Chasma

Chasma (plural chasmata) is a term used in planetary geology to describe a broad, elongate, steep-walled trough, canyon, or rift in an extraterrestrial crust. The word is derived from Greek chasma, meaning “opening” or “gulf.” Chasmata are distinguished by their length and linear form, often extending for tens to thousands of kilometers, with walls that rise several kilometers above their floors.

Chasmata form primarily through tectonic extension that creates graben and faults, by subsidence and collapse in volcanic or magmatic settings, or by erosion in certain environments. Their origins can involve a combination of processes, and their appearance varies with the geology and history of the host body.

On Mars, chasmata are especially prominent within large canyon systems such as Valles Marineris, where multiple deep troughs run parallel or branch off from a central trough. Similar elongated troughs and canyons are observed on Venus and other planetary bodies, reflecting common mechanisms of crustal deformation and volcanic activity across the solar system.

Chasmata are analyzed using remote sensing data from orbiting spacecraft, including high-resolution imaging and radar observations, to infer crustal structure, tectonic history, and the sequence of geological events that shaped them. They provide important clues about the thermal and mechanical evolution of planetary surfaces and the palaeogeographic history of their worlds.