[5] 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.

[6][7][8] 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.

[10][11][12] 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 Belton Regio.

[14] The feature was first identified in the initial image, first published on 8 July 2015, of Pluto returned after the New Horizons probe recovered from an anomaly that temporarily sent it into safe mode.

[15][16] Surface features of Pluto were initially given provisional, informal names that are selected from a list generated from an online poll conducted earlier in 2015, along the theme of "creatures related to underworld mythologies.