Juno Makes First-Ever Measurement of Underground Heat on Jupiter’s Volcanic Moon Io

July 2026. United States.

NASA’s Juno spacecraft has made the first-ever measurement of subsurface temperatures on Io, Jupiter’s moon and the most volcanically active world in the solar system, with the most volcanoes of any body known.

Juno made two close flybys of Io in late 2023 and early 2024, coming within about 1,500 kilometers of the moon and using its Microwave Radiometer (MWR) instrument to detect and measure heat rising from beneath the surface. The results showed that just a few feet below the surface, temperatures jump by more than 20 degrees Celsius — a heat signature too intense to be explained by sunlight alone.

Io’s extreme volcanic activity is driven by a process called tidal heating. Io follows a slightly elliptical orbit around Jupiter, and the planet’s enormous gravity continuously stretches and squeezes the moon, generating far more internal heat than Earth produces. The findings were published in the Journal of Geophysical Research: Planets.

(Sources — NASA JPL, Sci.News, EarthSky)