Ever since a massive subsurface ocean was discovered under the ice on Saturn’s moon Enceladus, scientists have sought to uncover the reason behind the existence of liquid water on a world that should be frozen solid. However, a new study not only illustrates what may be the mechanism behind the presence of Enceladus’ liquid water, but also that the process has been going on for billions of years — more than long enough for life to gain a foothold there.
Numerous theories on how Enceladus maintains a liquid ocean have been put forward since evidence for the presence of such an ocean was discovered by the Cassini space probe in 2005, but none of these theories matched what was being observed in the icy moon — by all rights, Enceladus should have frozen solid billions of years ago. This new study, a joint American-European endeavor, made use of complex computer models to discover a mechanism that seems to work.
Enceladus is a small, icy moon, 504 kilometers (313 miles) in diameter, in a 238,000-kilometer (147,900-mile) orbit around Saturn. Its surface is comprised of a 30 to 40 kilometer (19 to 25 mile) thick ice shell, that sits on top of a globe-spanning ocean 26 to 31 kilometers (16 to 19 miles) deep: for comparison, the Challenger Deep, the deepest point in Earth’s ocean, is a little shy of 11 kilometers, or 6.8 miles, deep. Underlying this massive ocean is the moon’s small rocky core, that may be porous enough to allow water to soak deep into its structure.
Cool water from Enceladus’ ocean sinks, as cold water is wont to, into the moon’s porous core, where it is eventually heated, casing it to rise back into the ocean, up toward the icy crust. This heating isn’t even, though, as the computer modeling indicated that the upwelling currents were stronger near the south pole, with the water getting as warm as 85ºC (185ºF) in some spots. This matches the location of the dramatic southern geysers recorded by Cassini, ejecting their plumes into space far enough for the vapor to form its own ring around Saturn, the E-Ring.
The computer modeling also indicates that this convection mechanism could have been functioning for billions of years, ample time for lifeforms of some sort to have evolved, especially considering life on Earth may have taken as little as 100 to 200 million years to form. Aside from a massive liquid ocean, Enceladus also hosts organic molecules that could form the foundation for biological life, and elemental hydrogen that could be used as a food source for microbial organisms.
- This three-image mosaic is the highest resolution view yet obtained of Enceladus' north polar region. NASA via Wikimedia Commons
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