"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."

Europa and Enceladus, moons of Jupiter and Saturn respectively, have icy surfaces bombarded by high-speed particles trapped in their planets' magnetic fields and cosmic radiation from deep space events. Despite these hostile conditions, both moons have subsurface oceans heated by tidal forces from their host planets and neighboring moons, which may harbor life if they contain essential elements, compounds, and an energy source.

The research team conducted radiolysis experiments using amino acids to simulate biomolecules on these moons. Amino acids, which can be produced by life or non-biological chemistry, are vital to life on Earth as they are building blocks for proteins. Proteins play crucial roles in forming enzymes and structures necessary for life. The team suggested that geyser activity or the slow movement of ice could bring these amino acids from the subsurface oceans to the surface.

To assess the amino acids' survival, the researchers mixed them with ice chilled to approximately minus 321 Fahrenheit (-196 Celsius) in sealed, airless vials, then exposed them to various doses of gamma-rays. They also tested amino acids in dead bacteria and in ice mixed with silicate dust to simulate possible contamination from meteorites or internal material mixing with surface ice.

The experiments produced critical data on amino acid degradation rates, known as radiolysis constants. Using these constants, the team calculated the depths and locations on Europa and Enceladus where amino acids could survive radiolytic destruction.

This study marks the first to evaluate amino acid survival in conditions mimicking those of Europa and Enceladus, including in microorganisms and mixed with dust. The findings indicate that amino acids degrade faster when mixed with dust but slower when derived 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."

The study suggests that amino acids in bacteria may be shielded from reactive compounds produced by radiation due to the protective effects of bacterial cellular material.

Related Links
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