There may be a liquid ocean beneath the icy surface of Titan, Saturn’s biggest moon.
Evidence of a sub-surface body of water comes from gravity measurements made by NASA’s Cassini spacecraft, which flew past Titan six times between 2006 and 2011.
As Titan orbits around Saturn, it’s stretched and squeezed by the planet’s gravitational pull. The resulting bulges or “tides” vary in size based on the composition of the moon. If Titan were made of solid rock and ice, the tides would be much smaller than what Cassini measured.
“The density of Titan is consistent with a body that is about 60% rock and 40% water,” Jonathan Lunine, one of the co-authors of the study, told Time’s Jeffrey Kluger. “The ocean must be fairly thick — a few hundred kilometers. And it must lie relatively close to the surface — beginning no farther down than 100 kilometers.”
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