The origin of Mordor Macula is not completely understood. It may be a deposit of frozen gases captured from Pluto's escaping atmosphere, a large impact basin, or both. A leading theory is that nitrogen and methane escape from Pluto and are then deposited into the cold poles of Charon, where scattered ultraviolet light then transforms the molecules into tholins. This theory implies that a similar red spot should exist on Charon's south pole as well—and indirect evidence suggests this is true.