After crunching nearly a decade’s-worth of data, NASA scientists have resolved a long-standing mystery about Saturn’s wobbly, icy moon, Enceladus: It has a giant ocean hiding beneath its icy crust, and it wraps around the entire world.
This is big news for a few reasons. Way back in 2008, just four years after NASA’s Cassini spacecraft swung into orbit around Saturn, NASA said the spacecraft sampled a “surprising organic brew erupting in geyser-like fashion” from Enceladus.
This discovery hinted that Enceladus harbours all of the basic ingredients to support biological activity: warmth, water, and organic compounds.
“We have quite a recipe for life on our hands, but we have yet to find the final ingredient, liquid water,” Dennis Matson, a Cassini project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California said in a 2008 press release, “but Enceladus is only whetting our appetites for more.”
Now, seven years later, Cassini scientists have confirmed this icy moon’s ocean — which we’ve known about for a while — is not small and locked in one place, but is giant and flows around the entire span of the moon.
How to find an ocean
Enceladus is not a perfect sphere. It also goes faster at some parts of its orbit, and slower at other times. This causes Enceladus to rock back and forth a little as it circles Saturn.
Scientists knew of this small wobble in Enceladus’ orbit around Saturn, but couldn’t be certain that it meant a global ocean lurking below the moon’s surface. After analysing more than seven years’ worth of Cassini images and data, however, project scientists detected minute changes in the moon’s rotation — and described the wobble in detail.
The global ocean discovery came soon afterward.
After plugging the wobble data into a computer model, then simulating many different ways the moon’s insides might be structured, the team learned that a world mostly frozen to the core — as previously expected — couldn’t explain the wobble. Only a giant, liquid, and global subsurface ocean could.
“If the surface and core were rigidly connected, the core would provide so much dead weight the wobble would be far smaller than we observe it to be,” Matthew Tiscareno, a Cassini participating scientist at the SETI Institute, Mountain View, California, and a co-author of the paper said in a press release. “This proves that there must be a global layer of liquid separating the surface from the core.”
And where there’s water, there’s usually life.
“Everything we know about life says that it needs water,” journalist Corey Powell says in a Popular Science piece about the search for alien life in Jupiter’s moon, Europa. “Conversely, every place on Earth where water exists, life does too. The conventional thinking, then, is that if you want to find alien life, the first thing you look for is alien water.”
The story of Enceladus has evolved drastically since we first got hints of its icy plume in 2005. Since then we’ve found evidence of a regional sea in 2014, and have recently unearthed hints of hydrothermal activity on its ocean floor in 2015.
We still don’t know why Enceladus’ ocean isn’t frozen solid from its core to the surface, but mission scientists speculate that the heat generated from tidal forces originating from Saturn’s gravity may have something to do with it.
Either way, a bigger extraterrestrial ocean is good news to those answering NASA’s calls to search for alien life.
“[T]he ocean is habitable: it is composed of water of reasonable salinity and pH, contains organic material, and contains biologically useful energy sources,” Chris McKay, an astrobiologist at NASA’s Ames Research Center in California, told The Guardian earlier this year regarding an analysis of Enceladus’ water jets.
Cassini is scheduled to take its most detailed look at Enceladus’ icy jets with a close flyby on October 28, 2015.
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