Located on
Jupiter
Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandth t ...
's
moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
Callisto Callisto most commonly refers to:
*Callisto (mythology), a nymph
*Callisto (moon), a moon of Jupiter
Callisto may also refer to:
Art and entertainment
*''Callisto series'', a sequence of novels by Lin Carter
*''Callisto'', a novel by Torsten Kro ...
, Valhalla is the largest
multi-ring impact crater
An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...
in the
Solar System
The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...
. It is named after
Valhalla
In Norse mythology Valhalla (;) is the anglicised name for non, Valhǫll ("hall of the slain").Orchard (1997:171–172) It is described as a majestic hall located in Asgard and presided over by the god Odin. Half of those who die in combat e ...
, the hall where warriors are taken after death in
Norse mythology.
Valhalla consists of a bright central region 360 km across, an inner ridge and trough zone, and striking concentric rings extending up to about 1,900 km from the center.
Several large impact craters and
crater chain
A crater chain is a line of craters along the surface of an astronomical body. The descriptor term for crater chains is catena , plural catenae (Latin for "chain"), as specified by the International Astronomical Union's rules on planetary nome ...
s are superimposed on Valhalla. The multi-ring system may have formed as semi-liquid or liquid material underlying the brittle lithosphere punctured by the impactor slumped towards the center of the crater following the impact.
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]
General description
Valhalla is the largest multi-ring basin on Callisto and in the Solar System (with diameter up to 3,800 km). It was discovered by the Voyager probes in 1979–80 and is located on the leading hemisphere of Callisto, in its Jupiter facing quadrant slightly to the north of the equator (at about 18°N latitude and 57°W longitude). From the geological
Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other E ...
point of view Valhalla consists of three zones: the central zone, the inner ridge-and-trough zone, and the outer trough zone.
The inner zone (diameter of about 360 km) is an example of a palimpsest
In textual studies, a palimpsest () is a manuscript page, either from a scroll or a book, from which the text has been scraped or washed off so that the page can be reused for another document. Parchment was made of lamb, calf, or kid skin an ...
: a high albedo circular feature of impact origin. The surface in the central zone is relatively smooth and has a mottled appearance. Many impact craters inside it have dark halos. At the high resolution achieved in some '' Galileo'' images the central part of Valhalla looks like a knobby terrain, where bright knobs are surrounded by dark smooth plains; there is noticeable deficit of small impact craters.
The inner ridge and trough zone surrounds the central palimpsest. The ridges that immediately surround the central zone have steep flanks facing outward. These scarps, when studied at a high resolution, turned out to be discontinuous consisting of a series of small bright knobs surrounded by the smooth dark material. They are obviously very degraded structures. The troughs that are situated further from the center than ridges are sinuous and appear to be graben (about 20 km wide). The inner trough zone extends up to 950 km from the center of Valhalla.
The outer trough zone has a radius of 1500 to 1900 km. Its outer boundary is not well defined. It consists of wide double walled sinuous lineaments ( troughs), which like the inner troughs appear to be graben. Although these grabens are wider (up to 30 km) than those in the inner trough zone, they are severely degraded, and are made of a series of small knobs, much like their inner counterparts. There are no indications of volcanic flows or other signs of endogenic
Endogenous substances and processes are those that originate from within a living system such as an organism, tissue, or cell.
In contrast, exogenous substances and processes are those that originate from outside of an organism.
For example, e ...
activity associated with the graben on the high resolution ''Galileo'' images as was suggested based on the low resolution Voyager images. So, all structures within Valhalla basin have impact or tectonic
Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents ...
origin.
Craters
Several prominent impact crater
An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...
s and catenae are located within Valhalla structure. At the northern margin of it Gomul Catena can be found as well as Egdir and Mimir craters. The catena consists of a linear sequence of impact craters and probably resulted from a break-up of a comet (like comet Shoemaker-Levy 9). To the south of Valhalla there are Sarakka and Nar impact craters; to the east of it (at the boundary between the inner and outer trough zones) are Sculd crater and Svol Catena. To the west of Valhalla another large multi-ring basin—Asgard
In Nordic mythology, Asgard (Old Norse: ''Ásgarðr'' ; "enclosure of the Æsir") is a location associated with the gods. It appears in a multitude of Old Norse sagas and mythological texts. It is described as the fortified home of the Æsir ...
—can be found. The central parts of Valhalla are less cratered than the old plain outside the structure. This indicates that Valhalla is significantly younger than Callisto itself.
Origin
The Valhalla multi-ring structure (like other Callistan multi-ring basins) probably resulted from a giant impact, which punctured the outer ridged lithosphere of the moon and entered the underlying layer consisting of a much softer material. The latter can be warm ice or even a liquid ocean, the existence of which can be inferred from magnetometric data. The formation of a ringed structure is caused by the concentric failure of the brittle outer shell (lithosphere) following the impact, after the soft material underlying the lithosphere flows towards the center to fill the cavity excavated by the impact. The absolute age of the Valhalla structure is not known; however, it is the youngest such feature among the five known multi-ring structures on Callisto. Estimates of its age vary from 2 to 4 billion years.
Consistent with this picture, imaging by the ''Galileo'' spacecraft found no evidence of disruption of the area of Callisto antipodal to Valhalla. Such disrupted terrain normally forms as a result of focusing of the seismic energy at the opposite point after the impact. The absence of such disruption supports the presence of a subsurface ocean, which would have absorbed much of the seismic energy, at the time of Valhalla's formation.
In fiction
Kim Stanley Robinson
Kim Stanley Robinson (born March 23, 1952) is an American writer of science fiction. He has published twenty-two novels and numerous short stories and is best known for his ''Mars'' trilogy. His work has been translated into 24 languages. Many ...
's '' Galileo's Dream'' (2009) contains a detailed description of a large city built around the concentric rings of Valhalla in the 29th century. The same city is briefly mentioned in Robinson's '' 2312''.
See also
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References
{{DEFAULTSORT:Valhalla (Crater)
Surface features on Callisto (moon)
Impact craters on Jupiter's moons