Moon of Jupiter · Updated May 2026
Callisto.
Callisto is the outermost Galilean moon and the third-largest moon in the solar system at 4,821 km diameter. Its surface is the most heavily cratered object in the solar system — preserved more or less unchanged for the last 4 billion years. Callisto may host a salty ocean beneath an ice-and-rock crust.
View Jupiter system in 3D →Key facts
Callisto sits outside Jupiter's harshest radiation belts, which has historically made it the leading candidate as a base for crewed missions to the Jupiter system.
About Callisto
Unlike Io, Europa, and Ganymede, Callisto is not in a mean-motion resonance and avoids strong tidal heating. Its interior is only weakly differentiated, suggesting a slow accretion. The Valhalla impact basin, ringed by concentric fractures over 1,800 km across, dominates the leading hemisphere.
How to view Callisto in 3D
Callisto orbits Jupiter in real time inside the interactive viewer. Open the parent body to see the orbital geometry, or use the object browser to fly directly to the moon and observe its rotation, surface, and orbit.
Open the Jupiter system →Sources & methodology
Numbers cross-referenced with the sources below; updated May 2026.