Enceladus’s Wet, Watery Secret

I owe one of Saturn’s moons an apology. Enceladus is on the shortlist of places in the Solar System that might support life, but I never took Enceladian life seriously. You see, Enceladus is really small. I mean really, really small. A mere 300 miles across.

For some time now, we’ve known Enceladus has liquid water beneath its surface. The cryovolcanos in the south polar region make it pretty obvious. You can see them erupting in the totally legit Hubble image above.

But how much water is there, and how long has it been liquid? Could an object so small and so far from the Sun really retain enough internal heat to support a vast, subsurface ocean similar to what we’ve found on Europa?

For the most part, the scientific literature has talked about a localized subsurface lake near the south pole or maybe just a tiny pocket of melt water. The kind of thing that might form periodically and then freeze solid again. This hardly sounds like a suitable environment for the evolution of life.

It was hard to believe in a vast subsurface ocean teeming with Enceladian microbes and Enceladian fish. Until now.

Just this month, an important new paper came out in the journal Icarus. It seems Enceladus rocks back and forth (“librates,” to use the technical term) a little too much to be solid all the way through. Something must be sloshing around inside, with the moon’s entire eggshell-like surface floating on top.

This discovery follows on the heels of another paper, published in July by Nature, which offered a global subsurface ocean as one of two possible explanations for an observed discrepancy in Enceladus’s cryovolcanic eruptions. The eruptions were occurring several hours after they should have according to previous models.

It’s interesting that not one by two scientific papers, each following different lines of research, came to almost the same conclusion. According to the paper in Nature, Enceladus might—just might—have a global subsurface ocean; and according to the Icarus paper, it totally does have an ocean, just like Europa.

None of this proves Enceladus has life, but that possibility seems a lot more credible in a global ocean than in tiny pockets of melt water.

So Enceladus, I’m sorry. I never should have doubted you.

P.S.: It’s still unclear how Enceladus maintains enough internal heat for its ocean. To quote the Icarus paper, “[…] a global ocean within Enceladus is problematic according to many thermal models […].” The best guess for now is that Saturn exerts more tidal forces on Enceladus than previously thought.

Links

Timing of Water Plume Eruptions on Enceladus Explained by Interior Viscosity Structure from Nature Geoscience.

Enceladus’s Measured Physical Libration Requires a Global Subsurface Ocean from Icarus.

What’s Inside Saturn Moon Enceladus? Geyser Timing Gives Hints from Space.com.

Enceladus: A Global Ocean from Centauri Dreams.