Fossa (planetary nomenclature)

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In planetary nomenclature, a fossa /ˈfɒsə/ (pl. fossae /ˈfɒsiː/) is a long, narrow depression (trough) on the surface of an extraterrestrial body, such as a planet or moon. The term, which means "ditch" or "trench" in Latin, is not a geological term as such but a descriptor term used by the United States Geological Survey (USGS) and the International Astronomical Union (IAU) for topographic features whose geology or geomorphology is uncertain due to lack of data or knowledge of the exact processes that formed them. Fossae are believed to be the result of a number of geological processes, such as faulting or subsidence. Many fossae on Mars are probably graben.