The Cassini probe finished its mission last September but its science output continues to surprise us when it comes to the Saturn system. The latest analysis reveals that complex organic molecules are present on Saturn's icy moon of Enceladus, another suggestive piece of evidence that life might have evolved there.
As reported in Nature, scientists have discovered large, carbon-rich molecules in the plumes ejected by the Saturnine moon. The probe had previously detected simple hydrocarbons and researchers also found evidence of hydrothermal activity in the liquid ocean beneath the icy surface.
“We are, yet again, blown away by Enceladus. Previously we’d only identified the simplest organic molecules containing a few carbon atoms, but even that was very intriguing,” co-author Dr Christopher Glein, from the Southwest Research Institute (SwRI), said in a statement. “Now we’ve found organic molecules with masses above 200 atomic mass units. That’s over 10 times heavier than methane. With complex organic molecules emanating from its liquid water ocean, this moon is the only body besides Earth known to simultaneously satisfy all of the basic requirements for life as we know it.”
Satisfying the requirement is great but it is not enough to claim a discovery. Biosignatures, the potential signals of life, are not as unequivocal as people might think. Complex chemistry could be a product of geological processes. What is clear from this new discovery is that if there is life on Enceladus, it has the means to prosper.
Our understanding of Enceladus comes from Cassini’s flyby through Saturn's plumes. The spacecraft used two of its instruments to analyze the content of the plumes, which included hydrocarbons and molecular hydrogen. Hydrogen was particularly intriguing for scientists as it is believed to have formed in chemical reactions between water and rocks around hydrothermal vents.
“Hydrogen provides a source of chemical energy supporting microbes that live in the Earth’s oceans near hydrothermal vents,” co-author Dr Hunter Waite, also at the SwRI, added. “Once you have identified a potential food source for microbes, the next question to ask is ‘what is the nature of the complex organics in the ocean?’ This paper represents the first step in that understanding – complexity in the organic chemistry beyond our expectations!”
Organic material on other bodies of the Solar System has been in the news a lot lately. Curiosity has discovered ancient organic molecules on Mars and researchers brought forth evidence suggesting that the dwarf planet Ceres is covered in them. But Enceladus might be the most exciting find yet.
Understanding if there is life on the faraway moon will require a new probe with more sensitive instruments. Such a mission is probably over a decade away and we need to be cautious about shouting “Life!” before we actually find it.