[18] At a small scale, the surface is varied and made up of small, sparkly frost deposits at the tips of high spots, surrounded by a low-lying, smooth blanket of dark material. [10], Like most other regular planetary moons, Callisto's rotation is locked to be synchronous with its orbit. [66][67] The convection in the interior parts of Callisto may be layered, because under the high pressures found there, water ice exists in different crystalline phases beginning from the ice I on the surface to ice VII in the center. In much of the earlier astronomical literature, Callisto is referred to by its Roman numeral designation, a system introduced by Galileo, as Jupiter IV or as "the fourth satellite of Jupiter". [22][66] For Callisto, the outer conductive layer corresponds to the cold and rigid lithosphere with a thickness of about 100 km. [6] Its surface composition is thought to be broadly similar to its composition as a whole. [64] Spectral images taken on 15 and 24 December 2001 were re-examined, revealing a faint signal of scattered light that indicates a hydrogen corona. Future US, Inc. 11 West 42nd Street, 15th Floor, [15][6] Spectral data indicate that Callisto's surface is extremely heterogeneous at the small scale. It is the fourth Galilean moon of Jupiter by distance, with an orbital radius of about 1883000 km. In general, these moons maintain liquid oceans because of the gravitational tug from their large giant planets. Callisto /kəˈlɪstoʊ/, or Jupiter IV, is the second-largest moon of Jupiter, after Ganymede. They imaged more than half of the Callistoan surface with a resolution of 1–2 km, and precisely measured its temperature, mass and shape. [43], The dynamical isolation of Callisto means that it has never been appreciably tidally heated, which has important consequences for its internal structure and evolution. NASA has a mission at Jupiter right now called Juno. [23] Various space probes from Pioneers 10 and 11 to Galileo and Cassini have studied Callisto. Space is part of Future US Inc, an international media group and leading digital publisher. It has a diameter of 2,985 miles (4,800 km), which is only 1% smaller than the planet Mercury. New York, These are unusually shallow and may be a transitional landform to the multi-ring structures, as with the Lofn impact feature. [28], There's no established English adjectival form of the name. It is the most heavily cratered object in the solar system, according to NASA. Jupiter's four largest moons — Io, Europa, Ganymede and Callisto — are also known as the Galilean moons, named after Galileo Galilei, who discovered them in 1610. The surface of Callisto is the oldest and most heavily cratered in the Solar System. [62] At the same time, HST was able to detect condensed oxygen trapped on the surface of Callisto. Callisto is the second largest moon orbiting Jupiter and the third largest moon in the solar system. Those 5–40 km across usually have a central peak. [22] In all realistic models of Callisto the temperature in the layer between 100 and 200 km in depth is very close to, or exceeds slightly, this anomalous melting temperature. Callisto's density and temperature were refined, and images of the surface showed features as small as 1 kilometer per pixel — in other words, a resolution small enough to spot impact craters. [11][12], Callisto is composed of approximately equal amounts of rock and ices, with a density of about 1.83 g/cm3, the lowest density and surface gravity of Jupiter's major moons. Other papers have focused on aspects such as the possible water under its surface, refining the crater counts on its surface, and atmospheric investigations. As mentioned above, small patches of pure water ice with an albedo as high as 80% are found on the surface of Callisto, surrounded by much darker material. Receive mail from us on behalf of our trusted partners or sponsors? In 2018, examinations of archival images taken by the Hubble Space Telescope in 2007 showed Callisto's effect on auroral bursts in Jupiter's atmosphere. The two landslides are about 3 to 3.5 km in length. Formerly proposed for a launch in 2020, the Europa Jupiter System Mission (EJSM) was a joint NASA/ESA proposal for exploration of Jupiter's moons. Valhalla is the largest, with a bright central region 600 kilometers in diameter, and rings extending as far as 1,800 kilometers from the center (see figure). This is connected with the anomalous behavior of ice I phase's melting temperature, which decreases with pressure, achieving temperatures as low as 251 K at 2,070 bar (207 MPa). [24][81], The study proposed a possible surface base on Callisto that would produce rocket propellant for further exploration of the Solar System. Its presence would explain the lack of any signs of the endogenic activity on the Callistoan surface. Distance from Jupiter: It is the outermost of the Galilean moons. Because of its low radiation levels, Callisto has long been considered the most suitable place for a human base for future exploration of the Jovian system. [23] Scientist Torrence Johnson said the following about comparing the odds of life on Callisto with the odds on other Galilean moons:[74]. Visit our corporate site. [9] However, oxygen has not yet been directly detected in the atmosphere of Callisto. You will receive a verification email shortly. Callisto is surrounded by an extremely thin atmosphere composed of carbon dioxide[8] and probably molecular oxygen,[9] as well as by a rather intense ionosphere. Dark material usually lies in the lowlands surrounding and mantling bright features and appears to be smooth. [19] The most likely candidate process is the slow sublimation of ice, which is enabled by a temperature of up to 165 K, reached at a subsolar point. It is known to develop when the temperature is sufficiently close to the melting point, due to the temperature dependence of ice viscosity. [24], Callisto was discovered by Galileo in January 1610, along with the three other large Jovian moons—Ganymede, Io, and Europa. [27], However, the names of the Galilean satellites fell into disfavor for a considerable time, and were not revived in common use until the mid-20th century. [44] Its distance from Jupiter also means that the charged-particle flux from Jupiter's magnetosphere at its surface is relatively low—about 300 times lower than, for example, that at Europa. [66] It is thought to proceed in the so-called stagnant lid regime, where a stiff, cold outer layer of Callisto conducts heat without convection, whereas the ice beneath it convects in the subsolidus regime. [56], The ancient surface of Callisto is one of the most heavily cratered in the Solar System. [78] At the time ESA's contribution still faced funding competition from other ESA projects. Second largest Galilean moon of Jupiter and third largest in the solar system, Callisto's anti-Jovian hemisphere imaged in 2001 by NASA's, Periapsis is derived from the semimajor axis (, Apoapsis is derived from the semimajor axis (. Callisto was discovered in 1610 by Galileo Galilei. This led them to conclude that Callisto had a rocky surface. The large ‘bulls-eye’ at the top is believed to be an impact basin formed early in Callisto's history. The signatures of the other moons were previously spotted in Jupiter's atmosphere, but this new research represented the first time that Callisto's effect was found. Because such a thin atmosphere would be lost in only about 4 days (see atmospheric escape), it must be constantly replenished, possibly by slow sublimation of carbon dioxide ice from Callisto's icy crust,[8] which would be compatible with the sublimation–degradation hypothesis for the formation of the surface knobs. It was the Voyager missions of the late 1970s that really showed us a different picture of the moon. [3] This is significantly larger than the orbital radius—1 070 000 km—of the next-closest Galilean satellite, Ganymede. [76], The next planned mission to the Jovian system is the European Space Agency's Jupiter Icy Moon Explorer (JUICE), due to launch in 2022. [63], Atomic hydrogen has also been detected in Callisto's atmosphere via recent analysis of 2001 Hubble Space Telescope data. Galileo's repeated flybys and higher resolution revealed much more information about Callisto than before. [16] Its surface is completely covered with impact craters. The Cassini spacecraft, which orbited Saturn from 2004 to 2017, uncovered extensive evidence of geysers at its moon, Enceladus. The Medici moons were renamed Io, Europa, Ganymede and Callisto to avoid confusion by the mid-1800s. It takes the moon about seven Earth-days to make one complete orbit of the planet. [74] At 4821 km in diameter, Callisto has about 99% the diameter of the planet Mercury but only about a third of its mass. Arguments for an ocean came from two pieces of evidence, according to NASA. [51][52] It was found that Callisto responds to Jupiter's varying background magnetic field like a perfectly conducting sphere; that is, the field cannot penetrate inside Callisto, suggesting a layer of highly conductive fluid within it with a thickness of at least 10 km. [22], Although Callisto is very similar in bulk properties to Ganymede, it apparently had a much simpler geological history. Callisto is a large moon orbiting Jupiter.

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