Yangoor is the largest known

impact crater An impact crater is a depression (geology), depression in the surface of a solid astronomical body formed by the hypervelocity impact event, impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal c ...

on the surface of the Uranian moon

Ariel Ariel may refer to: Film and television *Ariel Award, a Mexican Academy of Film award * ''Ariel'' (film), a 1988 Finnish film by Aki Kaurismäki *, a Russian film directed by Yevgeni Kotov * ''ARIEL Visual'' and ''ARIEL Deluxe'', a 1989 and 1991 ...

. A central-peak impact crater, it is about in diameter and is located approximately from Ariel's south pole. The northwestern edge of the crater was erased by formation of ridged terrain. The crater lacks bright ejecta deposits and was imaged for the first time by the ''

Voyager 2 ''Voyager 2'' is a space probe launched by NASA on August 20, 1977, as a part of the Voyager program. It was launched on a trajectory towards the gas giants (Jupiter and Saturn) and enabled further encounters with the ice giants (Uranus and ...

'' spacecraft in January 1986. The crater is named after a spirit that brings day in

Australian Aboriginal mythology Australian Aboriginal religion and mythology is the sacred spirituality represented in the stories performed by Aboriginal Australians within each of the language groups across Australia in their ceremonies. Aboriginal spirituality include ...

. The name Yangoor was officially approved by the

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

in 1988.

Characteristics

At roughly 78 kilometers in diameter, Yangoor is the largest Arielian crater observed by the ''

'' spacecraft in its 1986 flyby of

Uranus Uranus is the seventh planet from the Sun. It is a gaseous cyan-coloured ice giant. Most of the planet is made of water, ammonia, and methane in a Supercritical fluid, supercritical phase of matter, which astronomy calls "ice" or Volatile ( ...

and its system of moons. The crater is extremely shallow, with most of the crater floor having nearly no measurable depth. The floor of Yangoor exhibits a dichotomy: the southern floor is much deeper, with a depth of roughly , than the northern floor, which only has a depth of less than . Yangoor's crater rim and central peak, by comparison, are much more topographically prominent. The crater rim is largely intact and rises above the surrounding terrain, whilst an elongated central peak complex extends from the center to Yangoor's western rim and rises over 1 kilometer in height. The extreme shallowness of Yangoor is unusual and contrasts with the similarly-sized

Domovoy In the Slavic religious tradition, Domovoy (, literally " he oneof the household"; also spelled ''Domovoi'', ''Domovoj'', and known as , (''Domovik''), (''Domovyk'') and (''Damavik'')) is the household spirit of a given kin. According to th ...

, another Arielian crater. The expected depth for a crater of Yangoor's size is around , requiring some mechanism to reduce the depth of the crater after its formation. Astronomer A. Ruzicka proposed in 1988 that the flat portions of Yangoor represents a cryovolcanic flow burying the original crater floor. Alternatively, the flattened nature of Yangoor may indicate an era of viscous relaxation, where Ariel's crust slowly creeps and flattens out topographical features. A team of planetary scientists led by M. T. Bland modelled viscous relaxation for Yangoor in 2023, concluding that a surface heat

flux Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications in physics. For transport phe ...

of at least 30 mW/m² is required to match observations. This value suggests that Ariel underwent a period of intense

tidal heating Tidal heating (also known as tidal working or tidal flexing) occurs through the tidal friction processes: orbital and rotational energy is dissipated as heat in either (or both) the surface ocean or interior of a planet or satellite. When an objec ...

; as Domovoy is not relaxed, either the period was brief, or Ariel's surface was affected unevenly.

References

{{Moons of Uranus Ariel (moon) Surface features of Uranus' moons