Sputnik Planitia in Color (IMAGE) University of Arizona Caption Sputnik Planitia (the left lobe of Pluto's "heart") is believed to be the outer solar system equivalent of a lunar "mascon" (mass concentration). Like mascons on the Moon, Sputnik Planitia is believed to be an impact basin, filled in with lavas (on Pluto, cryogenic ices take the place of lavas). Credit NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute Usage Restrictions This visual may only be used in conjunction of reporting/posting of this news release. Credit must be stated as indicated. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.