Sotra Patera (named after

Sotra Sotra or Store Sotra is the name of a large island in Øygarden Municipality in Vestland county, Norway, located just west of the city of Bergen. It is part of a pair of islands called 'Sotra' and 'Litlesotra' ('small Sotra') that are part of a ...

island in

Norway Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...

) is a prominent depression on

Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...

, the largest moon of

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; ...

. It was formerly known as Sotra Facula; the current name was approved on 19 December 2012. It is a possible

cryovolcanic A cryovolcano (sometimes informally called an ice volcano) is a type of volcano that erupts volatiles such as water, ammonia or methane into an extremely cold environment that is at or below their freezing point. The process of formation is ...

caldera across and deep, and is immediately to the east of the largest putative cryovolcanic mountain on Titan, the high Doom Mons. Sotra Patera is the deepest known pit on Titan. The ice volcano or cryovolcano Doom Mons forms a roughly circular mountain measuring about across. It has two peaks standing about and high with multiple craters, with Sotra Patera at being the deepest. Finger-like flows are visible on the flanks of the mountain, measuring perhaps thick.Cassini Spots Potential Ice Volcano on Saturn Moon
. NASA, December 14, 2010 Sotra Facula global view

The ''

Cassini–Huygens ''Cassini–Huygens'' ( ), commonly called ''Cassini'', was a space-research mission by NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a space probe to study the planet Saturn and its system, including its ri ...

'' mission has mapped Sotra Patera using the Cassini orbiter's onboard radar instrument and the visual and infrared mapping spectrometer. An earlier survey of the region in 2004 revealed a circular bright spot, or ''facula'', which was nicknamed "The Rose". A subsequent flyby by Cassini re-surveyed the region from a different angle, enabling members of the

US Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, an ...

Astrogeology Science Center to generate

stereoscopic Stereoscopy (also called stereoscopics, or stereo imaging) is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. The word ''stereoscopy'' derives . Any stereoscopic image is ...

mapping of Sotra Patera and the surrounding area. Researchers also discovered at least two more mountains and another big crater, forming a chain of mountains several hundred kilometers long flanked by lava-covered lowlands. With Doom Mons, Sotra Patera is regarded as "the very best evidence, by far, for volcanic topography anywhere documented on an icy satellite", according to planetary scientist Jeffrey Kargel of the

University of Arizona The University of Arizona (Arizona, U of A, UArizona, or UA) is a public land-grant research university in Tucson, Arizona. Founded in 1885 by the 13th Arizona Territorial Legislature, it was the first university in the Arizona Territory. ...

. It has been compared with terrestrial volcanoes such as Etna,

Laki Laki () or Lakagígar (, ''Craters of Laki'') is a volcanic fissure in the western part of Vatnajökull National Park, Iceland, not far from the volcanic fissure of Eldgjá and the small village of Kirkjubæjarklaustur. The fissure is proper ...

and volcanic cones near

Flagstaff, Arizona Flagstaff ( ) is a city in, and the county seat of, Coconino County in northern Arizona, in the southwestern United States. In 2019, the city's estimated population was 75,038. Flagstaff's combined metropolitan area has an estimated population ...

. There is as yet no evidence of current activity, but researchers plan to monitor the area for changes. It is unclear what might have been erupted from Sotra Patera—possibly water mixed with

ammonium The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternar ...

, or more exotic

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...

compounds such as

polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including ...

paraffin wax Paraffin wax (or petroleum wax) is a soft colorless solid derived from petroleum, coal, or oil shale that consists of a mixture of hydrocarbon molecules containing between 20 and 40 carbon atoms. It is solid at room temperature and begins to ...

es or

asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term ...

.Castelvecchi, Davide.
Titan Spews: Discovery of Cold Volcanoes on Saturnian Moon May Solve Methane Mystery
. ''Scientific American'', December 16, 2010 The eruptions may also have brought

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ear ...

to the surface. Titan's dense methane atmosphere is constantly being broken down by sunlight in the upper atmosphere through photolysis; cryovolcanism may therefore explain how the atmosphere is being replenished. The eruptions of Sotra Patera are presumed to originate in a layer of liquid water lying below Titan's icy crust. The mountain's heavily cratered appearance indicates that it must have erupted with considerable force, but the precise mechanism by which this happened is not certain. Liquid water is ordinarily denser than ice but it is possible that the water's density may be reduced by mixing with other substances, such as

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogeno ...

, allowing it to force its way to the surface. Alternatively, some other mechanism such as the underground formation of methane bubbles or a build-up of tectonic pressure may be responsible.

References

{{Titan Surface features of Titan (moon) Extraterrestrial volcanoes