New research suggests there are locations on the surface of Saturn’s moon, Enceladus, where spacecraft can land to pick up clean traces of essential ingredients for life. These biosignatures are believed to originate from the ocean floor within the world’s icy shell.
Enceladus it has long been known that there are organic molecules – compounds composed of carbon, oxygen and nitrogen – under its seabed. Before it fell over the Saturn in 2017, the Cassini spacecraft flew through plumes of material that exploded through fissures on the surface of Enceladus, detecting organic molecules such as methane and ethane as well as other complex compounds reaching great altitudes.
About 90% of the larger grains of this material, launched thousands of miles above Enceladus, never escape the Saturnian system. Instead, they will fall back to the surface of the Saturnian moon, scientists now say, where they could theoretically be collected and examined by spacecraft.
“We can learn a lot about the potential biosignatures of Enceladus’ ocean by sending a mission to the surface of Enceladus. plume grains and gases,” Amanda R. Hendrix, senior scientist at The Planetary Science Institute and research leader, said in a statement. “But now we know that you can land on the surface and be confident that your instruments can measure relatively pure organic plumes – from the ocean.”
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Some organic molecules in Enceladus’ plumes that could be fingerprints of biological life, however, can be destroyed by ultraviolet (UV) from the sun. That means there is a desire to reach these molecules while they remain intact.
“We know that Enceladus’ ocean is habitable thanks to the Cassini measurements. We know that there is liquid water, energy, and the chemicals carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. It the ingredients necessary for life as we know it,” Hendrix said. “If we want to know if any ocean-derived biosignatures are present in the plume grains, we need these grains to be as pure and UV-resistant as possible.”
Hunt for clean material on Enceladus
To find an area on Enceladus where such pure material could be used, Hendrix and the team analyzed data from Hubble Space Telescope and Cassini spacecraft to see how deep photons of UV light can penetrate the surface of the moon.
“What we found in this study is that there are places on the surface of Enceladus where we can land with a spacecraft and take a sample — and we’re measuring relatively pristine organics,” Hendrix said. “That’s because solar ultraviolet (UV) photons don’t really penetrate the frozen surface very well.”
The team discovered that harmful UV photons can only penetrate about 100 micrometers into the icy surface of Enceladus, which is the width of a few human hairs.
“So that the highest part of the surface is exposed to harmful UV photons, but only a percentage of the organics are chemically transformed, and soon that material is covered by fresher plume material,” explained Hendrix. “And the deeper grains don’t undergo further modification – because the UV photons are prevented from interacting with the deeper material.
The results gathered by the team are useful because they tell the scientists that the Enceladus missions have a lot of organics to sample without having to analyze too much.
“Because UV light quickly changes organic molecules, the depth that such light travels to the surface of an ice-covered world is very important. With the short UV penetration depth found , our results confirm that there is enough organic material locked and preserved in the ices of Enceladus to be traced back to its ocean,” Christopher House, co-author of the research and a scientist at Penn State University, said in the statement. “It’s amazing to think that with known technology, we could easily access a lot of organic material from a habitable extraterrestrial ocean.”
The team’s research was published December 18 in the journal Earth and Environment Communication.
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