NASA’s historic flyby of Pluto by the New Horizons spacecraft has yielded a wealth of new discoveries — but the latest one about its moon Charon is truly amazing.

Data from New Horizons indicates that Charon may have once had a large subsurface ocean, which could have causes cracks on the surface of the moon seen in some recent pictures, according to a Washington Post report.

The tectonic landscape of the moon indicates there has been some expansion and swelling, resulting in the cracks. The pocked surface of Charon is covered in water ice, and it may have once been relatively warm — warm enough for a large amount to have pooled deep below the surface. After a while, the heat would have dissipated and the subsurface ocean would have been frozen, expanding and causing the moon to crack from underneath.

As NASA described in a statement: “The side of Pluto’s largest moon viewed by NASA’s passing New Horizons spacecraft in July 2015 is characterized by a system of “pull apart” tectonic faults, which are expressed as ridges, scarps and valleys—the latter sometimes reaching more than 4 miles (6.5 kilometers) deep. Charon’s tectonic landscape shows that, somehow, the moon expanded in its past, and – like Bruce Banner tearing his shirt as he becomes the Incredible Hulk – Charon’s surface fractured as it stretched.”

Charon is a fascinating piece of space rock, as it is half the size of Pluto, the body it orbits, and it is closer to its host than any other satellite observed in our solar system. It’s almost another dwarf planet itself — more like two binary planets orbiting each other than a typical planet and moon relationship. Charon is also interesting because of its apparently complex geology, as opposed to surface covered in craters like our own moon — it has very long canyon systems that are fourtimes as long and deep as the Grand Canyon, according to the report.

A subsurface ocean would put it in the company of other moons in our solar system, like Europa, Enceladus, and Ganymede.