"Juno had two really close flybys of Io during Juno's extended mission," said Scott Bolton, Juno's principal investigator from the Southwest Research Institute. "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."
Io's extreme volcanic activity is fueled by its close proximity to Jupiter. Roughly the size of Earth's Moon, Io experiences relentless gravitational forces as it orbits Jupiter every 42.5 hours. This gravitational interaction generates immense frictional heating within Io, melting its interior and driving eruptions from an estimated 400 volcanoes on its surface.
JIRAM, designed to study Jupiter's weather layer by capturing infrared light from beneath its cloud tops, has also been repurposed to observe Io and other Jovian moons during Juno's extended mission. The instrument's sensitivity allowed it to detect this massive hot spot during a flyby on Dec. 27, 2024, when Juno was 46,200 miles (74,400 kilometers) away from Io. Previous close flybys in December 2023 and February 2024 provided complementary data, but this latest observation was unprecedented.
"JIRAM detected an event of extreme infrared radiance - a massive hot spot - in Io's southern hemisphere so strong that it saturated our detector," explained Alessandro Mura, a Juno co-investigator from the National Institute for Astrophysics in Rome. "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."
This new feature, spanning an estimated 40,000 square miles (100,000 square kilometers), dwarfs the previous record holder, Loki Patera, a 7,700-square-mile (20,000-square-kilometer) lava lake. The total energy output of this newly discovered hot spot exceeds 80 trillion watts.
Juno's JunoCam also captured visible-light images of the region, comparing recent pictures with those from earlier flybys. Despite being taken from a greater distance, the images revealed clear changes in surface coloration around the hot spot, consistent with volcanic activity. Large eruptions on Io are known to leave behind diverse geological features, such as pyroclastic deposits, lava flows, and sulfur-rich volcanic-plume deposits.
The next opportunity to observe this phenomenon will occur on March 3, 2025, when Juno conducts another flyby of Io. Earth-based telescopes may also assist in tracking changes in the region.
"While it is always great to witness events that rewrite the record books, this new hot spot can potentially do much more," added Bolton. "The intriguing feature could improve our understanding of volcanism not only on Io but on other worlds as well."
Related Links
Juno at NASA
The million outer planets of a star called Sol
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