Juno Maps Subsurface Heat on Jupiter’s Moon Io

Overview

• During close flybys on Dec. 30, 2023, and Feb. 3, 2024, Juno’s Microwave Radiometer probed roughly 2–6 meters below Io’s surface and found temperatures rising by more than 40°F several feet down.
• The team mapped distinct microwave heat anomalies, including a prominent hotspot that lines up with an active lava flow at the Zal Montes Patera complex.
• Data support two main explanations: a steady conductive heat flow estimated at about 1–3 watts per square meter across much of Io or cooling lava flows capped by roughly 9–11 meters of solidified crust covering part of the surface.
• Away from mountains, the MWR shows expansive low-density plains that behave like pumice or fluffy volcanic ash rather than solid rock, changing how scientists think about Io’s surface structure.
• The measurements, published July 22, 2026, open a new way to study tidal heating on volcanic and icy worlds and will drive follow-up work to distinguish the competing heat-flow explanations.