Juno Spacecraft Maps Subsurface Heat of Jupiter's Volcanic Moon Io

NASA's Juno spacecraft has provided unprecedented thermal observations of Jupiter's moon Io, the most volcanically active body in the solar system. In a study published on Wednesday in the Journal of Geophysical Research: Planets, researchers present high-resolution data that maps the moon's internal heat engine, offering insights into its volcanic activity.

Io, slightly larger than Earth's Moon, is caught in a gravitational tug-of-war between Jupiter and its neighbouring moons Europa and Ganymede. This tidal flexing generates immense internal friction and heat, melting the interior into magma that feeds hundreds of active volcanoes.

During recent flybys, Juno's Jovian Infrared Auroral Mapper (JIRAM) instrument captured thermal images of Io, recording heat from lava lakes, fissure eruptions, and volcanic calderas. The Juno Microwave Radiometer (MWR) looked below the surface to measure heat output directly.

Scott Bolton, Juno's principal investigator at Southwest Research Institute in San Antonio, said: 'The surprising discovery that we could see below a rocky moon's surface has important implications for studying Earth's volcanoes.' He added that similar instruments near terrestrial volcanoes might reveal subsurface temperature gradients.

The data show a temperature increase of more than 20 degrees Celsius in the upper few metres below the surface. The long microwave wavelengths indicate that Io's surface is smooth and has a low density, similar to volcanic ash or pumice. 'We detect strong endogenic heating within the upper tens of metres,' the researchers wrote.

Two possible explanations match the data: heat rising steadily through a conducting crust, or heat escaping through scattered patches of thin crust above lava or hot vents covering about 10% of the surface.

Shannon Brown, the lead author at NASA's Jet Propulsion Laboratory, said: 'Io provides a unique window into learning how tidal heating works throughout the cosmos. This process can create the most volcanic body in the solar system and also fuels subsurface oceans on moons like Europa and Ganymede.' She noted that previously scientists could only observe heat escaping at the surface; now they can characterise how heat moves from the interior toward the surface.