CAPE CANAVERAL - Evidence is mounting for an ocean of slushy water at Pluto, buried beneath its frozen heart.

Scientists said Wednesday that Pluto may have rolled over on its axis eons ago, the result of tidal forces with jumbo moon Charon. They say an underground sea is the most likely explanation.

These latest findings are based on observations by NASA's New Horizons, which made an unprecedented flyby of Pluto last year. The spacecraft is now 365 million miles from Pluto and enroute to a 2019 close approach of another faraway orb.

Published in this week's journal Nature, the studies focus on a 600-mile basin in the left lobe of Pluto's heart-shaped region.

Close to the sun, meanwhile, Mercury has a big new valley. Scientists attribute surface buckling, caused by global contraction.