Scientists at NASA have uncovered evidence suggesting that Pluto's moon Charon once featured a subterranean ocean — one that eventually burst through to the surface as it froze and turned to ice. What an amazing sight that must've been. Images beamed back by the New Horizons spacecraft show a fractured landscape on Charon. A new theory put forth by NASA scientists proposes that a significant portion of these features, including numerous ridges, scarps and valleys, were caused by a subterranean ocean that eventually froze and expanded, forcing itself to the surface.
Here's how it probably played out: Millions of years ago when Charon was still in its early stages, its surface was kept warm by heat produced by the decay of radioactive elements and the residual heat left over from its formation. Any water ice on the surface would have melted and seeped down to create a subsurface ocean. But as the moon cooled over time, this ocean eventually turned to ice — and we all know what happens when water turns to ice: it expands. This process would have lifted the outermost layers of the moon to create the massive chasms now evident on the surface. NASA said this would have caused the moon's surface to "stretch and fracture on a massive scale".
A region on Charon called Serenity Chasma illustrates this process. This area, located along the moon's equatorial belt, is one of the longest chasms seen anywhere in the Solar System. It's about 1,800km long and at times 7.5km deep. To put its size in perspective, the Grand Canyon is "just" 446km long, and a smidge over 1.6km deep.
Multiple views of Serenity Chasma allowed NASA to create topographical maps of this expanse, and its features are consistent with this proposed geological process; measurements suggest that Charon's water ice layer was at least partially liquid in its early history, and has since refrozen. This process is reflected today in Charon's beautiful, but tortured, landscape.
Image credit: NASA/New Horizons