NASA’s Juno spacecraft has recorded the first measurements of temperature beneath the surface of Io, the most volcanically active body in the solar system, revealing a significant thermal increase just a few meters below the crust. Data collected during the mission indicates that while the surface maintains average temperatures of -143 °C, the heat rises by more than 20 degrees Celsius—or more than 40 degrees Fahrenheit—at shallow depths.
Precision Microwave Sensing
The findings were made possible by the Microwave Radiometer (MWR), an instrument consisting of six antennas capable of capturing radiation across wavelengths between 1.3 and 51 cm. According to MunicipioSur, a Juno mission scientist at the Southwest Research Institute, the MWR allows researchers to characterize the shallow subsurface of rocky and icy moons by using different wavelengths to explore various depths.
The data was gathered during two specific flybys of the satellite on December 30, 2023, and February 3, 2024. During these encounters, the solar-powered probe approached within 1,500 km of Io’s surface. The MWR measured thermal emissions at depths ranging from a few centimeters to several tens of meters.
Tidal Heating and Geological Hypotheses
Shannon Brown, the lead author of the research at NASA’s Jet Propulsion Laboratory (JPL), stated that the observed temperature gradient is far more pronounced than what solar radiation alone could explain. This subsurface heating is attributed to tidal heating, caused by Jupiter’s massive gravitational pull, which can deform the moon’s surface upward and downward by as much as 100 meters.
Scientists are currently considering two primary hypotheses to explain this thermal variation:
- A constant transfer of heat through the crust, which would be equivalent to releasing up to 30 times more energy than Earth.
- The existence of cooled lava flows located beneath a solid cover between nine and 11 meters thick, potentially covering 10% of the surface.
Unexpected Discoveries and Planetary Context
The ability to probe Io’s volcanic rock was described as an unexpected discovery by NASA scientists. Previously, the Juno mission used similar techniques to explore tens of kilometers beneath the ice layers of Ganymede and Europa, assuming those layers were primarily pure water, which acts as a transparent medium for microwave frequencies.
Beyond thermal data, the measurements revealed that regions away from large mountains are remarkably flat. The data indicates the presence of extensive plains, exceeding 100 kilometers in size, composed of very low-density materials similar to volcanic ash or pumice stone.
Broader Scientific Implications
According to Bolton, Io serves as a unique window into understanding tidal heating across the cosmos. He noted that this process provides essential energy and heat to worlds far from their host stars, not only creating volcanic environments like Io but also enabling the existence of liquid water subsurface oceans on satellites such as Europa and Ganymede.
The project team concluded that these findings have direct applications for terrestrial science. Using similar microwave sensors near Earth’s volcanoes could allow scientists to detect thermal gradients beneath the crust, providing new tools for interpreting geological processes on our own planet.
Worth a look
