Cracks in Pluto's icy moon Charon may indicate that this far away planet once had an underground ocean.
Pluto has a surface temperature estimated to be about -380 degrees Fahrenheit (-229 Celsius) - temperatures far too cold to allow liquid water on its surface. And even though its moon harbors a similar frigid environment, new research suggests a subterranean ocean may have been possible.
Scientists believe that Charon - which presumably formed from a giant impact on Pluto, given its large size -had eccentric, or oval-shaped, orbits that could have generated large tides, causing friction and surface fractures.
"Depending on exactly how Charon's orbit evolved, there may have been enough heat from tidal deformation to maintain liquid water beneath the surface of Charon for some time," Alyssa Rhoden of NASA's Goddard Space Flight Center said in a press release.
Pluto's moon is not the only celestial body in the outer solar system whose cracks are revealing evidence of ocean interiors - Jupiter's moon Europa and Saturn's moon Enceladus are two examples.
These moons experience a sort of gravitational tug-of-war between their respective parent planets and neighboring moons, creating an oval orbit like Charon. These orbits raise daily tides that flex the interior and stress the surface. It is thought that tidal heating has extended the lifetimes of subsurface oceans on Europa and Enceladus by keeping their interiors warm.
Next month NASA's New Horizons spacecraft plans to be the first to visit Pluto and Charon, hopefully providing more detailed evidence that it too once had an underground ocean.
"Since it's so easy to get fractures, if we get to Charon and there are none, it puts a very strong constraint on how high the eccentricity could have been and how warm the interior ever could have been," Rhoden added. "This research gives us a head start on the New Horizons arrival - what should we look for and what can we learn from it."
Based on telescope observations of Pluto and Charon's current orbit, it is not expected to generate significant tides, so any ancient underground ocean may be frozen by now, according to Rhoden.