It appears to be a frozen former lake of liquid nitrogen
Millions or billions of years ago, liquids might have pooled on the surface of Pluto, a new photograph captured by NASA’s New Horizons spacecraft shows.
The image, captured by the spacecraft on July 14 and published by NASA on Thursday, appears to show a frozen former lake of liquid nitrogen situated in a mountain range, NASA said in a post about the photo. The lake is as much as 20 miles wide at one point.
“In addition to this possible former lake, we also see evidence of channels that may also have carried liquids in Pluto’s past,” said Alan Stern, principal investigator of New Horizons, in a post published by NASA.