NASA's Juno spacecraft has spotted the most powerful volcanic eruption ever recorded on Io, Jupiter's moon known for constant volcanic activity. This happened during a flyby on December 27, 2024, when the probe passed about 46,200 miles from the moon's surface and captured data on a massive hot spot in the southern hemisphere.
Background
Io sits close to Jupiter, about the size of Earth's Moon. It orbits the gas giant every 42.5 hours in an elliptical path. This path pulls Io back and forth under Jupiter's strong gravity. The varying pull squeezes the moon like a stress ball. That squeeze creates heat deep inside from friction. The heat melts rock and feeds hundreds of volcanoes on Io's surface. No other place in the solar system has this much volcanic action. Lava plumes shoot high into the air, and ash spreads across the surface. Past missions like Voyager in 1979 first saw these volcanoes. Galileo studied them up close in the 1990s. Now Juno, in its extended mission since 2021, keeps watching Io on every other orbit around Jupiter.
Juno's path takes it near Io regularly. It flew close in December 2023 and February 2024, coming within 930 miles each time. Those passes gave clear views of the moon's wild surface. The December 2024 flyby was farther out, but still picked up strong signals. The spacecraft's tools looked at infrared light, which shows heat from below the surface. This light comes from hot spots where magma pushes up. Io's volcanoes number around 400, and they keep the surface fresh. New lava and ash cover old craters faster than impacts can make them.
Key Details
The Juno Infrared Auroral Mapper, or JIRAM, found the hot spot. JIRAM comes from the Italian Space Agency. It sees infrared light up to 45 miles below Jupiter's clouds, but on Io it spots surface heat. During the flyby, JIRAM saw a bright glow in Io's south pole area. The glow was so strong it overwhelmed the detector. That means extreme heat. Scientists think it came from a few hot spots close together, maybe linked to one big magma chamber underground.
Size and Power
This hot spot covers 40,000 square miles, bigger than Earth's Lake Superior. Lake Superior spans about 31,000 square miles for comparison. The eruption's energy topped 80 trillion watts. That is six times the output of every power plant on Earth combined. The old record came from Loki Patera, a lava lake about 7,700 square miles across. This new one beats it by far. JunoCam, the visible light camera, also saw changes. Colors on the surface shifted around the hot spot compared to earlier flybys. Those shifts point to fresh volcanic flows or ash deposits.
"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."
Juno's principal investigator, Scott Bolton from the Southwest Research Institute in San Antonio, called the data mind-blowing. The flybys keep exceeding expectations. Even from farther away, the signals stood out.
What This Means
This eruption sets a new mark for Io's violence. It could leave marks for a long time, like sulfur deposits or small lava flows. Past big blasts on Io have done that. Pyroclastic materials, which are rock bits from explosions, spread out. Sulfur dioxide from plumes colors the surface. Juno plans another look on March 3, 2025, from even farther. Ground telescopes on Earth might spot changes too. The data helps map how volcanoes work on Io.
Understanding this hot spot goes beyond Io. It shows how gravity shapes rocky worlds. Jupiter's pull, plus tugs from moons Europa and Ganymede, drive the action. This tug-of-war keeps Io stretched and heated. Lessons from Io apply to early Earth or Venus, where volcanoes shaped the ground. It also informs studies of exoplanets near their stars. Those worlds might face similar tidal heating. Juno's finds fill gaps in how moons stay active. The mission now eyes Europa's ice and Ganymede too. But Io's fire keeps drawing attention. Each pass adds pieces to the puzzle of solar system volcanism. Scientists expect more flybys to track if this hot spot grows or fades. The surface changes fast, so repeat views matter.
