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Callisto Fact Sheet

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What Is Known About Callisto SO FAR

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Voyager 2 Image of Callisto (July 1979)

Table of Contents

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Callisto Summary

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The Galilean Moons
Ganymede, Callisto, Io and Europa

With a diameter of over 4,800 km (2,985 miles), Callisto is the third largest satellite in the solar system (only Ganymede and Titan are bigger), and is almost the size of Mercury. Callisto is the outermost of the Galilean satellites, and orbits beyonds Jupiter's main radiation belts.

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Model of Callisto's Interior

Callisto has the lowest density of the Galilean satellites (1.86 grams/cubic centimeter). Its interior is probably similar to Ganymede except the inner rocky core is smaller, and this core is surrounded by a large icy mantle. Callisto's surface is the darkest of the Galileans, but it is twice as bright as our own Moon.

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Voyager 2 Image (July 1979)

Callisto is the most heavily cratered object in the solar system. It is thought to be a long dead world, with a nearly complete absence of any geologic activity on its surface. In fact, Callisto is the only body greater than 1000 km in diameter in the solar system that has shown no signs of undergoing any extensive resurfacing since impacts have molded its surface. With a surface age of about 4 billion years, Callisto has the oldest landscape in the solar system.

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Voyager Image (1979)

There are no large mountains on Callisto, which is probably due to the icy nature of the satellite's surface. The surface features are dominated by impact craters and rings, and the craters are quite shallow. There are two large "bullseye" structures on Callisto, thought to be the result of a massive impact. The largest structure, Valhalla, has a bright patch 600 km across with rings extending out to almost 3000 km. The other ring structure, Asgard, is about 1600 km in diameter.

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Impact Crater Chains on Callisto (Voyager Images - 1979)

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Closeup of an Impact Crater Chain (Galileo Image - 1996)

Seven impact crater chains have been mapped on Callisto. These chains probably formed when fragments of a comet were split apart by Jupiter's gravity and impacted on Callisto. In a similar scenario, Comet Shoemaker-Levy 9 split into 21 fragments and impacted Jupiter in 1994.

No atmosphere has been detected on Callisto.

The Galileo spacecraft will make three close passes by Callisto during its 2 year orbital tour around Jupiter. The first close encounter occurred November 4, 1996.


Callisto Quick-Look Statistics

 
Discovery:                             Jan 7, 1610 by Galileo Galilei
Diameter (km):                         4,806 
Mass (kg):                             1.077e23
Mass (Earth = 1)                       1.807e-02
Surface Gravity (Earth = 1):           0.127 
Mean Distance from Jupiter (km):       1,883,000 
Mean Distance From Jupiter (Rj):       26.6 
Mean Distance from Sun (AU):           5.203 
Orbital period (days):                 16.68902 
Rotational period  (days):             16.68902 
Density (gm/cm?3)                      1.86 
Orbit Eccentricity:                    0.007 
Orbit Inclination (degrees):           0.281 
Orbit Speed (km/sec):                  8.21 
Escape velocity (km/sec):              2.45 
Visual Albedo:                         0.19
Subsolar Temperature (K)               168
Equatorial Subsurface Temperature (K)  126
Surface Composition:                   Dirty Ice 


The Discovery of the Galilean Satellites

Find out how Galileo Galilei discovered the moons around Jupiter.


Callisto Images


Callisto Animations

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Galileo Flybys

Galileo will be making three close flybys of Callisto during its orbital tour of Jupiter.

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