Many scientists have long suspected that Saturn's moons, some of which feature subsurface oceans, may be a good bet for discovering life beyond our planet, and this week a pair of new studies make an even better case for that on the moon Enceladus. According to new findings, Enceladus may be exhibiting hydrothermal activity in its subsurface ocean that's similar to what we see in Earth's oceans, and if that's true, the ocean's temperatures may be able to support life.
If you're not familiar with hydrothermal activity, it's basically what happens when seawater interacts with openings in the rocky crust beneath the ocean floor. The heat and minerals beneath the ocean floor interact with the water, which then spews out of the openings as a mineral-laden, heated solution. It's a natural occurence in our oceans, and you've seen it in action if you've ever seen documentary footage of "vents" on the ocean floor. Now, thanks to two new papers, NASA believes the same thing happens on Enceladus.
“These findings add to the possibility that Enceladus, which contains a subsurface ocean and displays remarkable geologic activity, could contain environments suitable for living organisms,” said John Grunsfeld, astronaut and associate administrator of NASA's Science Mission Directorate in Washington. “The locations in our solar system where extreme environments occur in which life might exist may bring us closer to answering the question: are we alone in the Universe.”
We know about the hydrothermal activity on Enceladus thanks to geysers that erupt from the moon's surface, spewing out ice and vapor from the ocean below. According to a new study published this week in Nature, the Cassini spacecraft currently exploring Saturn and its moons began detecting microscopic grains of silica around Saturn years ago via its cosmic dust analyzer (CDA). Because of the consistent size of these grains, scientists were able to trace them to a specific geologic process, and conducted an extensive four-year study complete with laboratory experiments and computer models to determine the exact way in which these grains found themselves floating out in space around Saturn. Their conclusion: The grains originated in the rocky crust beneath Enceladus' ocean, then traveled up in a heated water solution that was at least 194 degrees Farenheit, where they eventually made contact with cooler water and, finally, left the moon via geyser.
"It's very exciting that we can use these tiny grains of rock, spewed into space by geysers, to tell us about conditions on -- and beneath -- the ocean floor of an icy moon," said the paper’s lead author Sean Hsu, a postdoctoral researcher at the University of Colorado at Boulder.
A second paper, published recently in Geophysical Research Letters, concerns the study of large amounts of methane found in a plume of gas erupting from around Enceladus' south pole. Because the methane, also detected by the Cassini spacecraft, is so abundant in this plume, French and American scientists did "extensive modeling" to determine just why and how there's so much of it, particularly when their data suggests that high pressure in Enceladus' ocean would imprison methane in crystalline ice structures called "clathrates," depleting the amount of methane in the ocean.
The researchers explored two different scenarios: one, that hydrothermal processes within Enceladus -- the same processes that produced the silica grains -- produce so much methane that it's ejected out in the plume before it can be converted into clathrates; or two, that the clathrates full of methane are simply pulled along by the plume and release their methane on the way up. According to NASA, the authors of the paper "agree both scenarios are likely occurring to some degree, but they note that the presence of nanosilica grains, as documented by the other paper, favors the hydrothermal scenario."
So we've got two different studies pointing to heated water laden with minerals rising up from the bottom of an ocean on one of Saturn's moons in a manner very similar to Earth's oceans. We don't know yet if all this hydrothermal activity could bring with it the possibility of life in the waters of Enceladus, but it's an exciting new prospect in the exploration of our solar system.