Overview
- Juno gathered the microwave data during two close flybys that occurred on Dec. 30, 2023, and Feb. 3, 2024, when the spacecraft passed roughly 930 miles (1,500 km) above Io’s Jupiter-facing hemisphere.
- The Microwave Radiometer measured temperatures from a few inches to several meters below the surface and found steep gradients, with subsurface temperatures rising more than 40°F within just a few feet.
- Maps released by NASA show discrete warm anomalies, including a prominent hotspot near Zal Montes Patera that is 18–36°F warmer than surrounding ground, and broader regions of elevated shallow heat.
- Researchers offer two leading explanations: a pervasive conductive background heat flow of about 1–3 watts per square meter, or cooling lava flows capped by roughly 30–35 feet of solid crust that cover part of the surface.
- The findings reveal large smooth, low-density plains of pumice-like volcanic deposits, reshape models of tidal heating and heat transport on moons, and prompt calls for more flybys and modeling to distinguish between the competing hypotheses.