The volcano-covered moon of Jupiter was found to lack a magma ocean beneath its surface.

Io, a moon of Jupiter, is the most geologically active body in the Solar System. Its proximity to the gas giant has significant effects. Due to its slightly elliptical orbit (with an eccentricity of 0.005), the moon experiences deformation from tidal forces. These forces are responsible for maintaining volcanic activity on Io.

Previous studies and calculations have shown that the energy from tidal forces could be sufficient to melt Io's interior and create a magma ocean close to the surface, approximately 50 kilometers deep. The surface of the moon hosts around 400 active volcanoes, indicating that at least some of its internal layers must be in a molten state. However, to directly identify the presence of a liquid layer beneath the surface, data on tidal deformation was needed. Recently, this data has been collected.

The Juno spacecraft approached Jupiter in mid-2016. By June 2024, the probe had completed 62 orbits around the planet. Through the spacecraft's movements, researchers have been able to more accurately calculate the orbits of the moons and the gravitational field of Jupiter.

As part of its extended mission, Juno made two close approaches to Io: in December 2023 and February 2024. The spacecraft came within just 1,500 kilometers of the moon's surface. Only the Galileo spacecraft approached closer 22 years ago. The aim of these new close encounters was to gather data to identify the magma ocean.

By combining new measurements with data from previous observations, an international team of scientists calculated Io's tidal deformation. They then constructed simple computer models of Io: one without an ocean, one with an ocean beneath the surface, and one with an ocean deep within the moon, and compared these models with the obtained measurements.

The findings revealed that the existence of a global ocean beneath the surface does not align with the observational data. It is possible that such a molten layer exists at depths greater than 318 kilometers, but if so, it cannot be the source of magma for volcanic activity. Near the surface, Io's mantle is primarily solid, with molten "islands" that "feed" the volcanoes. The results of the study have been published in the journal Nature.

The strong tidal forces on Io proved insufficient to create a global molten layer near the surface. Tidal heating is considered the main "engine" driving the formation of liquid layers on other bodies in the Solar System, particularly the saline oceans on Europa, a moon of Jupiter, and Enceladus, a moon of Saturn. As the authors of the new study noted, it is necessary to reassess the results of research and calculations regarding the formation of such oceans.