Jupiter’s moon Io is the most volcanically active world in the Solar System. The gravitational tug-of-war between Jupiter and its other large moons squeezes Io so that its interior is molten. That magma finds its way to the surface in lava lakes and volcanic eruptions. In its latest flyby of the moon, NASA’s Juno mission has just witnessed the biggest yet.
There are over 400 volcanos on Io, the largest for a long while has been Loki Patera, a lava lake of 20,000 square kilometers (7,000 square miles). But during the latest flyby, on December 27, 2024, Juno’s infrared camera JIRAM saw an event so intense that it saturated its detector. An unnamed volcanic feature of over 100,000 square kilometers (40,000 square miles) with a total power estimated from its radiance to be over 80 trillion watts.
“JIRAM detected an event of extreme infrared radiance – a massive hot spot – in Io’s southern hemisphere so strong that it saturated our detector,” Alessandro Mura, a Juno co-investigator from the National Institute for Astrophysics in Rome, said in a statement. “However, we have evidence what we detected is actually a few closely spaced hot spots that emitted at the same time, suggestive of a subsurface vast magma chamber system. The data supports that this is the most intense volcanic eruption ever recorded on Io.”
Juno performed close flybys of Io in December 2023 and February 2024, getting within about 1,500 kilometers (930 miles) of its surface. In this latest flyby last month, Juno was much further away – 74,400 kilometers (46,200 miles) – but the changes were so evident that even the JunoCam could see them from that distance.
Even in visible light, you can tell something is happening on Io!
Image Credit: NASA/JPL-Caltech/SwRI/MSSS Image processing by Jason Perry
“Juno had two really close flybys of Io during Juno’s extended mission,” said the mission’s principal investigator, Scott Bolton of the Southwest Research Institute in San Antonio. “And while each flyby provided data on the tormented moon that exceeded our expectations, the data from this latest – and more distant – flyby really blew our minds. This is the most powerful volcanic event ever recorded on the most volcanic world in our Solar System – so that’s really saying something.”
Juno is flying close to Jupiter tomorrow but it won’t be near Io. The next close pass of Io will happen on March 3, although the spacecraft will be further away from the Moon than it was last month. The team hopes to see long-lived signatures of the eruption to better understand what happened on Io.
“While it is always great to witness events that rewrite the record books, this new hot spot can potentially do much more,” said Bolton. “The intriguing feature could improve our understanding of volcanism not only on Io but on other worlds as well.”
Juno is now in its final months of missions, with its final encounter with Jupiter expected on September 17, 2025.
