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| Discovery | |||||||||
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| Discovered by | Galileo Galilei | ||||||||
| Discovery date | 7 January 1610 | ||||||||
| Designations | |||||||||
| Jupiter IV | |||||||||
| Adjectives | Callistoan, Callistonian | ||||||||
| Orbital characteristics | |||||||||
| Periapsis | 1869000 km | ||||||||
| Apoapsis | 1897000 km | ||||||||
| 1 882 700 km | |||||||||
| Eccentricity | 0.0074 | ||||||||
| 16.6890184 d | |||||||||
Average orbital speed | 8.204 km/s | ||||||||
| Inclination | 2.017° (to the ecliptic) 0.192° (to local Laplace planes) | ||||||||
| Satellite of | Jupiter | ||||||||
| Physical characteristics | |||||||||
Mean radius | 2410.3±1.5 km (0.378 Earths)> | ||||||||
| 7.30×107 km2 (0.143 Earths) | |||||||||
| Volume | 5.9×1010 km3 (0.0541 Earths) | ||||||||
| Mass | (1.075938±0.000137)×1023 kg (0.018 Earths) | ||||||||
Mean density | 1.8344±0.0034 g/cm3 | ||||||||
| 1.235 m/s2 (0.126 g) | |||||||||
| 0.359±0.005 (estimate) | |||||||||
| 2.440 km/s | |||||||||
| synchronous | |||||||||
| zero | |||||||||
| Albedo | 0.22 (geometric) | ||||||||
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| 5.65 (opposition) | |||||||||
| Atmosphere | |||||||||
Surface pressure | 7.5 picobar (7.5×10−10 kPa, 7.4019×10−12 atm) | ||||||||
| Composition by volume | ≈ 4×108 molecules/cm3 carbon dioxide; up to 2×1010 molecules/cm3 molecular oxygen(O2) | ||||||||
Callisto is a moon of the planet Jupiter. It was discovered in 1610 by Galileo Galilei and named after Kallisto. It is the second largest moon orbiting Jupiter, after Ganymede, and the third largest moon in the Solar System.
Callisto is almost the same size as the planet Mercury, being 99% the diameter of the planet, but is much less massive. Of the four Galilean moons of Jupiter, Callisto is the farthest out, with an orbital radius of about 1,880,000 kilometres. It does not form part of the orbital resonance that affects three inner Galilean satellites, Io, Europa and Ganymede. Like the Earth's Moon, Callisto rotates synchronously with its orbital period. This means that one side is always turned toward Jupiter, while the other side never sees the face of the planet. Callisto's surface is less affected by Jupiter's magnetosphere than the seven moons nearer the planet.
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