NASA’s Juno found Io’s temperature rising by more than 40 degrees Fahrenheit within the upper few metres everywhere it sampled—not merely at the volcanic hotspots visible from space. The heat may be flowing broadly through the crust or escaping from young lava and buried vents, giving scientists their first look beneath the surface of a rocky moon.

NASA’s Juno found Io’s temperature rising by more than 40 degrees Fahrenheit within the upper few metres everywhere it sampled—not merely at the volcanic hotspots visible from space. The heat may be flowing broadly through the crust or escaping from young lava and buried vents, giving scientists their first look beneath the surface of a rocky moon.

Juno's microwave radiometer found a steep temperature increase below every region of Io sampled during two flybys, pointing to broad heat flow or concealed young lava and vents.