Astronomers from the U.K. and Germany analyzed data from the Hubble Space Telescope to uncover the planet's chemical makeup. They found evidence of larger amounts of oxygen than could be explained by GD 61's atmosphere. That extra oxygen must be bound to either water or carbon, Boris Gänsicke, a University of Warwick astronomer who studied the planet, said in a statement. (Oxygen binds to carbon as carbon dioxide.) In this case, Farihi, Gänsicke and their third collaborator, Detlev Koester of the University of Kiel, found very little carbon in GD 61, so they concluded the oxygen must be evidence of water.