Io (moon)

Io is a moon of the planet Jupiter. It is Jupiter's third biggest moon with a diameter of 3642 km, slightly bigger than Earth's moon. 

Io has about 400 active volcanos. It is the most volcanically active body in the Solar System. This is due to tidal heating because of friction between Jupiter and the other moons, Callisto, Ganymede, and Europa. Volcanoes erupt massive volumes of silicate lava, sulphur and sulphur dioxide. This constantly changes Io's appearance.  

The picture of Jupiter's moon Io was produced by combining the best images from both the Voyager 1 and Galileo Missions. Superbly detailed Voyager 1 images cover longitudes from 240 W to 40 W and the nearby southern latitudes.

Io has highest density of any moon, the strongest surface gravity of any moon, and the lowest amount of water of any known astronomical object in the Solar System.

Due to the same tidal locking that makes the Moon have the same side always facing Earth, Io always has the same side facing Jupiter. Io is a prolate spheroid, pulled out of round by tidal stress from Jupiter’s gravity.

 References 

Category:Jupiter's moons