Juno takes temperature of Jupiter's fiery moon Io - Phys.org

What the report says

Phys.Org, publishing a NASA report, says the Juno spacecraft has made the first measurements of temperatures beneath the surface of Io, Jupiter’s intensely volcanic moon. The findings, published in the Journal of Geophysical Research: Planets, are based on two close Juno flybys on Dec. 30, 2023, and Feb. 3, 2024, when the spacecraft passed within about 1,500 kilometers of Io.

The observations came from Juno’s Microwave Radiometer, an instrument originally built to study conditions below Jupiter’s cloud tops. During the mission’s extended phase, scientists used it to examine several Galilean moons. On Io, the instrument detected heat from shallow depths, from a few inches down to tens of feet, showing a temperature increase of more than 40 degrees Fahrenheit within just several feet of the surface, according to NASA researchers cited by Phys.Org.

Scientists outlined two possible interpretations: heat may be moving upward through Io’s crust, or the signal may come from cooling lava flows buried beneath roughly 9 to 11 meters of hardened crust and covering about 10% of the surface at a time. The report says this matters because Io’s heat is driven by tidal forces from Jupiter, a process also relevant to icy moons such as Europa and Ganymede, where internal heating may help sustain subsurface oceans.

The flybys also suggested that much of Io’s terrain, apart from its mountains, is unexpectedly smooth over broad areas and made of low-density material resembling pumice or volcanic ash rather than solid rock. The results add a new way to study how heat moves through rocky and icy worlds beyond Earth.