The hypothesis of an underground ocean on the dwarf planet Pluto was revived by some research based on data collected by NASA’s New Horizons space probe during its July 14, 2015 flyby. Generally the hypothesis concerns an ocean of water but William McKinnon, professor of earth and planetary sciences in Arts & Sciences at Washington University in St. Louis and one of the authors of some studies on Pluto, suggested that the ocean contains a lot of ammonia.