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Beyond Earthly Skies

Subsurface Ocean of Liquid Water on Callisto

20 May 2015, 22:00 UTC
Subsurface Ocean of Liquid Water on Callisto
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Figure 1: Callisto (bottom left), Jupiter (top right) and Europa (below and left of Jupiter’s Great Red Spot) as viewed in 2000 by NASA’s Cassini spacecraft on its way to Saturn. Credit: NASA/JPL/University of Arizona.Callisto was discovered by Galileo Galilei, an Italian astronomer, in January 1610 along with three other large moons around Jupiter - Io, Europa and Ganymede. These four large moons are known as the Galilean satellites of Jupiter and Callisto is the outermost member. With a diameter of 4,821 km, Callisto is the third largest moon in the Solar System and is nearly as large as the planet Mercury. Callisto orbits far enough from Jupiter that it does not participate in the orbital resonance that the three inner Galilean satellites are in. As a result, Callisto has never experienced any appreciable tidal heating.With a mean density of 1.83 g/cm³, Callisto’s bulk composition is roughly half rocky material and half water-ice. Unlike the three other Galilean satellites, Callisto never got warm enough to fully differentiate into a rocky core and an icy mantle. Instead, Callisto is only partially differentiated, with the proportion of rocky material increasing with depth. Nevertheless, interior models of Callisto based on measurements of its ...

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