A ridge on a planetary surface; pl.dorsa. The name is not a geological term but is used in the nomenclature of individual features, for example Schiaparelli Dorsum on Mercury.
Geology and Earth Sciences
1. The inner margin of an ammonoid (seeammonoidea) shell; the opposite margin to the venter.
2.(pl. dorsa, wrinkle ridge) An elongated area of high elevation (i.e. ridge) on the surface of an extraterrestrial body.