Callisto (Moon)

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  • 8/14/2019 Callisto (Moon)


    Callisto (moon)From Wikipedia, the free encyclopedia


    Image of Callisto obtained in 2001 by NASA'sGalileospacecraft


    Discovered by G. Galilei

    S. Marius[1]

    Discovery date January 7, 1610[1]


    Alternate name(s) Jupiter IV

    Adjective Callistoan, Callistan

    Orbital characteristics

    Periapsis 1 869 000 km[b]

    Apoapsis 1 897 000 km[a]

    Mean orbit radius 1 882 700 km[2]
  • 8/14/2019 Callisto (Moon)


    Eccentricity 0.007 4[2]

    Orbital period 16.689 018 4 d[2]

    Averageorbital speed

    8.204 km/s

    Inclination 0.192 (to localLaplace planes)[2]

    Satellite of Jupiter

    Physical characteristics

    Mean radius 2410.3 1.5 km (0.378 Earths) [3]

    Surface area 7.30 107km2 (0.143 Earths)[c]

    Volume 5.9 1010km3 (0.0541 Earths)[d]

    Mass 1.075 938 0.000 137 1023kg(0.018


    Meandensity 1.834 4 0.003 4 g/cm3[3]


    surface gravity1.235m/s2 (0.126g)[e]

    Escape velocity 2.440 km/s[f]

    Rotation period synchronous[3]

    Axial tilt zero[3]Greek

    Albedo 0.22 (geometric)[4]



    min mean max

    80 5 134 11 165 5

    Apparent magnitude 5.65 (opposition)[5]

  • 8/14/2019 Callisto (Moon)


    Surfacepressure 7.5pbar[6]

    Composition ~4 108 cm3carbon dioxide[6]

    up to 2 1010 cm3molecular oxygen[7]

    Callisto (pronounced /k lsto/,[8]named after the Greekmythological figure

    ofCallisto,Greek: ) is a moon of the planet Jupiter, discovered in 1610 by Galileo Galilei.[1] It is

    the third-largest moonin theSolar System and the second largest in the Jovian system, afterGanymede.

    Callisto has about 99% the diameter of the planet Mercurybut only about a third of its mass. It is the

    fourthGalilean moon ofJupiterby distance, with an orbital radius of about 1,880,000 km.[2] It does not

    form part of theorbital resonancethat affects three inner Galilean satellitesIo, Europa and Ganymede

    and thus does not experience appreciabletidal heating.


    Callistorotates synchronously with its orbitalperiod, so the same face is always turned toward Jupiter. Callisto's surface is less affected by

    Jupiter's magnetosphere than the otherinner satellitesbecause it orbits farther away.[10]

    Callisto is composed of approximately equal amounts ofrock and ices, with a meandensity of about

    1.83 g/cm3. Compounds detected spectroscopically on the surface include water ice, carbon

    dioxide, silicates, and organic compounds. Investigation by the Galileo spacecraft revealed that Callisto

    may have a smallsilicatecoreand possibly a subsurface ocean of liquid water at depths greater than

    100 km.[11][12]

    The surface of Callisto is heavily cratered and extremely old. It does not show any signatures

    ofsubsurface processes such asplate tectonicsorvolcanism, and is thought to have evolved

    predominantly under the influence ofimpacts.[13]Prominent surface features include multi-ring structures,

    variously shaped impact craters, and chains of craters (catenae) and associated scarps, ridges and

    deposits.[13] At a small scale, the surface is varied and consists of small, bright frostdeposits at the tops of

    elevations, surrounded by a low-lying, smooth blanket of dark material.[4] This is thought to result from

    the sublimation-driven degradation of smalllandforms, which is supported by the general deficit of small

    impact craters and the presence of numerous small knobs, considered to be their remnants.[14]The

    absolute ages of the landforms are not known.

    Callisto is surrounded by an extremely thin atmosphere composed ofcarbon dioxide[6] and

    probably molecular oxygen,[7] as well as by a rather intense ionosphere.[15]Callisto is thought to have

    formed by slow accretion from the disk of the gas and dust that surrounded Jupiter after its formation.

    [16] Its slowness and the lack oftidalheating prevented rapid differentiation. The slow convection in the