Jupiter questions

The Galilean moons are the four largest moons of Jupiter—Io, Europa, Ganymede, and Callisto. They were first seen by Galileo Galilei in December 1609 or January 1610, and recognized by him as satellites of Jupiter in March 1610.

Like our planet, Europa is thought to have an iron core, a rocky mantle and an ocean of salty water. Unlike Earth, however, Europa's ocean lies below a shell of ice probably 10 to 15 miles (15 to 25 kilometers) thick and has an estimated depth of 40 to 100 miles (60 to 150 kilometers).

NASA is back to one of its favorite hobbies — otherworldly cloud gazing — thanks to the Juno spacecraft currently in orbit around Jupiter. The community's votes have resulted in incredible photos like this one. At the time, the spacecraft was conducting its 16th skim over Jupiter's surface, coming within just 4,400 miles of the top of Jupiter's cloud system.

The geologic activity of Io is the result of tidal heating from friction generated within Io's interior as it is pulled between Jupiter and the other Jupiter's moons. With over 400 active volcanoes, Io is the most geologically active object in the Solar System.

Jupiter's moons, especially Io (spot on the left), are powerful sources of auroras on Jupiter. These arise from electric currents along field lines, generated by a dynamo mechanism due to the relative motion between the rotating planet and the moving moon.