Jupiter’s moon Io is the most volcanic world in the Solar System, with over 400 volcanoes. Some of them eject plumes as high as 500 km (300 mi) above the surface. Its surface is almost entirely shaped by all this volcanic activity, with large regions covered by silicates, sulphur, and sulphur dioxide brought up from the moon’s interior. The intense volcanic activity has created over 100 mountains, and some of them are taller than Mt. Everest.
Io is unique in the Solar System, and the Juno orbiter’s JunoCam captured some new images of Io’s abundant volcanic activity.
Io is in a tough position. It’s locked in a kind of gravitational tug-of-war with massive Jupiter and the other Galilean moons, Ganymede, Europe, and Callisto. All that gravitational energy, particularly from Jupiter and Europa, creates friction in the moon’s interior that creates ‘tidal heating.’ That sets it apart from Earth’s volcanism, which is caused largely by the heat from the decay of radioactive isotopes in the mantle, including uranium, potassium, and thorium. In fact, Io produces bout 40% more heat than Earth, an amount that simply cannot be produced by radioactive decay.
This composite image shows how volcanoes dot Io’s surface. It was created with Juno’s JIRAM instrument and its JunoCam instrument. Image Credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM
While Juno’s images of Io are the newest, they’re not necessarily the best. Voyager 1 and Galileo both got closer to Io than Juno did, and their images of the surface are even more stunning.
Galileo captured this image of Io’s surface with a volcano in 1997. Image Credit: NASA/JPL/DLR
But Juno’s much more modern instruments allow it to study Io’s volcanic nature in greater detail. This is important because of some questions scientists would like answers to. Although there’s widespread scientific agreement that tidal heating creates the heat driving all of the moon’s volcanic activity, the heating doesn’t create the volcanoes where we expect them to be, according to our best scientific understanding. One of Juno’s goals is to image the moon’s surface over time to build a more comprehensive picture of the moon’s volcanic activity.
Io has about 115 named mountains, and their average height is about 6,300 m (20,700 ft). Boösaule Montes, at 17,500 metres (57,400 ft) is Io’s tallest moon. Compare that to Mt. Everest’s height of almost 8,850 meters (29,035 ft.) And Io is only 3600 km in diameter, compared to Earth’s 12,700 km diameter. Mountains can be so high on smaller bodies because they have weaker gravity.