Io

Mosaic of the Voyager Missions

Image Credit: 

NASA/JPL

 

Io is the third largest Galilean moon and the closest to Jupiter. It has vey little water and ice, making it the dryest body in the Solar System. It is mostly rocky material which is reflected in its density, 3.55 g/cm³, comparable to the density of the Moon. It is has a larger diameter than the Moon, with an average radius of 1816 km (the Moon has a radius of 1737 km). It only takes 1.77 days to orbit Jupiter, at a semi-major axis distance of 421,700 km. Io has a very hot surface even though it is at the same distance from the Sun as Jupiter. Why?

The quick and simple answer is that tidal forces from Jupiter's immense gravity pull and squeeze Io, keeping the interior hot. As Io orbits Jupiter, those differential forces from Jupiter, as well as the other Galilean moons, keep the interior hot and molten. As we know from Earth, molten interiors lead to volcanoes on the surface and Io has plenty of those. At least 150 active volcanoes have been observed on Io, erupting continuously.

Jupiter also has a much stronger magnetic field than Earth, so large, that Io itself orbits within its confines. The magnetic field lines actually capture ionized particles from the solar wind also ionizes atoms in the thin atmosphere of Io. This ionizing radiates the surface and helps keep it hot even at its extreme distance from the Sun.

The combination of the volancism and the magnetic field of Jupiter gives Io one of the youngest surfaces in the Solar System. The surface is estimated to be only a million years old and making it a place that would not be fun to visit. Io does have an atmosphere, making it one of the few satellites in the Solar System to have an atmosphere. The atmosphere is composed of mainly sulfur compounds, so would not be a pleasant place to smell, even if you could stand the heat and didn't have to breathe.

A comparable place to Io, and Io is in fact the inspiration for this place, is Mustafar in the Star Wars universe. At the end of Episode III: Revenge of the Sith, Obi-Wan and Anakin fight on the surface of Mustafar which is covered in lava lakes and has a lot of volcanic activity. Mustafar is compressed and pulled in the same way as Io, but with two gas giant planets in neighboring orbits providing the gravity, rather than a gas giant and fellow satellites.

Eruption on the surface of Io

Image Credit:

NASA/JPL/University of Arizona

Plume on the limb of Io

Image Credit:

NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute