Jupiter from Io artwork Io the third largest of the moons of Jupiter is also one of the closest kilometres The powerful Jovian gravity powers volcanoes on Io forming surface hotspots so that surface temperatures vary greatly ranging from to degrees Celsius Io has a thin atmosphere of sulphur dioxide and a gravity that is less than a fifth of that on Earth Jupiter a gas giant of hydrogen and helium is the fifth planet from the Sun A moons shadow is seen on Jupiters face Another moon is at centre right