Something's wetting the surface of dwarf planet Pluto along the northern edge of Sputnik Planitia, and planetary scientists have found a good explanation for it. A recent study of new Horizons images taken during the 2015 flyby revealed evidence that liquid nitrogen is rising up through cracks in Sputnik Planitia. That's the giant heart-shaped glacial basin we see in all the Pluto images taken by the spacecraft.