Juno Measures the Heat Below Io's Restless Surface

NASA’s Juno spacecraft is providing a clear look beneath the surface of Io, Jupiter’s most volcanic moon. While the mission was originally designed to study the gas giant's atmosphere, engineers repurposed the onboard Microwave Radiometer to gather data on the moon’s crust. This instrument allowed researchers to measure thermal emissions from several feet below the surface during recent flybys.

The findings confirm a significant heat gradient that solar radiation cannot explain. Data shows that temperatures rise by roughly 40 degrees Fahrenheit just a few feet into the ground. Scientists suggest this temperature spike indicates the moon is leaking heat across its entire surface rather than only through concentrated volcanic hotspots.

Researchers are currently evaluating two primary theories for this thermal activity. The first theory suggests the crust is highly conductive, distributing heat from magma flows across the moon at a rate 30 times higher than the Earth's average. The second possibility involves a vast network of recent lava flows capped by thin, cooling layers of volcanic rock.

Beyond these temperature readings, the data reveals surprising physical characteristics about the lunar landscape. Despite its reputation for extreme topography and massive volcanoes, large portions of Io appear relatively smooth. The surface material is porous, behaving more like volcanic ash or pumice than solid rock. This insight into how heat moves from the interior to the surface provides a template for understanding tidal heating on other moons in the solar system, including Europa and Ganymede.

This work highlights the versatility of space instrumentation. By applying microwave radiometry to rocky surfaces, scientists have established a new method for characterizing the interiors of planetary bodies. Future missions will likely incorporate specialized versions of this technology to map heat flow and internal composition on a wider range of targets in the cosmos.