I’ve written surprisingly little here about Europa. Surprising, because it’s easily one of the most interesting objects in our solar system. Perhaps I have a habit of favouring the underdogs, but if there’s any other place in the solar system where we might find life, Europa is a pretty good bet. Actually, it’s an exceptionally good bet. The idea that under Europa’s smooth icy surface may lie a vast ocean full of water, warmed by Jupiter’s relentless gravitational squeezing is… compelling.
Tidal heating by jupiter is the reason why all four of the Gallilean Moons (Io, Europa, Ganymede, and Callisto) are rather interesting. Jupiter’s gravity is responsible for Io being the most volcanic object known, and both Callisto and Ganymede have been suggested to harbour subsurface oceans. But none of them is quite as dramatic as Europa. Europa’s surface is made of ice. It’s expected that there may be more liquid water under that thick icy crust than in all of Earth’s oceans put together. Europa’s secret ocean, hidden deep inside a solid shell. An interesting thing about Europa’s surface is that it’s also the smoothest object in the solar system. Smooth, but not perfectly smooth.
Parts of Europa’s surface are actually not very smooth at all. There are patches which have been dubbed “chaos terrain” where Europa’s surface is particularly rough, and recently, an intriguing explanation has been put forward — perhaps Europa may have subsurface lakes as well as an ocean!
The chaos terrain consists of dark patches of brownish ice, in which hulking icebergs seem to be embedded. It was long thought that the chaos terrain had something to do with liquid water, but no one was quite sure what. No one, until a team led by Britney Schmidt from the University of Texas. The key lay in the fact that the chaos terrain was inconsistent. Some patches raised, some sunken. This helped them build up a picture of what might be happening under all of the ice. Warm water welling up from deeper in the moon would pool into a subsurface lake, weakening the surface ice above and causing it to slump downwards. A mixture of partially molten ice and still frozen icebergs – a little like a slushie, but rather a lot bigger. The ice would then gradually re-freeze, expanding, and bloating outwards.
So could these lakes, lying above Europa’s deeper ocean, provide a harbour for life? That much, we can’t tell. Not yet, anyway. But the thought that there may be water only a few kilometres below Europa’s surface, makes the prospect of drilling down to look a lot more feasible than trying to reach the ocean hundreds of kilometres deeper.
The paper was published a couple of months ago in Nature, if you care to read it for yourself…
As an aside, it finally struck me that any lifeforms on Europa would be correctly termed “Europeans”. Though if you ask me, it seems like a long way to go for espresso and croissants…