The deep icy basin in Pluto's heart-shaped region may be a natural sinkhole.
In a study published on November 30, a team led by University of Maryland astronomer Douglas Hamilton suggests the basin may have resulted from the weight of surface ice.
Computer modeling by the researchers indicates an ice cap formed at that location early in Pluto's history. All that ice may have caused the underlying crust to slump, creating the 600-mile-wide basin in the left lobe of the heart, now called Sputnik Planitia. Other models point to a crater caused by an impact.
NASA's New Horizons spacecraft unveiled Pluto during last year's historic flyby.
Two weeks ago, another study in the journal Nature suggested an ocean beneath Sputnik Planitia. Hamilton says that still could be the case.