Go directly to content
With the JIRAM infrared camera, the Jovian infrared aurora mapper aboard the Jupiter probe Juno, the volcanoes of the innermost large moon, Io, as well as the gas giant’s northern lights, can be observed and analyzed. A team led by Ashley Gerard Davies of NASA’s Jet Propulsion Laboratory in Pasadena, California, has now used image data from several Juno flybys of Io to complete the map of active volcanoes in the area of the polar regions of Io. the Moon, which has previously barely been photographed by previous space probes. The group published their results in the journal Nature Astronomy. As the analysis showed, there are currently 266 warm or hot spots on Io, which are distributed more or less homogeneously across the entire lunar surface. At the poles, especially at the South Pole, there are slightly fewer volcanoes. This could be due to differences in the structure of the rock crust. All volcanoes are thought to be fed by a magma ocean just beneath the solid crust, about 40 kilometers thick.
This means that, unlike Earth, Io is molten, at least in the upper part of its rocky mantle. On Earth, the mantle is solid, but it can deform plastically. Only in the boundary layer between the crust, more precisely the lithosphere, and the Earth’s mantle is there a maximum of one to two percent of molten material in a solid rock in the asthenosphere. On Io, however, the asthenosphere has largely melted.
For their research, the group used image data from the Juno probe, which orbits Jupiter from 2016 to 2022. The spatial resolution of the images is between 151 and 20 kilometers per pixel. Images were captured with JIRAM at a wavelength of 4.8 micrometers. The 266 warm and hot spots have temperatures between -70 and +1160 degrees Celsius. Io’s inactive surface has an average temperature of -140 degrees Celsius.
From the image data, Davies’ team created a global map of Io, on which all active areas are recorded. The heat flow emanating from them can vary by a factor of 10,000 from the weakest, barely detectable hot spots to highly active volcanoes. The coldest hot spots release about 0.01 gigawatts per micrometer of heat, while the hottest release up to 100 gigawatts per micrometer. Overall, Io emits about ten times more heat from its interior than the much larger and more massive Earth.
This enormous heat flow can be attributed to tidal friction. Io Jupiter, like Earth’s moon, always faces the same side as our planet, so it rotates steadily. This means that the duration of an orbit of about 42 hours corresponds exactly to the rotation around its own axis. However, this only applies in an undisturbed system. Due to the gravity of the neighboring moons Europa and Ganymede, Io deviates slightly from its rest position, so the tidal mountains created by Jupiter’s strong gravity move back and forth a little. They are up to 100 meters high in solid rock. For comparison: the tidal mountains created by the Sun and Moon on solid Earth are about half a meter high. Since the orbital periods of Europa and Ganymede are in integer proportion to the orbital period of Io, this moon is literally passed through during each orbit, creating enormous amounts of heat through friction in the rock.
At the end of the year and early February 2024, the Juno space probe will make a special approach to the moon Io. During flybys, the probe ventures up to about 1,500 kilometers from the surface. JIRAM and the JunoCam camera will take numerous razor-sharp images, providing even more information about the volcanic events on Io.