Wednesday, September 16, 2015

NASA confirms there's a global subsurface ocean on Enceladus

We've known there is water on Enceladus for a while now, but NASA has just confirmed a more recent theory about the icy moon of Saturn: it has a subsurface ocean that spans the entire globe. The news comes just a handful of months after the agency discovered evidence of hydrothermal vents, which are believed to be integral to the formation of life here on Earth.
The confirmation was made using research from Cassini — a spacecraft that arrived at Saturn in 2004 and has spent the last decade studying the planet and its many moons. (It was launched in 1997.) The researchers used Cassini to measure the wobble in Enceladus' orbit of Saturn, something that "can only be accounted for if its outer ice shell is not frozen solid to its interior."
Enceladus is one of a handful of worlds in our Solar System where you can see liquid jets erupting from its surface, and it didn't take longafter Cassini arrived before NASA was able toconfirm that the moon was leaking liquid water. But while previous studies of Enceladus had hinted at a subsurface sea, it was thought that the body of water was lens-shaped, and perhaps only occupied a portion of Enceladus' underbelly.

"This was a hard problem that required years of observations, and calculations involving a diverse collection of disciplines, but we are confident we finally got it right," Peter Thomas, a Cassini imaging team member at Cornell University, and lead author of the paper, said in a release detailing the news.
The team painstakingly measured and tracked the movement of Enceladus, and eventually discovered that Saturn's gravity was rocking the moon in its orbit ever so slightly. They were able to use this information to model the interior of the moon. If the surface and core of Enceladus were rigidly connected, there would be too much dead weight and that wobble would be less pronounced. The only thing that could account for such an exaggerated wobble was the existence of a global layer of liquid that separates the surface from the core.
Cassini is far from done with Enceladus. The spacecraft will make an extremely close flyby at the end of October — just 30 miles (49 kilometers) above the surface — and it will buzz through one of the plumes of icy material.
Enceladus is not alone when it comes to subsurface oceans. Europa — one of Jupiter's moons — also contains a subsurface ocean, and is the target of one of NASA's next flagship science missions. And this past March, NASA confirmed that Ganymede, another moon of Jupiter's, also has a subsurface ocean. Evidence of water and water ice exists on many other moons and planets, too. It seems as if no matter where we look, we see water — even if it takes a while to find it.



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