Mordor Macula /ˈmɔːrdɔːr ˈmækjʊlə/ is the informal name for a large red area about 475 km in diameter near the north pole of Charon, Pluto's largest moon.^[1][2] It is named after the black land called Mordor in J.R.R. Tolkien's The Lord of the Rings.

The origin of Mordor Macula is not completely understood. It may be a deposit of frozen gases captured from Pluto's escaping atmosphere.^[3][4] A leading hypothesis 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 hypothesis implies that a similar red spot should exist on Charon's south pole as well—and indirect evidence suggests this is true.^[5]

It is also possible that the Mordor Macula has a cryovolcanic origin.^[6]

• List of geological features on Charon