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NASA: Life Signs Could Survive Near Surfaces of Enceladus and Europa


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NASA: Life Signs Could Survive Near Surfaces of Enceladus and Europa

Europa, a moon of Jupiter, and Enceladus, a moon of Saturn, have evidence of oceans beneath their ice crusts. A NASA experiment suggests that if these oceans support life, signatures of that life in the form of organic molecules (e.g. amino acids, nucleic acids, etc.) could survive just under the surface ice despite the harsh radiation on these worlds. If robotic landers are sent to these moons to look for life signs, they would not have to dig very deep to find amino acids that have survived being altered or destroyed by radiation.

“Based on our experiments, the ‘safe’ sampling depth for amino acids on Europa is almost 8 inches (around 20 centimeters) at high latitudes of the trailing hemisphere (hemisphere opposite to the direction of Europa’s motion around Jupiter) in the area where the surface hasn’t been disturbed much by meteorite impacts,” said Alexander Pavlov of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, lead author of a paper on the research published July 18 in Astrobiology. “Subsurface sampling is not required for the detection of amino acids on Enceladus – these molecules will survive radiolysis (breakdown by radiation) at any location on the Enceladus surface less than a tenth of an inch (under a few millimeters) from the surface.”

The frigid surfaces of these nearly airless moons are likely uninhabitable due to radiation from both high-speed particles trapped in their host planet’s magnetic fields and powerful events in deep space, such as exploding stars. However, both have oceans under their icy surfaces that are heated by tides from the gravitational pull of the host planet and neighboring moons. These subsurface oceans could harbor life if they have other necessities, such as an energy supply as well as elements and compounds used in biological molecules.

Fountains of ice erupt from the surface of Enceladus. The small moon is mostly in shadow, which makes the geysers illuminated by sunlight stand out.
Dramatic plumes, both large and small, spray water ice and vapor from many locations along the famed “tiger stripes” near the south pole of Saturn’s moon Enceladus.
NASA/JPL/Space Science Institute

The research team used amino acids in radiolysis experiments as possible representatives of biomolecules on icy moons. Amino acids can be created by life or by non-biological chemistry. However, finding certain kinds of amino acids on Europa or Enceladus would be a potential sign of life because they are used by terrestrial life as a component to build proteins. Proteins are essential to life as they are used to make enzymes which speed up or regulate chemical reactions and to make structures. Amino acids and other compounds from subsurface oceans could be brought to the surface by geyser activity or the slow churning motion of the ice crust.

Europa has reddish brown lines and patches in this image from Juno.
This view of Jupiter’s icy moon Europa was captured by JunoCam, the public engagement camera aboard NASA’s Juno spacecraft, during the mission’s close flyby on Sept. 29, 2022. The picture is a composite of JunoCam’s second, third, and fourth images taken during the flyby, as seen from the perspective of the fourth image. North is to the left.

The images have a resolution of just over 0.5 to 2.5 miles per pixel (1 to 4 kilometers per pixel).

As with our Moon and Earth, one side of Europa always faces Jupiter, and that is the side of Europa visible here. Europa’s surface is crisscrossed by fractures, ridges, and bands, which have erased terrain older than about 90 million years.

Citizen scientist Kevin M. Gill processed the images to enhance the color and contrast.

NASA/JPL-Caltech/SwRI/MSSS Image processing: Kevin M. Gill CC BY 3.0

To evaluate the survival of amino acids on these worlds, the team mixed samples of amino acids with ice chilled to about minus 321 Fahrenheit (-196 Celsius) in sealed, airless vials and bombarded them with gamma-rays, a type of high-energy light, at various doses. Since the oceans might host microscopic life, they also tested the survival of amino acids in dead bacteria in ice. Finally, they tested samples of amino acids in ice mixed with silicate dust to consider the potential mixing of material from meteorites or the interior with surface ice.

Image showing samples loaded in a dewar before being chilled with liquid nitrogen.
This image shows experiment samples loaded in the specially designed dewar which will be filled with liquid nitrogen shortly after and placed under gamma radiation. Notice that the flame-sealed test tubes are wrapped in cotton fabric to keep them together because test tubes become buoyant in liquid nitrogen and start floating around in the dewar, interfering with the proper radiation exposure.
Candace Davison

The experiments provided pivotal data to determine the rates at which amino acids break down, called radiolysis constants. With these, the team used the age of the ice surface and the radiation environment at Europa and Enceladus to calculate the drilling depth and locations where 10 percent of the amino acids would survive radiolytic destruction.

Although experiments to test the survival of amino acids in ice have been done before, this is the first to use lower radiation doses that don’t completely break apart the amino acids, since just altering or degrading them is enough to make it impossible to determine if they are potential signs of life. This is also the first experiment using Europa/Enceladus conditions to evaluate the survival of these compounds in microorganisms and the first to test the survival of amino acids mixed with dust.

The team found that amino acids degraded faster when mixed with dust but slower when coming from microorganisms.

“Slow rates of amino acid destruction in biological samples under Europa and Enceladus-like surface conditions bolster the case for future life-detection measurements by Europa and Enceladus lander missions,” said Pavlov. “Our results indicate that the rates of potential organic biomolecules’ degradation in silica-rich regions on both Europa and Enceladus are higher than in pure ice and, thus, possible future missions to Europa and Enceladus should be cautious in sampling silica-rich locations on both icy moons.”

A potential explanation for why amino acids survived longer in bacteria involves the ways ionizing radiation changes molecules — directly by breaking their chemical bonds or indirectly by creating reactive compounds nearby which then alter or break down the molecule of interest. It’s possible that bacterial cellular material protected amino acids from the reactive compounds produced by the radiation.

The research was supported by NASA under award number 80GSFC21M0002, NASA’s Planetary Science Division Internal Scientist Funding Program through the Fundamental Laboratory Research work package at Goddard, and NASA Astrobiology NfoLD award 80NSSC18K1140.

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Jul 18, 2024
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      Gravity slowly pulls the heaviest elements to a planet’s center over time, which is how Earth ended up with a dense core of liquid iron. While Vesta has long been considered a differentiated asteroid, a more homogenous structure would suggest that it may not have fully formed layers or may have formed from the debris of another planetary body after a massive impact.
      In 2016, Park used the same data types as the Vesta study to focus on Dawn’s second target, the dwarf planet Ceres, and results suggested a partially differentiated interior.
      Park and his team recently applied a similar technique to Jupiter’s volcanic moon Io, using data acquired by NASA’s Juno and Galileo spacecraft during their flybys of the Jovian satellite as well as from ground-based observations. By measuring how Io’s gravity changes as it orbits Jupiter, which exerts a powerful tidal force, they revealed that the fiery moon is unlikely to possess a global magma ocean.
      “Our technique isn’t restricted just to Io, Ceres, Vesta, or the Moon,” said Park. “There are many opportunities in the future to apply our technique for studying the interiors of intriguing planetary bodies throughout the solar system.”
      News Media Contacts
      Ian J. O’Neill
      Jet Propulsion Laboratory, Pasadena, Calif.
      818-354-2649
      ian.j.oneill@jpl.nasa.gov
      Karen Fox / Molly Wasser
      NASA Headquarters, Washington
      202-358-1600
      karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov
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      Last Updated May 14, 2025 Related Terms
      Vesta Dawn Earth's Moon GRAIL (Gravity Recovery And Interior Laboratory) Jet Propulsion Laboratory Planetary Science Small Bodies of the Solar System The Solar System Explore More
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      Explore Webb Webb News Latest News Latest Images Webb’s Blog Awards X (offsite – login reqd) Instagram (offsite – login reqd) Facebook (offsite- login reqd) Youtube (offsite) Overview About Who is James Webb? Fact Sheet Impacts+Benefits FAQ Science Overview and Goals Early Universe Galaxies Over Time Star Lifecycle Other Worlds Observatory Overview Launch Deployment Orbit Mirrors Sunshield Instrument: NIRCam Instrument: MIRI Instrument: NIRSpec Instrument: FGS/NIRISS Optical Telescope Element Backplane Spacecraft Bus Instrument Module Multimedia About Webb Images Images Videos What is Webb Observing? 3d Webb in 3d Solar System Podcasts Webb Image Sonifications Team International Team People Of Webb More For the Media For Scientists For Educators For Fun/Learning 5 Min Read Another First: NASA Webb Identifies Frozen Water in Young Star System
      For the first time, researchers confirmed the presence of crystalline water ice in a dusty debris disk that orbits a Sun-like star, using NASA’s James Webb Space Telescope. The full artist’s concept illustration and full caption is shown below. Credits:
      NASA, ESA, CSA, Ralf Crawford (STScI) Is frozen water scattered in systems around other stars? Astronomers have long expected it is, partially based on previous detections of its gaseous form, water vapor, and its presence in our own solar system.
      Now there is definitive evidence: Researchers confirmed the presence of crystalline water ice in a dusty debris disk that orbits a Sun-like star 155 light-years away using detailed data known as spectra from NASA’s James Webb Space Telescope. (The term water ice specifies its makeup, since many other frozen molecules are also observed in space, such as carbon dioxide ice, or “dry ice.”) In 2008, data from NASA’s retired Spitzer Space Telescope hinted at the possibility of frozen water in this system.
      “Webb unambiguously detected not just water ice, but crystalline water ice, which is also found in locations like Saturn’s rings and icy bodies in our solar system’s Kuiper Belt,” said Chen Xie, the lead author of the new paper and an assistant research scientist at Johns Hopkins University in Baltimore, Maryland.
      All the frozen water Webb detected is paired with fine dust particles throughout the disk — like itsy-bitsy “dirty snowballs.” The results published Wednesday in the journal Nature.
      Astronomers have been waiting for this definitive data for decades. “When I was a graduate student 25 years ago, my advisor told me there should be ice in debris disks, but prior to Webb, we didn’t have instruments sensitive enough to make these observations,” said Christine Chen, a co-author and associate astronomer at the Space Telescope Science Institute in Baltimore. “What’s most striking is that this data looks similar to the telescope’s other recent observations of Kuiper Belt objects in our own solar system.”
      Water ice is a vital ingredient in disks around young stars — it heavily influences the formation of giant planets and may also be delivered by small bodies like comets and asteroids to fully formed rocky planets. Now that researchers have detected water ice with Webb, they have opened the door for all researchers to study how these processes play out in new ways in many other planetary systems.
      Image: Debris Disk Around Star HD 181327 (Artist’s Concept)
      For the first time, researchers confirmed the presence of crystalline water ice in a dusty debris disk that orbits a Sun-like star, using NASA’s James Webb Space Telescope. All the frozen water detected by Webb is paired with fine dust particles throughout the disk. The majority of the water ice observed is found where it’s coldest and farthest from the star. The closer to the star the researchers looked, the less water ice they found. NASA, ESA, CSA, Ralf Crawford (STScI) Rocks, Dust, Ice Rushing Around
      The star, cataloged HD 181327, is significantly younger than our Sun. It’s estimated to be 23 million years old, compared to the Sun’s more mature 4.6 billion years. The star is slightly more massive than the Sun, and it’s hotter, which led to the formation of a slightly larger system around it.
      Webb’s observations confirm a significant gap between the star and its debris disk — a wide area that is free of dust. Farther out, its debris disk is similar to our solar system’s Kuiper Belt, where dwarf planets, comets, and other bits of ice and rock are found (and sometimes collide with one another). Billions of years ago, our Kuiper Belt was likely similar to this star’s debris disk.
      “HD 181327 is a very active system,” Chen said. “There are regular, ongoing collisions in its debris disk. When those icy bodies collide, they release tiny particles of dusty water ice that are perfectly sized for Webb to detect.”
      Frozen Water — Almost Everywhere
      Water ice isn’t spread evenly throughout this system. The majority is found where it’s coldest and farthest from the star. “The outer area of the debris disk consists of over 20% water ice,” Xie said.
      The closer in the researchers looked, the less water ice they found. Toward the middle of the debris disk, Webb detected about 8% water ice. Here, it’s likely that frozen water particles are produced slightly faster than they are destroyed. In the area of the debris disk closest to the star, Webb detected almost none. It’s likely that the star’s ultraviolet light vaporizes the closest specks of water ice. It’s also possible that rocks known as planetesimals have “locked up” frozen water in their interiors, which Webb can’t detect.
      This team and many more researchers will continue to search for — and study — water ice in debris disks and actively forming planetary systems throughout our Milky Way galaxy. “The presence of water ice helps facilitate planet formation,” Xie said. “Icy materials may also ultimately be ‘delivered’ to terrestrial planets that may form over a couple hundred million years in systems like this.”
      The researchers observed HD 181327 with Webb’s NIRSpec (Near-Infrared Spectrograph), which is super-sensitive to extremely faint dust particles that can only be detected from space.
      The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).
      To learn more about Webb, visit:
      https://science.nasa.gov/webb
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      View/Download all image products at all resolutions for this article from the Space Telescope Science Institute.
      View/Download the research results from the journal Nature.
      Media Contacts
      Laura Betz – laura.e.betz@nasa.gov
      NASA’s Goddard Space Flight Center, Greenbelt, Md.
      Claire Blome – cblome@stsci.edu
      Space Telescope Science Institute, Baltimore, Md.
      Christine Pulliam – cpulliam@stsci.edu
      Space Telescope Science Institute, Baltimore, Md.
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      Last Updated May 14, 2025 Editor Marty McCoy Contact Laura Betz laura.e.betz@nasa.gov Related Terms
      James Webb Space Telescope (JWST) Astrophysics Goddard Space Flight Center Science & Research Stars The Universe View the full article
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