Since New Horizon’s 2015 flyby of Pluto, scientists have been studying the craft’s high-resolution photographs of the dwarf planet. A group of researchers led by Dale P. Cruikshank of NASA Ames Research Center and Cristina M. Dalle Ore, a member of the center as well as the SETI Institute, noticed one trench that was brighter in color than the surface around it. Closer examination showed that nearby craters and troughs had a smoother appearance than the surrounding area. IR spectra from the same spacecraft indicated these regions had higher concentrations of water ice and ammonia than the surrounding area. The researchers say that, all together, the evidence suggests that a cryovolcano, or ice volcano, had erupted inside the trench (Sci. Adv. 2019, DOI: 10.1126/sciadv.aav5731). The presence of ammonia in the trench led the researchers to conclude that eruption happened within the last billion years; otherwise, ultraviolet radiation and ionic bombardment would have destroyed the compound. Dalle Ore says the discovery supports previous suggestions that Pluto has active volcanism and an internal ocean, from which this eruption would have originated.