Charon’s surface cracked when ancient subsurface sea froze

Pluto’s largest moon Charon is busting at the seams, and an ancient subsurface ocean might be to blame.

Ridges and valleys more than 6 kilometers deep, seen during the July 14 flyby of the New Horizons spacecraft (SN: 12/26/15, p. 16), suggest that the moon swelled at some point in its past. The rifts could have been carved by an ocean that froze and expanded, tearing apart the satellite’s surface, NASA announced February 18.

Today, Charon is laden with water ice. But long ago, heat left over from the moon’s formation and from the decay of radioactive elements could have melted some of the ice and sustained an underground ocean. As the moon cooled and the water froze, the newly formed ice would have expanded, creating the cracked surface seen today.

One of these fractures is part of Serenity Chasma, the informal name for the one of the longest series of chasms in the solar system. With a length of 1,800 kilometers, Serenity is about four times as long as the Grand Canyon.