Callisto (36)

Int

Moon of Jupiter

Astronomical specifications:

Discovery	Jan 7, 1610 by Galileo
Orbital characteristics:
Distance from Jupiter	1,882,700 km
Periapsis	1 869 000 km)
Apoapsis	1 897 000 km
Inclination	deg
Eccentricity	0.0074
Orbital periode about Jupiter	16.689 days
Orbital speed	8.204 km/s
Inclination to Jupiter equator	0.2 deg
Number of moons	none
Rings	none
Physical characteristics:
Radius	2,410 km
Surface area	73,000,000 km²
Volume	5.9 x 10¹⁰ km³
Mass	1.0758 x 10²³ kg
Density	1.834 g/cm³
Equatorial gravity	1.235 m/s²
Escape velocity	2.440 km/s
Rotation period	16.689 days
Axial tilt	0 deg
Surface temperature	134 K
Atmospheric composition	O₂ CO₂

Picture, taken in May 2001, is the only complete global color image of Callisto obtained by Galileo, which has been orbiting Jupiter since December 1995.

Size comparison of Earth, Moon and Callisto

Descriptions:

Callisto, named after the Greek mythological figure of Callisto, is a moon of the planet Jupiter. It was discovered in 1610 by Galileo Galilei. It is the third-largest moon in the Solar System and the second largest in the Jovian system, after Ganymede. Callisto has about 99% the diameter of the planet Mercury but only about a third of its mass. It is the fourth Galilean moon of Jupiter by distance, with an orbital radius of about 1,880,000 km.
Callisto rotates synchronously with its orbital period, so the same hemisphere always faces (is tidally locked to) Jupiter. Callisto's surface is less affected by Jupiter's magnetosphere than the other inner satellites because it orbits farther away.
The surface of Callisto is heavily cratered and extremely old. It does not show any signatures of subsurface processes such as plate tectonics or volcanism, and is thought to have evolved predominantly under the influence of impacts. Prominent surface features include multi-ring structures, variously shaped impact craters, and chains of craters (catenae) and associated scarps, ridges and deposits. At a small scale, the surface is varied and consists of small, bright frost deposits at the tops of elevations, surrounded by a low-lying, smooth blanket of dark material. This is thought to result from the sublimation-driven degradation of small landforms, which is supported by the general deficit of small impact craters and the presence of numerous small knobs, considered to be their remnants. The absolute ages of the landforms are not known.
Callisto is surrounded by an extremely thin atmosphere composed of carbon dioxide and probably molecular oxygen, as well as by a rather intense ionosphere. Callisto is thought to have formed by slow accretion from the disk of the gas and dust that surrounded Jupiter after its formation. Callisto's gradual accretion and the lack of tidal heating meant that not enough heat was available for rapid differentiation. The slow convection in the interior of Callisto, which commenced soon after formation, led to partial differentiation and possibly to the formation of a subsurface ocean at a depth of 100 - 150 km and a small, rocky core.
The likely presence of an ocean within Callisto leaves open the possibility that it could harbor life. However, conditions are thought to be less favorable than on nearby Europa. Various space probes from Pioneers 10 and 11 to Galileo and Cassini have studied the moon. 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.

Exploration:

The Pioneer 10 and Pioneer 11 Jupiter encounters in the early 1970s contributed little new information about Callisto in comparison with what was already known from Earth-based observations. The real breakthrough happened later with the Voyager 1 and 2 flybys in 1979-1980. They imaged more than half of the Callistoan surface with a resolution of 1-2 km, and precisely measured its temperature, mass and shape. A second round of exploration lasted from 1994 to 2003, when the Galileo spacecraft had eight close encounters with Callisto, the last flyby during the C30 orbit in 2001 came as close as 138 km to the surface. The Galileo orbiter completed the global imaging of the surface and delivered a number of pictures with a resolution as high as 15 meters of selected areas of Callisto. In 2000, the Cassini spacecraft en route to Saturn acquired high-quality infrared spectra of the Galilean satellites including Callisto. In February-March 2007, the New Horizons probe on its way to Pluto obtained new images and spectra of Callisto.
Proposed for a launch in 2020, the Europa Jupiter System Mission (EJSM) is a joint NASA/ESA proposal for exploration of Jupiter's moons. In February 2009 it was announced that ESA/NASA had given this mission priority ahead of the Titan Saturn System Mission. ESA's contribution will still face funding competition from other ESA projects. EJSM consists of the NASA-led Jupiter Europa Orbiter, the ESA-led Jupiter Ganymede Orbiter, and possibly a JAXA-led Jupiter Magnetospheric Orbiter.

Callisto missions:

Name	Launch Date	Launch rocket	Weight (kg)	Mission
Pioneer 10 (USA)	03-Mar-72	Atlas-Centaur	258 kg	First successful fly-by of Jupiter.
Pioneer 11 (USA)	06-Apr-73	Atlas-Centaur	259 kg	Jupiter probe. First successful fly-by of Saturn providing detailed view of ring structure.
Voyager 2 (USA)	20-Aug-77	Titan-Centaur	815 kg	Voyager 2 flew by Jupiter on July 9, 1979. Returned pictures and data.
Voyager 1 (USA)	05-Sep-77	Titan-Centaur	815 kg	Fly-by probe of Jupiter and Saturn. Returned pictures and data. Discovered volcanoes on Io, Jupiter ring, new Saturn moons and ring structure.
Galileo	18-Oct-89	Shuttle STS-34	-	Galileo made a close flyby of Callisto on Nov 4, 1996 at 1334 UTC at a distance of 1118 km.
Cassini-Huygens (USA,ESA)	15-Oct-97	Titan-Centaur	5.634 kg	Saturn orbiter (Cassini). In 2000, the Cassini spacecraft en route to Saturn acquired high-quality infrared spectra of the Galilean satellites including Callisto.
New Horizons (USA)	19-Jan-06	Atlas V	478 kg	Pluto-Charon fly-by probe. In February-March 2007, the New Horizons probe on its way to Pluto obtained new images and spectra of Callisto.

Ref.: #98 - update: 27.03.11

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