Signs of life may survive near the surfaces of Enceladus and Europa

NASA Researchers have found that Amino acidswhich are potential signs of life, may survive near the surface. Europe Enceladus, moons Jupiter And Saturn respectively.

Experiments suggest that these organic molecules can withstand radiation just beneath the ice, making them accessible to future robotic vehicles without the need for deep drilling.

Exploring the potential for life on icy moons

Jupiter’s moon Europa and Saturn’s moon Enceladus both hold evidence of oceans beneath their icy crusts. A NASA experiment suggests that if these oceans support life, signs of that life in the form of organic molecules (such as amino acids, nucleic acids, etc.) might survive just beneath the surface ice despite the intense radiation on these worlds. If robotic landers were sent to these moons to search for signs of life, there would be no need to dig deep to find amino acids that have survived being changed or destroyed by radiation.

“Based on our experiments, the ‘safe’ sampling depth for amino acids on Europa is about 8 inches (about 20 centimeters) at the high latitudes of the trailing hemisphere (the hemisphere opposite to the direction of Europa’s motion around Jupiter) in a region where the surface has not 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 the journal Astrobiology“Detecting amino acids on Enceladus does not require sampling the interior of the Earth, as these molecules would survive radioactive decay anywhere on Enceladus less than a tenth of an inch (less than a few millimeters) from the surface.”

Large and small plumes of water ice and vapor billow from several locations along the famous “tiger stripes” near the south pole of Saturn’s moon Enceladus. Image credit: NASA/JPL/Space Science Institute

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

Experimental approach and results

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

This image of Jupiter’s icy moon Europa was captured by JunoCam, the public outreach camera on NASA’s Juno spacecraft, during the mission’s close flyby on Sept. 29, 2022. The image is a composite of the second, third, and fourth images taken by JunoCam during the close flyby, as seen from the perspective of the fourth image. North is to the left. The resolution of the images is 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’s the side of Europa visible here. Europa’s surface is crisscrossed with fractures, ridges, and bands, which have erased terrain more than 90 million years old. Citizen scientist Kevin M. Gill processed the images to improve color and contrast. Credit: NASA/JPL-Caltech/SwRI/MSSS, Kevin M. Gill CC BY 3.0

To assess the survival of amino acids on these worlds, the team mixed samples of amino acids with ice chilled to about -321 degrees Celsius. F (-196 Celsius) in sealed, airless vials, and bombarded them with gamma rays, a type of high-energy light, at different doses. Because oceans can host microscopic life, they also tested the survival of amino acids in dead bacteria in the ice. Finally, they tested samples of amino acids in ice mixed with silicate dust to see if material from meteorites or the interior could mix with surface ice.

Implications for future space missions

The experiments provided key data for determining the rates of amino acid decay, called radioactive decay constants. Using these constants, the team used the age of the ice surface and the radiation environment on Europa and Enceladus to calculate the depth of the craters and the locations where 10% of amino acids might survive radioactive destruction.

Although previous experiments have been conducted to test the survival of amino acids in ice, this is the first to use lower radiation doses that do not completely break down the amino acids, because simply changing or degrading them is enough to make it impossible to determine whether they are potential signs of life. This is also the first experiment to use 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 decomposed faster when mixed with dust, but decomposed more slowly when they came from microorganisms.

This image shows experimental samples loaded into a specially designed Dewar vessel, which will shortly be filled with liquid nitrogen and placed under gamma irradiation. Note that the fire-sealed test tubes are wrapped in cotton cloth to keep them together because the test tubes become buoyant in the liquid nitrogen and begin to float in the Dewar vessel, interfering with proper radiation exposure. Copyright: Candace Davison

“slow rates of amino acids” sour “The destruction of biological samples under surface conditions similar to those on Europa and Enceladus enhances the importance of future life-detection measurements by landing missions to Europa and Enceladus,” Pavlov said. “Our results suggest that the degradation rates of potential organic biomolecules in silica-rich regions on both Europa and Enceladus are higher than those in pure ice, and therefore potential future missions to Europa and Enceladus should be cautious in sampling silica-rich sites on both icy moons.”

A possible explanation for why amino acids persist longer in bacteria involves the following methods: Ionizing radiation Molecules are changed – directly by breaking chemical bonds or indirectly by creating nearby reactive compounds that in turn change or disassemble the desired molecule. It is likely that the bacterial cell material has protected the amino acids from the reactive compounds produced by radiation.

Reference: “Variable and significant losses of diagnostic biomarkers following exposure to simulated cosmic radiation in clay-rich and carbonate-rich soils Mars “Analog Samples” by Anaïs Roussel, Amy C. McAdam, Alex A. Pavlov, Kristin A. Knudson, Sherry N. Achilles, Denis I. Fostokos, Jason B. Durkin, S. Andrejkovicova, Dina M. Bauer, and Sarah Stewart Johnson, July 18, 2024, Astrobiology.
DOI: 10.1089/ast.2023.0123

The research was supported by NASA under award number 80GSFC21M0002, the NASA Planetary Science Division’s Internal Scientist Funding Program through the Goddard Core Laboratory Research Work Package, and NASA Astrobiology. n fold 80NSSC18K1140 Award.