Voyager 2 image of Oberon showing Mommur Chasma near the limb at upper right.
Mommur Chasma is the largest 'canyon' on the known part of the surface of Uranus' moon Oberon. This feature probably formed during crustal extension at the early stages of moon's evolution, when the interior of Oberon expanded and its ice crust cracked as a result. The canyon is an example of graben (rift valley) or scarp produced by normal fault(s). The chasma was first imaged by Voyager 2 spacecraft in January 1986.
^Croft, S.K. (March 1989). New Geologic Maps of the Uranian Satellites Titania, Oberon, Umbriel and Miranda. Proceeding of Lunar and Planetary Sciences20 (Lunar and Planetary Sciences Institute, Houston): 205C. Bibcode:1989LPI....20..205C.