Geography of Pluto

This is the convention used by the International Astronomical Union (IAU) and the New Horizons team, and their maps put the sunlit hemisphere on top.

These names were variously taken from historical figures involved in the study of Pluto, notable space exploration missions, and a variety of chthonic deities or demons, some from ancient mythology and others from modern popular culture.

The lack of craters in the region suggests that its surface is less than 100 million years old, hence the speculation that Pluto is probably geologically active.

Potentially recent glacial activity, near Cthulhu Macula, is suggested by the presence of lighter-hued material overlaid on top of darker, more ancient portions; according to Lillian Gipson at NASA, "...In the southernmost region of the heart, adjacent to the dark equatorial region, it appears that ancient, heavily-cratered terrain (informally named “Cthulhu Regio”) has been invaded by much newer icy deposits.

[16] The dark color of the area is speculated to be the result of a "tar" made of complex hydrocarbons called tholins covering the surface, formed from methane and nitrogen in the atmosphere interacting with ultraviolet light and cosmic rays.

[23] The Working Group for Planetary System Nomenclature of the International Astronomical Union (IAU) is responsible for assigning official names to surface features on Pluto.

The New Horizons science team invited members of the public to propose names and vote on them before the spacecraft's arrival.

The portions of Pluto's surface mapped by New Horizons (in enhanced color). Center is 180 degrees longitude (diametrically opposite the moon Charon). The bright area in the center is Tombaugh Regio. The dark area to the west is Cthulhu Macula. The series of dark areas to the east are the "Brass Knuckles".
Tombaugh Regio, as viewed by New Horizons 13 July 2015
The "Brass Knuckles" region of Pluto. Meng-p'o is at the zero meridian; to the east is the 'tail' of Belton Regio. Note that the Safronov Regio is labeled as "Krun" in this image.
Dune fields in Sputnik Planitia near the foothills of Al-Idrisi Montes
Informally named geographic features