Mommur Chasma is the largest 'canyon

Chasma

Chasma is a term used in astrogeology to refer to "a deep, elongated, steep-sided depression". The plural is chasmata. An example is Eos Chasma on Mars. Below are images of some of the major chasmata of Mars...

' on the known part of the surface of Uranus

Uranus

Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...

' moon Oberon

Oberon (moon)

Oberon , also designated ', is the outermost major moon of the planet Uranus. It is the second largest and second most massive of the Uranian moons, and the ninth most massive moon in the Solar System. Discovered by William Herschel in 1787, Oberon is named after the mythical king of the fairies...

. 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

Crust (geology)

In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...

 cracked as a result. The canyon is an example of graben

Graben

In geology, a graben is a depressed block of land bordered by parallel faults. Graben is German for ditch. Graben is used for both the singular and plural....

 (rift valley

Rift valley

A rift valley is a linear-shaped lowland between highlands or mountain ranges created by the action of a geologic rift or fault. This action is manifest as crustal extension, a spreading apart of the surface which is subsequently further deepened by the forces of erosion...

) or scarp

Fault scarp

A fault scarp is the topographic expression of faulting attributed to the displacement of the land surface by movement along faults. They are exhibited either by differential movement and subsequent erosion along an old inactive geologic fault , or by a movement on a recent active fault...

 produced by normal fault(s). The chasma was first imaged by Voyager 2

Voyager 2

The Voyager 2 spacecraft is a 722-kilogram space probe launched by NASA on August 20, 1977 to study the outer Solar System and eventually interstellar space...

 spacecraft in January 1986.

The Gazetteer of Planetary Nomenclature states that Mommur Chasma is named after the forest home of the fairy king Oberon

Oberon

Oberon is a legendary king of the fairies.Oberon may also refer to:-People:* Merle Oberon , British actress* Oberon Zell-Ravenheart , Neopagan activist-Media and entertainment:* Oberon...

 in A Midsummer Night's Dream

A Midsummer Night's Dream

A Midsummer Night's Dream is a play that was written by William Shakespeare. It is believed to have been written between 1590 and 1596. It portrays the events surrounding the marriage of the Duke of Athens, Theseus, and the Queen of the Amazons, Hippolyta...

. In fact, Oberon's home is not named in Shakespeare's play; it appears instead in the French epic Huon of Bordeaux

Huon of Bordeaux

Huon of Bordeaux is the title character of a 13th century French epic with romance elements. He is a knight who, after unwittingly killing Charlot, the son of Emperor Charlemagne, is given a reprieve from death on condition that he fulfill a number of seemingly impossible tasks: he must travel to...

.