When New Horizons first returned images of Pluto and Charon, one thing was immediately apparent – their surfaces were not the barren, featureless places we had been expecting. Instead, they are pockmarked by craters, mountains, and more.
But one feature in particular on Charon has caught the eye of astronomers. Informally named Serenity Chasma, this canyon has two steep walls and is part of a long system of chasms, one of the longest in the Solar System. The whole system is about 1,800 kilometers (1,100 miles) long and up to 7.5 kilometers (4.5 miles) deep, giving the moon a vast equatorial “belt”.
According to NASA, a subsurface ocean may have been the cause of this canyon. We know the outer layer of Charon is mostly ice, but the interior moon may have once been warm enough to melt this ice under the surface, forming a vast ocean not too dissimilar to that on Europa or Enceladus.
When Charon began to cool, this ocean froze and thus expanded as the water turned to ice. This would have stretched the surface, forming the so-called “pull apart” faults we can see today. Indeed, similar features are found on other worlds like Europa, although in that instance it’s thought to be caused by the tidal effect of Jupiter.
The topography of the region has been color-coded here. NASA/JHUAPL/SwRI
Nonetheless, an ancient ocean on Charon would be a significant finding, showing that liquid water really can spring up in all places in the Solar System. This could have implications for the chances of life starting elsewhere aside from Earth, although of course, no one is jumping to the conclusion that Charon may once have been habitable under its surface yet.
The image of the Serenity Chasma region was captured by the Long-Range Reconnaissance Imager (LORRI) on New Horizons during its closest approach on July 14, 2015. The image was taken from a distance of about 78,700 kilometers (48,900 miles), with a resolution of 394 meters (1,290 feet) per pixel.