Callisto (moon)
Second-largest moon of Jupiter, with a heavily cratered surface.
Callisto is the second-largest moon of Jupiter, after Ganymede, and the third-largest moon in the Solar System, following Ganymede and Saturn's moon Titan. Its surface is the oldest and most heavily cratered in the Solar System, and it may harbor a subsurface ocean of liquid water, making it a candidate for possible future crewed missions.
- discoverers
- Simon Marius and Galileo Galilei
- orbital_period
- about 16.7 Earth days
- density
- 1.83 g/cm³
- notable_for
- oldest and most heavily cratered surface in the Solar System; possible subsurface ocean
Lore & Background
The name Callisto, suggested by Simon Marius soon after discovery, comes from Greek mythology, where Callisto was a nymph associated with the goddess of the hunt, Artemis, and one of Zeus's lovers. The name was attributed to Johannes Kepler by Marius. For a considerable time, the names of the Galilean satellites fell into disfavor and were not revived in common use until the mid-20th century; earlier, Callisto was referred to by its Roman numeral designation Jupiter IV.
Reader's Guide
Callisto is significant as the outermost Galilean moon, with a surface that is the oldest and most heavily cratered in the Solar System, showing no signatures of subsurface processes like plate tectonics or volcanism. Its composition is approximately equal parts rock and ice, with a density of 1.83 g/cm³, the lowest among Jupiter's major moons. Because of its low radiation levels, Callisto has long been considered the most suitable base for possible future crewed missions to study the Jovian system. Various space probes, including Pioneers 10 and 11, Galileo, and Cassini, have studied Callisto.
Did You Know?
- The surface of Callisto is the oldest and most heavily cratered in the Solar System, almost completely covered with impact craters.
- Callisto is not in an orbital resonance like the three other Galilean satellites—Io, Europa and Ganymede—and is thus not appreciably tidally heated.
- Callisto is surrounded by an extremely thin atmosphere composed of carbon dioxide and probably molecular oxygen, as well as by a rather intense ionosphere.
Frequently Asked Questions
What is Callisto?
Callisto is Jupiter's second-largest moon and the outermost of the four Galilean satellites orbiting the gas giant. In the broader Solar System it ranks as the third-largest natural satellite, trailing only Ganymede and Titan.
What is special about Callisto's surface?
Callisto carries the oldest and most densely cratered terrain of any known body in the Solar System, a sign that its interior has been largely geologically quiet for billions of years. Unlike its smoother sibling moons, it shows no evidence of recent resurfacing or tectonic activity.
Could Callisto hide a subsurface ocean?
Evidence suggests a layer of liquid water may exist beneath Callisto's icy crust, though it has not yet been directly confirmed. This possible ocean, combined with its relatively stable radiation environment, makes the moon a candidate for future crewed exploration missions.
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