New study suggests Pluto started out with a liquid ocean

The findings are based on an analysis of pictures of Pluto's surface taken by NASA's New Horizons mission. These show extensive ridges and troughs consistent with the planet expanding as its ocean froze. Pluto is thought to possess a liquid ocean beneath a thin icy surface and a mantle of watery ice, according to the paper, which was published on June 22. The study suggests the heat energy that allowed for a liquid ocean came from rocks colliding with and raining down on Pluto as the planet formed. Heat may also have been generated by radioactive elements in the rocks. The research suggests other big Kuiper Belt objects — the largest of which are Pluto, Eric, Haumea and Makemake — may also have once held liquid oceans on their surfaces.