NASA researchers have found that amino acids, potential indicators of life, could survive near the surface of Jupiter's moon Europa and Saturn's moon Enceladus.
Experiments indicate that these organic molecules can withstand radiation just under the ice, making them accessible to future robotic landers without deep drilling.
Potential for Life on Icy Moons
Europa and Enceladus have long intrigued scientists due to the presence of subsurface oceans beneath their ice crusts. These oceans, heated by tidal forces from their host planets and neighboring moons, could harbor life if they contain the necessary elements and compounds. A NASA experiment suggests that if these oceans support life, signatures of that life, such as amino acids, could survive just under the surface ice despite the harsh radiation.
Alexander Pavlov of NASA’s Goddard Space Flight Center, lead author of the study published in the journal Astrobiology, explained, “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 in the area where the surface hasn’t been disturbed much by meteorite impacts.” He further added, “Subsurface sampling is not required for the detection of amino acids on Enceladus—these molecules will survive radiolysis at any location on the Enceladus surface less than a tenth of an inch from the surface.”
NASA's Experimental Approaches and Findings
The research team conducted radiolysis experiments using amino acids as representatives of biomolecules. Amino acids can be created by both biological and non-biological processes. Finding certain types of amino acids on Europa or Enceladus would be a potential sign of life because they are used by terrestrial organisms to build proteins. These proteins are essential for life as they create enzymes that regulate chemical reactions and form structures.
To evaluate the survival of amino acids on these moons, the team mixed samples of amino acids with ice chilled to about minus 321 degrees Fahrenheit (-196 degrees Celsius) in sealed, airless vials and bombarded them with gamma rays. They also tested the survival of amino acids in dead bacteria in ice and in ice mixed with silicate dust, simulating the potential mixing of material from meteorites or the moon’s interior with surface ice.
The experiments provided pivotal data on the rates at which amino acids break down, known as radiolysis constants. Using these rates, the team calculated the drilling depth and locations where 10% of the amino acids would survive radiolytic destruction. Pavlov emphasized the significance of these findings, stating, “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.”
Implications for Future Missions
The results indicate that future missions to Europa and Enceladus could detect amino acids without the need for deep drilling, significantly simplifying the search for life. Pavlov noted, “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.”
These findings highlight the importance of considering the radiation environment and the composition of surface ice when planning future missions. The research underscores the potential for life-detection missions to make significant discoveries with relatively shallow subsurface sampling.
The team found that amino acids degraded faster when mixed with dust but slower when derived from microorganisms. This suggests that bacterial cellular material may protect amino acids from reactive compounds produced by radiation. Pavlov explained the significance of this protective effect: “It’s possible that bacterial cellular material protected amino acids from the reactive compounds produced by the radiation.”
This protective mechanism could be crucial in preserving biomarkers in the harsh environments of Europa and Enceladus, increasing the likelihood of detecting signs of life if they exist.
The study provides a strong foundation for future research and mission planning aimed at detecting life on icy moons. By refining the understanding of how amino acids and other organic molecules survive in these environments, scientists can better design instruments and sampling strategies for upcoming missions. The ongoing exploration of Europa and Enceladus holds great promise for uncovering the secrets of these fascinating worlds and advancing the search for extraterrestrial life.