The second-largest satellite of Jupiter, and the outermost of the four Galilean satellites; also known as Jupiter IV. It orbits 1 883 000 km from Jupiter's centre in 16.689 days, keeping the same face turned towards the planet. Callisto is 4821 km in diameter but, at magnitude 5.7, is the faintest of the Galilean satellites, because of its low albedo of 0.19. Callisto's density is 1.83 g/cm3. It has an icy surface uniformly covered with impact craters (the largest, Heimdall and Lofn, are 210 and 200 km wide respectively), with little sign of the tectonic resurfacing activity seen on the other Galilean satellites. It has several multi-ringed basins, the two largest being Valhalla (3000 km across, the largest in the Solar System) and Asgard (1400 km across), which are surrounded by numerous concentric rings.
Subjects: Earth Sciences and Geography — Astronomy and Astrophysics.