Signs of life on ocean moons may be just below the surface

• Signs of life might survive beneath the ice surface of some ocean moons, including Saturn’s moon Enceladus and Jupiter’s moon Europa.
• Future space missions might need to dig only inches below their surfaces to find these organics.
• So prospects for life-detection via future space missions to these ocean moons is now enhanced.

Signs of life on ocean moons hiding just beneath the surface?

Last December, NASA said amino acids could survive intact in the water vapor plumes of Saturn’s moon Enceladus. Now, a new study from researchers at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, suggests amino acids and other organic molecules could also survive just beneath the surface ice of moons like Enceladus and Europa. On July 18, 2024, the researchers said future landers may only need to dig a few inches deep into the ice to find such organics.

The research team published their intriguing peer-reviewed results in the journal Astrobiology on July 18, 2024.

Icy moons Enceladus and Europa

Enceladus and Europa are both ocean moons. They have global water oceans beneath their outer ice crusts. Those alien seas may be suitable for some forms of life. The surfaces, though, are much harsher with almost no atmospheres to speak of and intense radiation from the sun blasting them.

Some scientists say future robotic lander missions would likely need to drill deep down through the ice crusts to find any possible organic traces of life. Maybe even down into the oceans themselves. Missions like that are a long way off, though.

But now, it seems that may not be necessary after all. The new study reports a lander would only need to dig or drill down a matter of inches on Europa, and even less on Enceladus.

Lead author Alexander Pavlov at NASA’s Goddard Space Flight Center explained:

Based on our experiments, the “safe” sampling depth for amino acids on Europa is almost 8 inches (around 20 cm) 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. 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 mm) from the surface.

Experimenting with amino acids

Amino acids are a key component of life on Earth. They are the building blocks of proteins. They can be created either by life or other kinds of chemistry not related to life. If scientists discovered amino acids on the ocean moons, especially those that life on Earth uses to help build proteins, it would be exciting.

On moons like Enceladus and Europa, amino acids could come up to the surface in a couple of different ways. One is by geysers, already known to exist on Enceladus and tentatively on Europa. The water would bring them up from the ocean below and eject them into space through cracks in the icy surface. Another way is by the slow churning of the ice crust itself, bringing them and other materials to the surface.

With that in mind, the researchers used amino acids in radiolysis experiments to represent possible biomolecules. Radiolysis is the dissociation of molecules by ionizing radiation. The researchers wanted to simulate conditions on the surfaces of the moons and see if the amino could tolerate them without being destroyed.

Ice, dead bacteria and dust

The team combined various amino acids with ice chilled to about -321 Fahrenheit (-196 C) in sealed, airless vials. Then they bathed the vials in gamma rays at various doses. This simulated the deadly radiation coming from the sun, which hits the surfaces of the moons at full blast.

In addition, the team used amino acids in dead bacteria. The reasoning was there might be microbes living in the oceans right now, and when an organism dies, its remains could make it up to the surface where the amino acids it contained could be identified by a lander.

Lastly, the researchers also tested amino acids in ice mixed with silicate dust. This was the first-ever test of amino acids mixed with dust. Such dust could come from either meteorites or from within the moons themselves.

Degradation of amino acids

The radiolysis experiments allowed the researchers to estimate both the best locations and drilling depths in the ice to find 10% of the amino acids. They also determined the rates at which the amino acids would break down, called radiolysis constants.

This was the first testing of amino acids in ice to use both lower and higher radiation doses, and also to replicate surface conditions on the ocean moons. With lower radiation, the amino acids can be altered but are not destroyed. That can, however, still make it difficult to determine whether the amino acids came from life or abiotic (non-life related) chemical processes.

Interestingly, the results showed amino acids coming from microorganisms survived better than those mixed with dust. That’s good news for future missions going back to Enceladus and Europa. As Pavlov explained:

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. Our results indicate 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.

Earlier this year, another study suggested amino acids could even survive in Venus’ atmosphere, despite the high concentrations of sulfuric acid.

Bottom line: NASA scientists said we could find evidence of life on ocean moons like Europa and Enceladus by looking for amino acids just inches below their icy surfaces.

Source: Radiolytic Effects on Biological and Abiotic Amino Acids in Shallow Subsurface Ices on Europa and Enceladus

Via NASA

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