<Tr> <Td> Ganymede Jupiter III </Td> <Td> </Td> <Td> </Td> <Td> 7003526820000000000 ♠ 5268. 2 </Td> <Td> 7023148000000000000 ♠ 1.48 × 10 </Td> <Td> 1.942 </Td> <Td> 7006107040000000000 ♠ 1070400 </Td> <Td> 7.155 (4) </Td> <Td> 0.204 </Td> <Td> 0.0011 </Td> </Tr> <Tr> <Td> Callisto Jupiter IV </Td> <Td> </Td> <Td> </Td> <Td> 7003482060000000000 ♠ 4820. 6 </Td> <Td> 7023108000000000000 ♠ 1.08 × 10 </Td> <Td> 1.834 </Td> <Td> 7006188270000000000 ♠ 1882700 </Td> <Td> 16.69 (9.4) </Td> <Td> 0.205 </Td> <Td> 0.0074 </Td> </Tr> <P> Io (Jupiter I) is the innermost of the four Galilean moons of Jupiter and, with a diameter of 3642 kilometers, the fourth - largest moon in the Solar System . It was named after Io, a priestess of Hera who became one of the lovers of Zeus . Nevertheless, it was simply referred to as "Jupiter I", or "The first satellite of Jupiter", until the mid-20th century . </P> <P> With over 400 active volcanos, Io is the most geologically active object in the Solar System . Its surface is dotted with more than 100 mountains, some of which are taller than Earth's Mount Everest . Unlike most satellites in the outer Solar System (which have a thick coating of ice), Io is primarily composed of silicate rock surrounding a molten iron or iron sulfide core . </P>

Of the four galilean moons which is the closest to jupiter