Overview
- The Juno Microwave Radiometer produced the first direct subsurface temperature measurements of Io, with maps and analysis released by the team in late July 2026.
- The measurements, collected during close flybys on Dec. 30, 2023 and Feb. 3, 2024, show temperatures rising by more than 40°F a few feet below the surface and strong heating within the upper meters of the crust.
- Juno identified a major regional microwave anomaly centered on the Zal Montes Patera complex that lines up with an active lava flow seen by the spacecraft.
- The team offers two explanations that both fit the data: steady conductive heat flow across Io’s crust of about 1–3 watts per square meter, or scattered cooling lava patches capped by roughly 9–11 meters of solid crust covering about 10% of the surface.
- The MWR also shows Io’s broad plains are composed of very low-density volcanic deposits like pumice or fluffy ash, and the unexpected ability to probe below rock could be applied to study Earth volcanoes and subsurface processes on moons such as Europa and Ganymede.