Recent findings from NASA’s Juno spacecraft reveal that temperatures are exceeding 20 degrees Celsius just below the surface of Io, the most volcanically active moon in the solar system. This groundbreaking discovery sheds light on the dynamics beneath Io’s crust, offering a glimpse into the workings of this extraordinary celestial body.
Io’s arctic region captured by NASA’s Juno spacecraft on December 30, 2023. Image credit: NASA / JPL-Caltech / SwRI / MSSS / Gerald Eichstädt.
Io, one of Jupiter’s 79 moons, holds the title for the most intense volcanic activity in the solar system.
The immense gravitational forces exerted by Jupiter cause constant expansion and contraction of Io, generating significant internal heat.
Traditionally, heat observations have primarily relied on infrared measurements that only capture surface temperatures.
According to Dr. Scott Bolton, Juno’s principal investigator and a research fellow at the Southwest Research Institute, “Io offers a unique insight into tidal heating, a crucial process that provides energy and heat to celestial bodies far from their parent stars.”
“In Io’s case, this energy not only fuels the most massive volcanic structures in the solar system but could also sustain underground oceans on other moons like Europa and Ganymede.”
“Previously, we could only observe heat escaping at the surface or during eruptions,” Dr. Bolton added. “Now, we can analyze how heat transitions from the interior to the surface.”
Utilizing the Microwave Radiometer (MWR) on NASA’s Juno spacecraft, Dr. Bolton and his research team measured Io’s subsurface temperature for the first time, revealing a significant uptick exceeding 20 degrees Celsius just beneath the surface.
Long-range microwave observations indicate that Io’s surface appears smooth, while deeper layers are less dense than typical solid rock, resembling volcanic ash or pumice.
Temperature gradient map of Io based on data from NASA’s Juno spacecraft’s MWR instrument. The colors represent varying heat outputs, with red indicating the highest levels. Image credit: NASA / JPL-Caltech / SwRI / USGS.
The research team also identified intense endogenous heating within the top few tens of meters of Io’s surface.
Two plausible theories emerge from their findings: heat can either rise steadily through the conductive crust or escape through thinner areas of the crust over lava flows, with hot vents covering about 10% of the surface.
Dr. Bolton noted, “The MWR instrument directly observed Io’s heat output from below the surface, marking a surprising pivotal moment for the study of planetary geology.”
“Our findings suggest that similar observations near volcanoes on Earth using MWR-type instruments could reveal valuable insights into underground temperature gradients, enhancing our understanding of volcanic activity.”
This impactful study will be published in the Geophysical Research Journal: Planets.
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Shannon Brown et al. 2026. Io’s subsurface temperature profile observed by the Juno microwave radiometer. Geophysical Research Journal: Planets 131 (7): e2025JE009622; doi: 10.1029/2025JE009622
Source: www.sci.news
