Juno Measures the Heat Below Io's Restless Surface

• NASA's Juno spacecraft used its Microwave Radiometer (MWR) to measure heat flow beneath the surface of Jupiter's moon, Io, for the first time.
• Data revealed that temperatures rise by more than 40°F (approx. 22°C) just a few feet below the surface, a gradient significantly steeper than solar heating alone can explain.
• These findings provide a new window into tidal heating, a fundamental process that fuels volcanic activity on Io and may sustain subsurface oceans on icy moons like Europa and Enceladus.

Io's Geological Profile

• Io is the most volcanically active body in the Solar System, hosting over 400 volcanoes and mountains taller than Mt. Everest.
• Its intense volcanic activity is driven by tidal heating caused by the gravitational pull between Jupiter and its moons Ganymede and Europa.

MWR Findings and Hypotheses

• Originally designed to study Jupiter’s deep atmosphere, the MWR successfully probed several meters into Io's rocky subsurface during recent flybys.
• Researchers proposed two potential explanations for the observed heat flow:
  • A highly conductive crust that distributes internal heat from hotspots or magma flows uniformly across the moon.
  • Thin, cooling crusts covering fresh lava flows from the last five years, which could produce the detected heat signal.
• The surface topography, excluding mountains, is surprisingly smooth across 100 km scales, with material density resembling low-density pumice or fluffy volcanic ash rather than solid rock.

Future Research

• The study demonstrates that multi-frequency microwave radiometry is a powerful diagnostic tool for mapping subsurface thermal and physical states on solid bodies.
• Future efforts will combine MWR data with infrared observations, ALMA data, and geophysical modeling to refine maps of heat flux and understand the moon's global heat budget.