Juno measures heat beneath the surface of volcanic moon Io

NASA’s Juno mission has measured temperatures beneath the surface of Jupiter’s moon Io, revealing strong heating within its shallow crust.

The results use microwave observations from close flybys in December 2023 and February 2024. Unlike infrared measurements of the top surface, different microwave wavelengths can probe material at different depths.

Researchers found a temperature gradient too steep to be explained by sunlight alone. They discuss heat moving through the crust and cooling lava as possible explanations. The measurements also indicate extensive smooth areas with low-density surface material. Together, the findings offer a new view of how tidal heating moves from Io’s interior toward its surface.