Saturn’s ice moon may not be so cold beneath the surface.
In fact, a primordial world could be rumbling in the depths of its massive ocean.
Last year, scientists discovered Enceladus’s gravitational asymmetry—the pull of gravity is weaker near the south pole—but they were confused as to why the gravity at this location was weaker than it should be in icy terrain, given that the depression in the landscape there is so large. They discerned that water, which is 8% denser than ice, must be making up the difference. Based on that information, they calculated that a sea up to six miles thick probably exists 20 to 25 miles beneath the surface.
What’s more, they had proof that this water was coming into direct contact with Enceladus’ rocky core. NASA’s Cassini spacecraft found tiny dust nanoparticles rich in silicon escaping from Saturn’s ring system. Scientists studied their spectra, and found that they were made of silicon dioxide, or silica, which is a trademark of water-rock interactions found on Earth. They postulated that hydrothermal vents may be generating some of these particles, making for chemical conditions conducive to life.
The particles originated in Saturn’s E-ring, which is also home to ice particles known to come from Enceladus. Here’s Amina Khan, writing for the Los Angeles Times:
The scientists then ran experiments in the lab to determine how such silica particles came to be. With the particles’ particular makeup and size distribution, they could only have formed under very specific circumstances, the study authors found, determining that the silica particles must have formed in water that had less than 4% salinity and that was slightly alkaline (with a pH of about 8.5 to 10.5) and at temperatures of at least 90 degrees Celsius (roughly 190 degrees Fahrenheit).
The heat was likely being generated in part by tidal forces as Saturn’s gravity kneads its icy moon. (The tidal forces are also probably what open the cracks in its surface that vent the water vapor into space.)
Somewhere inside the icy body, there was hydrothermal activity—salty warm water interacting with rocks. It’s the kind of environment that, on Earth, is very friendly to life.
The researchers say that since these silica particles haven’t yet clumped together, they must be recent refugees of Enceladus. In other words, this hydrothermal activity is likely still happening now—knowledge that greatly expands astrobiologists’ outlook in the search for life beyond Earth. Still, they’ll have to find out how long this activity has been going on, and how stable it is, in order to consider Enceladus the top contender.