Juno probe unveils secrets of Io's volcanic fireworks

The moon Io is the third largest natural satellite of Jupiter. Its thin atmosphere consists mainly of sulphur dioxide, and its characteristic yellow, orange, and red colours are a result of being covered in sulphur. Scientists have been captivated by it for a long time, mainly because it resembles our Moon in size and is known as the most volcanically active body in the Solar System - it is covered by around 400 volcanoes which eject lava and gases in nearly constant eruptions.

Scientists from NASA have been studying Io for nearly 44 years. They previously believed that a magma ocean beneath Io's surface was responsible, but now it turns out that is not the case.

Though Io was discovered by Galileo in 1610, volcanic activity on its surface was discovered nearly 400 years later. The first signs of volcanic plumes on Io were detected in 1979 by scientist Linda Morabito from NASA, who was analysing images from the Voyager 1 probe. Since then, scientists, including Scott Bolton from the Southwest Research Institute, have been questioning the mechanisms fuelling these volcanoes from within. In December 2023 and February 2024, the Juno probe conducted close flybys over Io, getting as close as approximately 1,500 kilometres.

As scientists explain, the moon Io is extremely close to Jupiter, and its low orbit means it orbits the gas giant every 42.5 hours. Furthermore, its orbit is elliptical, and as the distance from the planet changes, so does the gravitational force acting on the moon, causing it to be constantly compressed. The result is extreme tidal deformations – friction caused by tidal forces that generate internal heat.

NASA scientists determined that Io's interior is most likely mostly solid, and each volcano on Io has its own chamber of liquid magma, not connected to others. The results obtained from these flybys, from earlier missions, and ground-based telescope measurements indicated the absence of a magma ocean hiding beneath Io's surface.

- Juno’s discovery that tidal forces do not always create global magma oceans does more than prompt us to rethink what we know about Io’s interior– emphasises the lead author of the publication, Ryan Park. As he adds, it also has implications for our understanding of other moons, such as Enceladus and Europa, as well as exoplanets, including super-Earths.

- Our new findings provide an opportunity to rethink what we know about planetary formation and evolution [of planets] - explains the lead author of the publication.

Researchers are hopeful for more discoveries from the Jupiter system that may emerge soon. On 24th November, the probe completed its 66th flyby over Jupiter's cloud tops, and on 27th December, a particularly close approach to the planet will occur. When Juno's orbit is closest to its centre, it will be approximately 3,500 kilometres above the cloud tops.