NASA’s Juno probe revealed the “insides” of the solar system’s most volcanically active object.

Scientists have solved one of the main mysteries of the volcanic activity of Jupiter’s moon Io. They determined the global essence of volcanic processes on this moon, eruptions on which were first noticed 44 years ago by NASA’s Voyager 1 probe. It was generally expected that Io’s interior contained a global ocean of hot magma. New data shows that this is a misconception – each volcano on Io has its own personal “hell.”

There are no signs of a global magma ocean found on Io. Image source: NASA

The content of the interior of a celestial body can be judged by its gravitational field. In this regard, the Earth and Moon have very detailed maps of gravitational disturbances, which helps us calculate the orbits of space missions. Maps of the gravitational fields of the Earth and Moon are created using satellites and measuring their speeds and accelerations under the influence of gravitational forces.

Scientists did the same in the case of mapping Io’s gravitational field. The test body for this was NASA’s Juno probe. During two close flybys of Io in December 2023 and February 2024, the probe came within 1,500 km of the satellite. At this time he maintained contact with the Earth. This means that the radio channel operated on two frequencies. From changes in wavelengths due to the Doppler effect, changes in probe speed (acceleration or deceleration) can be calculated. Thus, Io’s gravity, depending on the contents of its depths, would affect the probe in one way or another. How exactly, scientists were able to calculate and understand what this means.

Calculations and modeling have shown that Io’s mantle at shallow depths (about 50 km) is more elastic-viscous than liquid. If the satellite had a global ocean of liquid magma, the response would be completely different. Liquid magma would react more strongly to Jupiter’s tidal forces, and this would create stronger gravitational disturbances, which would be reflected in the acceleration of Juno during its close flyby of this moon. In Io’s case, hundreds of simultaneously active volcanoes are fed from their own pockets of magma, rather than drawing melt from a common source.

The work done helped to understand that tidal forces are not necessarily so strong as those of Jupiter to stir the depths of the nearest moon into a molten ocean of magma. Obviously, this will help evaluate exoplanets and their geology, as well as evolution. In addition, planetary scientists seem to have to reconsider the possible structure of other close moons of Jupiter and Saturn, which over time will directly affect our space programs.