NASA's Juno spacecraft has spotted the most powerful volcanic eruption ever recorded on Io, Jupiter's moon known for constant volcanic activity. This massive event took place in Io's southern hemisphere during a flyby on December 27, 2024. The eruption came from a hotspot bigger than Lake Superior, Earth's largest freshwater lake by area, and released energy equal to six times that of all power plants on Earth combined. Scientists made the find using data from Juno's instruments as the probe continued its long study of the Jupiter system.
Background
Io sits close to Jupiter, the largest planet in our solar system. About the size of Earth's Moon, Io orbits Jupiter every 42.5 hours in an elliptical path. This path pulls the moon closer and farther from the gas giant at different times. Jupiter's strong gravity tugs on Io during these changes, squeezing the moon like a stress ball. The squeezing creates heat deep inside Io through friction. That heat melts rock into magma, feeding hundreds of volcanoes on the surface.
Astronomers have known about Io's volcanoes since the Voyager probes flew by in 1979. Those missions showed a surface covered in dark spots from fresh lava flows and bright areas from sulfur deposits. Today, experts count around 400 active volcanoes on Io. Some spew lava fountains miles high because the moon's gravity is weak. Lava plumes can shoot hundreds of miles into space, painting the thin atmosphere with gas and dust. Io stands out as the most volcanic body in the solar system, far busier than Earth, Venus, or any other place we know.
NASA launched Juno in 2011 to study Jupiter's atmosphere, magnetic field, and storms. The probe arrived in 2016 and has made dozens of close passes, or flybys, around the planet. In 2021, NASA extended the mission to focus more on Jupiter's four big moons: Io, Europa, Ganymede, and Callisto. These flybys bring Juno within thousands of miles of the moons, letting its cameras and sensors collect data. Past close looks at Io happened in December 2023 and February 2024, when the spacecraft came within 930 miles of the surface. Each pass reveals new changes on the moon's battered face.
Key Details
Juno's Jovian Infrared Auroral Mapper, or JIRAM, picked up the eruption. This instrument, built by the Italian Space Agency, sees infrared light from heat sources. On the December 27 flyby, Juno stayed about 46,200 miles from Io, farther than before. Even so, JIRAM recorded a blaze of infrared so bright it overwhelmed the detector. The hotspot covers 40,000 square miles, or 100,000 square kilometers—five times larger than Loki Patera, Io's previous biggest lava lake at 7,700 square miles.
The eruption's power topped 80 trillion watts. For scale, all power plants on Earth together produce about 25 trillion watts on average. This single event on Io put out more than three times that amount. Scientists think the signal came from several hotspots firing at once, linked to a huge underground magma chamber.
Surface Changes
Juno's visible light camera, JunoCam, also captured the area. Team members compared these shots to images from the 2023 and 2024 flybys. The new pictures show lower detail because of the distance, but color shifts stand out around the hotspot. Fresh lava darkened some spots, while sulfur lightened others. These changes match signs of active volcanoes on Io.
"JIRAM detected an event of extreme infrared radiance — a massive hot spot — in Io’s southern hemisphere so strong that it saturated our detector," said Alessandro Mura, a Juno co-investigator from the National Institute for Astrophysics in Rome. "The data supports that this is the most intense volcanic eruption ever recorded on Io."
Scott Bolton, Juno's principal investigator at the Southwest Research Institute in San Antonio, called the data surprising. The flybys have exceeded hopes, he said, with this one setting a new record for Io's violence.
What This Means
This eruption breaks records for Io, already the champion of solar system volcanism. It shows how extreme the moon's geology can get, driven by Jupiter's pull. The hotspot might link to a vast magma system below ground, hinting at processes we see hints of on Earth but on a smaller scale. Studying it could explain why Io has so many volcanoes and how they cycle between quiet and explosive phases.
The find helps compare Io to other worlds. Earth's volcanoes, like those in Hawaii or Iceland, come from tectonic plates or hot spots. Venus has shield volcanoes similar to Io's in shape. But no place matches Io's output. Lessons from this event might apply to early Earth or exoplanets around other stars with tidal heating.
Juno plans another flyby of Io on March 3, 2025, from even farther away. The team will check the hotspot for changes, like cooling lava or new flows. Ground telescopes on Earth might spot it too, adding more data. Long-term, these observations track how eruptions reshape Io's surface over time. The moon's volcanoes also feed Jupiter's thin ring and affect its magnetosphere by spitting out charged particles.
"This is the most powerful volcanic event ever recorded on the most volcanic world in our solar system — so that’s really saying something," Bolton said.
Future missions could build on Juno's work. Proposed landers or orbiters might sample Io's lava up close, testing ideas about its makeup. For now, this record eruption reminds us how wild our solar system stays, even billions of miles away. Scientists keep watching, ready for the next surprise from Jupiter's fiery neighbor.
