorb. Molecules such as water emit specific frequencies of infrared light as they interact with solar radiation.

Mounting Evidence for Water

Before the recent water vapor detection, there have been many tantalizing findings on Europa. The first came from NASA’s Galileo spacecraft, which measured perturbations in Jupiter’s magnetic field near Europa while orbiting the gas giant planet between 1995 and 2003. The measurements suggested to scientists that electrically conductive fluid, likely a salty ocean beneath Europa’s ice layer, was causing the magnetic disturbances. When researchers analyzed the magnetic disturbances more closely in 2018, they found evidence of possible plumes.

In the meantime, scientists announced in 2013 that they had used NASA’s Hubble Space Telescope to detect the chemical elements hydrogen (H) and oxygen (O) — components of water (H2O) — in plume-like configurations in Europa’s atmosphere. And a few years later, other scientists used Hubble to gather more evidence of possible plume eruptions when they snapped photos of finger-like projections that appeared in silhouette as the moon passed in front of Jupiter.

“This first direct identification of water vapor on Europa is a critical confirmation of our original detections of atomic species, and it highlights the apparent sparsity of large plumes on this icy world” said Lorenz Roth, an astronomer and physicist from KTH Royal Institute of Technology in Stockholm who led the 2013 Hubble study and was a co-author of this recent investigation.

Roth’s research, along with other previous Europa findings, have only measured components of water above the surface. The trouble is that detecting water vapor at other worlds is challenging. Existing spacecraft have limited capabilities to detect it, and scientists using ground-based telescopes to look for water in deep space have to account for the distorting effect of water in Earth’s atmosphere. To minimize this effect, Paganini’s team used complex mathematical and computer modeling to simulate the conditions of Earth’s atmosphere so they could differentiate Earth’s atmospheric water from Europa’s in data returned by the Keck spectrograph.

“We performed diligent safety checks to remove possible contaminants in ground-based observations,” said Avi Mandell, a Goddard planetary scientist on Paganini’s team. “But, eventually, we’ll have to get closer to Europa to see what’s really going on.”

Scientists will soon be able get close enough to Europa to settle their lingering questions about the inner and outer workings of this possibly habitable world. The forthcoming Europa Clipper mission, expected to launch in the mid-2020s, will round out half a century of scientific discovery that started with a modest photo of a mysterious, veiny eyeball.

When it arrives at Europa, the Clipper orbiter will conduct a detailed survey of Europa’s surface, deep interior, thin atmosphere, subsurface ocean, and potentially even smaller active vents. Clipper will try to take images of any plumes and sample the molecules it finds in the atmosphere with its mass spectrometers. It will also seek out a fruitful site from which a future Europa lander could collect a sample. These efforts should further unlock the secrets of Europa and its potential for life.

Other Goddard researchers on Paganini’s team included Geronimo Villanueva, Michael Mumma, and Terry Hurford. Kurt Retherford, from Southwest Research Institute, also contributed to the research.

Figure 3: Water Vapor Plumes on Europa. What makes Jupiter's moon Europa so alluring is the possibility that it may possess all the ingredients necessary for life. Scientists have evidence that one of these ingredients, liquid water, is present under the icy surface and may sometimes erupt into space in huge geysers. However, no one has been able to confirm the presence of water in these plumes by direct measurement of the water molecule itself. Now, an international research team led out of NASA's Goddard Space Flight Center in Greenbelt, Maryland has detected the water vapor for the first time above Europa's surface. The team measured the vapor by peering at Europa through one of the world's biggest telescopes in Hawaii. Confirming that water vapor is present above Europa helps scientists better understand the inner workings of the moon (video credit: NASA/GSFC)

Development status

• July 12, 2021: Jupiter’s moon Europa and its global ocean may currently have conditions suitable for life. Scientists are studying processes on the icy surface as they prepare to explore. 3)


Figure 4: This color view of Jupiter’s moon Europa was captured by NASA’s Galileo spacecraft in the late 1990s. Scientists are studying processes that affect the surface as they prepare to explore the icy body (image credit: NASA/JPL-Caltech/SETI Institute)

- It’s easy to see the impact of space debris on our Moon, where the ancient, battered surface is covered with craters and scars. Jupiter’s icy moon Europa withstands a similar trouncing – along with a punch of super-intense radiation. As the uppermost surface of the icy moon churns, material brought to the surface is zapped by high-energy electron radiation accelerated by Jupiter.

- NASA-funded scientists are studying the cumulative effects of small impacts on Europa’s surface as they prepare to explore the distant moon with the Europa Clipper mission and study the possibilities for a future lander mission. Europa is of particular scientific interest because its salty ocean, which lies beneath a thick layer of ice, may currently have conditions suitable for existing life. That water may even make its way into the icy crust and onto the moon’s surface.

- New research and modeling estimate how far down that surface is disturbed by the process called “impact gardening.” The work, published July 12 in Nature Astronomy, estimates that the surface of Europa has been churned by small impacts to an average depth of about 12 inches (30 centimeters) over tens of millions of years. And any molecules that might qualify as potential biosignatures, which include chemical signs of life, could be affected at that depth. 4)


Figure 5: In this zoomed-in image of Europa’s surface, captured by NASA’s Galileo mission, the thin, bright layer, visible atop a cliff in the center shows the kind of areas churned by impact gardening (image credit: NASA/JPL-Caltech)

- That’s because the impacts would churn some material to the surface, where radiation would likely break the bonds of any potential large, delicate molecules generated by biology. Meanwhile, some material on the surface would be pushed downward, where it could mix with the subsurface.

- “If we hope to find pristine, chemical biosignatures, we will have to look below the zone where impacts have been gardening,” said lead author Emily Costello, a planetary research scientist at the University of Hawaii at Manoa. “Chemical biosignatures in areas shallower than that zone may have been exposed to destructive radiation.”

Going Deeper

- While impact gardening has long been understood to be likely taking place on Europa and other airless bodies in the solar system, the new modeling provides the most comprehensive picture yet of the process. In fact, it is the first to take into account secondary impacts caused by debris raining back down onto Europa’s surface after being kicked up by an initial impact. The research makes the case that Europa’s mid- to high-latitudes would be less affected by the double whammy of impact gardening and radiation.

- “This work broadens our understanding of the fundamental processes on surfaces across the solar system,” said Cynthia Phillips, a Europa scientist at NASA’s Jet Propulsion Laboratory in Southern California and a co-author of the study. “If we want to understand the physical characteristics and how planets in general evolve, we need to understand the role impact gardening has in reshaping them.”

- Managed by JPL for NASA, Europa Clipper will help develop that understanding. The spacecraft, targeting a 2024 launch, will conduct a series of close flybys of Europa as it orbits Jupiter. It will carry instruments to thoroughly survey the moon, as well as sample the dust and gases that are kicked up above the surface.

• May 25, 2021: Jupiter’s moon Europa has an icy crust covering a vast, global ocean. The rocky layer underneath may be hot enough to melt, leading to undersea volcanoes. 5)

- New research and computer modeling show that volcanic activity may have occurred on the seafloor of Jupiter’s moon Europa in the recent past – and may still be happening. NASA’s upcoming Europa Clipper mission, targeting a 2024 launch, will swoop close to the icy moon and collect measurements that may shed light on the recent findings.

- Scientists have strong evidence that Europa harbors an enormous ocean between its icy crust and rocky interior. The new work shows how the moon may have enough internal heat to partially melt this rocky layer, a process that could feed volcanoes on the ocean floor. The recent 3D modeling of how this internal heat is produced and transferred is the most detailed and thorough examination yet of the effect this interior heating has on the moon.

- The key to Europa’s rocky mantle being hot enough to melt lies with the massive gravitational pull Jupiter has on its moons. As Europa revolves around the gas giant, the icy moon’s interior flexes. The flexing forces energy into the moon’s interior, which then seeps out as heat (think of how repeatedly bending a paperclip generates heat). The more the moon’s interior flexes, the more heat is generated.

- The research, published recently in Geophysical Research Letters, models in detail how Europa’s rocky part may flex and heat under the pull of Jupiter’s gravity. It shows where heat dissipates and how it melts that rocky mantle, increasing the likelihood of volcanoes on the seafloor.

- Volcanic activity on Europa has been a topic of speculation for decades. By comparison, Jupiter’s moon Io is obviously volcanic. Hundreds of volcanoes there erupt lava fountains and eject volcanic gas and dust up to 250 miles (400 km) high – activity that is due to the same kind of internal heating caused by Jupiter’s pull. But Europa is farther away than Io is from its host planet, so scientists have wondered whether the effect would be similar under the icy surface.


Figure 6: Scientists’ findings suggest that the interior of Jupiter’s moon Europa may consist of an iron core, surrounded by a rocky mantle in direct contact with an ocean under the icy crust. New research models how internal heat may fuel volcanoes on the seafloor (image credit: NASA/JPL-Caltech/Michael Carroll)

- Led by Marie Běhounková of Charles University in the Czech Republic, the authors further predicted that volcanic activity is most likely to occur near Europa’s poles – the latitudes where the most heat is generated. They also looked at how volcanic activity may have evolved over time. Long-lived energy sources give more opportunity for potential life to have developed.

- Underwater volcanoes, if present, could power hydrothermal systems like those that fuel life at the bottom of Earth’s oceans. On Earth, when seawater comes into contact with hot magma, the interaction results in chemical energy. And it is chemical energy from these hydrothermal systems, rather than from sunlight, that helps support life deep in our own oceans. Volcanic activity on Europa’s seafloor would be one way to support a potential habitable environment in that moon’s ocean.

- “Our findings provide additional evidence that Europa’s subsurface ocean may be an environment suitable for the emergence of life,” Běhounková said. “Europa is one of the rare planetary bodies that might have maintained volcanic activity over billions of years, and possibly the only one beyond Earth that has large water reservoirs and a long-lived source of energy.”

Direct Observations

- NASA scientists will have the opportunity to put the new predictions to the test when Europa Clipper reaches its target in 2030. The spacecraft will orbit Jupiter and perform dozens of close flybys of Europa to map the moon and investigate its composition. Among the science data it collects, the spacecraft will survey the surface in detail and sample the moon’s thin atmosphere.

- The surface and atmosphere observations will give scientists a chance to learn more about the moon’s interior ocean if the water percolates up through the icy crust. Scientists believe the exchange of material between the ocean and the crust would leave traces of seawater on the surface. They also believe the exchange may emit gas, and possibly even plumes of water vapor, with ejected particles that could contain materials coming from the seafloor.

- As Europa Clipper measures the moon’s gravity and magnetic field, anomalies in those areas, especially toward the poles, could help confirm the volcanic activity predicted by the new research.

- “The prospect for a hot, rocky interior and volcanoes on Europa’s seafloor increases the chance that Europa’s ocean could be a habitable environment,” said Europa Clipper Project Scientist Robert Pappalardo of NASA’s Jet Propulsion Laboratory in Southern California. “We may be able to test this with Europa Clipper’s planned gravity and compositional measurements, which is an exciting prospect.”

More about the Mission

- Missions such as Europa Clipper help contribute to the field of astrobiology, the interdisciplinary research on the variables and conditions of distant worlds that could harbor life as we know it. While Europa Clipper is not a life-detection mission, it will conduct detailed reconnaissance of Europa and investigate whether the icy moon, with its subsurface ocean, has the capability to support life. Understanding Europa’s habitability will help scientists better understand how life developed on Earth and the potential for finding life beyond our planet.

- Managed by Caltech in Pasadena, California, JPL leads the development of the Europa Clipper mission in partnership with the Johns Hopkins Applied Physics Lab (APL) in Maryland for the agency’s Science Mission Directorate in Washington. The Planetary Missions Program Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama, executes program management of the Europa Clipper mission.

• February 10, 2021: NASA is no longer considering launching the Europa Clipper mission on the Space Launch System, deciding instead to launch the spacecraft on a commercial rocket it will procure in the next year. 6)

• January 29, 2021: NASA has issued a request for information for launch services for its Europa Clipper mission, a sign the agency is taking advantage of language in a recent appropriations bill that allows it to consider alternatives to the Space Launch System. 7)

- The Jan. 26 request for information seeks data from companies that believe they have vehicles that can launch the mission, which will go into orbit around Jupiter and make dozens of close approaches to Europa, an icy, potentially habitable moon.

- The launch vehicle would have to be able to launch the spacecraft, weighing at least 6,065 kilograms, on a trajectory that would incorporate gravity-assist flybys of Mars and Earth before arriving at Jupiter. The launch would take place during a three-week window in October 2024.

- At a July 2020 briefing to a National Academies committee, Europa Clipper project officials presented a proposal for once such trajectory. A launch in October 2024 would be followed by flybys of Mars in February 2025 and of Earth in December 2026, with the spacecraft entering orbit around Jupiter in April 2030. NASA’s Launch Services Program, the briefing stated, had determined that trajectory using a “commercial option” for a launch vehicle was feasible.

- The SLS had been the preferred vehicle for the Europa Clipper mission because it could get the spacecraft to Jupiter much more quickly. The same briefing described a launch window in August 2024 that, using SLS, would get the spacecraft to Jupiter in no more than three years, without the need for flybys.

- NASA, in recent budget proposals, sought to launch Europa Clipper on a commercial vehicle rather than SLS. It argued that doing so would save the agency as much as $1.5 billion and free up SLS vehicles for use in the Artemis program of human lunar exploration. Congress, though, mandated the use of SLS for Europa Clipper in appropriations bills through fiscal year 2020.

- Another factor in the launch vehicle debate emerged in August, when NASA disclosed it was investigating “potential hardware compatibility issues” between SLS and Europa Clipper. The agency didn’t elaborate on the specific issues, believed to be associated with vibrations and other environmental factors the spacecraft would experience during launch.

- Congress, in the fiscal year 2021 omnibus spending bill passed last month, gave NASA some flexibility regarding the launch of Europa Clipper. The bill again directed the use of SLS for the mission, but only if “the SLS is available and if torsional loading analysis has confirmed Clipper’s appropriateness for SLS.” The latter condition refers to the hardware compatibility issues previously reported by NASA.

- The most likely commercial option for launching Europa Clipper is SpaceX’s Falcon Heavy. United Launch Alliance’s Delta 4 Heavy, an earlier option, is no longer available since the remaining vehicles have all been assigned to national security launches. ULA plans to retire the vehicle by the middle of the decade as it transitions to the Vulcan Centaur.

- Both Vulcan Centaur and Blue Origin’s New Glenn could be alternatives, but neither vehicle has made its first flight. The request for information states that the vehicle for Europa Clipper must meet NASA’s Category 3 requirements for launch services, which requires a vehicle have at least three successful launches, including at least two consecutive successful launches. Falcon Heavy has flown three times so far, all successfully.

- The appropriations bill that gave NASA the option to consider alternatives to SLS did direct the agency to conduct a “full and open competition” for launch services if it chose not to use SLS, including allowing vehicles that are not currently on its NASA Launch Services 2 contract.

- Responses to the request for information are due to NASA by Feb. 8. NASA hasn’t stated when it will decide on how to launch Europa Clipper, or issue a formal request for proposals for launch services, but agency officials said last summer they had hoped to decide how they would launch the mission by the end of 2020.

1) ”Europa Clipper's Mission to Jupiter’s Icy Moon Confirmed,” NASA, 19 August 2019, URL:

2) NASA Scientists Confirm Water Vapor on Europa,” NASA, 18 November 2019, URL:

3) ”Surface of Jupiter’s Moon Europa Churned by Small Impacts,” NASA/JPL News, 12 July 2021, URL:

4) E. S. Costello, C. B. Phillips, P. G. Lucey & R. R. Ghent, ”Impact gardening on Europa and repercussions for possible biosignatures,” Nature Astronomy, Published: 12 July 2021,

5) ”Europa’s Interior May Be Hot Enough to Fuel Seafloor Volcanoes,” NASA/JPL News, 25 May 2021, URL:

6) Jeff Foust, ”NASA to use commercial launch vehicle for Europa Clipper,” SpaceNews, 10 February 2021, URL:

7) Jeff Foust, ”NASA seeks input on Europa Clipper launch options,” SpaceNews, 29 January, 2021, URL:

The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (

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