NASA scientists have achieved a major breakthrough by measuring subsurface temperatures on Jupiter’s moon Io for the first time. Using data from the Juno spacecraft’s Microwave Radiometer (MWR), researchers were able to look beneath Io’s surface and study how heat moves underground, providing fresh insights into the solar system’s most volcanically active moon.
The findings offer a new understanding of Io’s internal heat and could eventually help scientists develop better methods to study volcanic activity on Earth and other planetary bodies.
Until now, scientists primarily relied on infrared observations, which measure heat escaping from a planet or moon’s surface.
Juno’s Microwave Radiometer, however, can penetrate below the surface by detecting microwaves at multiple wavelengths, allowing researchers to observe temperatures from a few inches to several feet underground.
According to Scott Bolton, Juno’s principal investigator at the Southwest Research Institute:
“The Juno Microwave Radiometer directly observed Io’s heat output by looking below the surface.”
He noted that the unexpected ability to study underground temperatures on a rocky moon could eventually improve how scientists monitor volcanoes on Earth.
Io is the most volcanically active object in the solar system because of tidal heating.
As the moon orbits Jupiter, the giant planet’s immense gravity continuously stretches and compresses Io due to its slightly elliptical orbit. This constant flexing generates enormous internal heat that fuels hundreds of active volcanoes across the moon.
During close flybys in December 2023 and February 2024, Juno passed within approximately 930 miles (1,500 km) of Io’s surface.
These encounters enabled scientists to directly measure underground temperatures for the first time.
Lead researcher Shannon Brown of NASA’s Jet Propulsion Laboratory explained that:
- Heat was measured from depths ranging from a few inches to several feet below the surface.
- Temperatures increased by more than 40°F (22°C) within just a few feet underground.
- The observed temperature rise was far greater than what sunlight alone could produce.
Researchers believe Io’s underground heat may reach the surface through two primary mechanisms:
1. Continuous Heat Flow Through Rock
Heat may steadily travel upward through solid volcanic rock.
Scientists estimate this background heat flow at approximately:
- 1–3 watts per square meter
Although relatively modest in one location, this represents an enormous amount of total energy across Io—estimated to be up to 30 times greater than Earth’s average internal heat flow.
2. Buried Lava Flows
Another possibility is the presence of ancient lava flows cooling beneath hardened crust roughly:
- 30–35 feet below the surface
These underground lava fields could currently cover around 10% of Io’s surface.
The same microwave technology has already been used by Juno to study Jupiter’s icy moons:
- Europa
- Ganymede
There, scientists examined ice layers extending tens of miles beneath the surface.
The unexpected success on rocky Io suggests similar instruments could be used to study many other planetary bodies.
Scientists believe tidal heating plays a major role throughout the universe.
Scott Bolton explained that understanding Io helps researchers understand:
- Volcanic worlds
- Ocean-bearing moons like Europa and Ganymede
- Exoplanets orbiting distant stars
The findings may also improve future studies of Earth’s volcanoes by revealing underground temperature patterns that surface observations cannot detect.
Juno also made another unexpected discovery.
Despite Io’s reputation for explosive volcanism, large areas of the moon appear remarkably smooth.
Microwave observations indicate these regions have:
- Very low density
- Surface material resembling volcanic ash or pumice rather than solid rock
Scientists believe this porous material may influence how heat moves through Io’s upper crust.
For decades, scientists could only observe heat escaping from Io’s surface.
NASA’s new measurements now reveal how heat travels beneath the crust before reaching the surface, offering the clearest picture yet of Io’s internal volcanic engine.
The discovery also demonstrates that microwave technology can become a powerful tool for studying hidden geological activity on rocky planets and moons throughout the solar system.
