<<The "Brass Knuckles" region of Pluto. Meng-p'o is at the zero meridian; to the east is the 'tail' of Cthulhu.
A series of semi-regularly spaced dark spots with irregular boundaries are nicknamed the Brass Knuckles. They average about 480 km in diameter and are located along the equator between the Heart and the tail of the Whale. The brass knuckles are separated from one another by tall uplands. There are also many canyons running through them and through the surrounding mountains that are hundreds of miles long and several miles deep. The Knuckles are:
Vucub-Came Macula and Hun-Came Macula, after the two leading death gods in the Popol Vuh text of the K'iche' Maya
Meng-p'o Macula, after a goddess from Chinese Buddhism who caused the dead to forget their past lives
Balrog Macula, after a fictional race of demons in J. R. R. Tolkien's fantasy mythos
Krun Macula, after a lord of the underworld in the Mandaean religion of southern Iraq
Ala Macula, after an underworld and harvest deity of the Igbo people of eastern Nigeria
A bright, ring-shaped feature about 350 km across located near the tail of the "Whale" in low-resolution images is nicknamed the "Donut". It does not appear as a ring in higher-resolution images. Cthulhu Macula is a prominent surface feature of the dwarf planet Pluto, that is reminiscent of a whale in shape. It is an elongated dark region along Pluto's equator, 2,990 km long and one of the darkest features on Pluto. It is west of the Sputnik Planitia region of Tombaugh Regio, also known as Pluto's "heart", and to the east of Meng-P'o, the easternmost of Pluto's "Brass Knuckles".
The dark color of the region is speculated to be the result of a "tar" made of complex hydrocarbons called tholins covering the surface, which form from methane and nitrogen in the atmosphere interacting with ultraviolet light and cosmic rays. Tholins have been observed on other planetary bodies, such as Iapetus, Umbriel, and in the atmosphere of Titan, although the irregular and disconnected nature of the dark spots on Pluto has not yet been explained. The presence of craters within Cthulhu indicates that it is perhaps billions of years old, in contrast to the adjacent bright, craterless Sputnik Planitia, which may be as little as 100 million years old; however, some areas of Cthulhu Macula are smoother and much more modestly cratered, and may be intermediate in age. The western 'head' region consists mostly of heavily cratered 'alpine' terrain. The middle part of Cthulhu Macula is meanwhile a smooth plain, probably formed through large cryovolcanic eruptions, like Vulcan Planum on Charon. This part appears to be younger than the alpine terrain to the east, but there are nevertheless several large craters located in this region. The western 'tail' region of Cthulhu Macula was imaged in much lower resolution than the eastern part, but it can be inferred that this is a hilly landscape bordered by mountains to the west. Higher-resolution images of the border between the two regions indicate that lighter material from Sputnik Planitia, composed of nitrogen, carbon monoxide, and methane ices, may be invading and overlaying the easternmost part of the dark Cthulhu Macula.
"Cthulhu" was named after the fictional deity from the works of H. P. Lovecraft and others. The character Cthulhu initially appeared in Lovecraft's 1928 short story "The Call of Cthulhu", as a malevolent entity hibernating within an underwater city in the South Pacific. In the book, it is the subject of worship by a number of human cults asserting that while it is currently trapped, Cthulhu will eventually return. In many of Lovecraft's stories, particularly The Whisperer in Darkness, the transneptunian planet Yuggoth is implied to be the same as Pluto, which was discovered around the time Lovecraft was writing the stories.>>