The newly-discovered volcanic hotspot is larger than Earth’s Lake Superior, and belches out eruptions six times the total energy of all the world’s power plants.
“NASA’s Juno spacecraft had two really close flybys of Io during its extended mission,” said Dr. Scott Bolton, a researcher at 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.”
Slightly larger than Earth’s Moon, Io is the most volcanically active body in the Solar System.
It is the innermost of Jupiter’s Galilean moons, which in addition to Io include Europa, Ganymede and Callisto.
Io has more than 400 active volcanoes, which are caused by tidal heating, the result of gravitational forces from Jupiter and other Jovian moons.
During its extended mission, Juno’s trajectory passes by Io every other orbit, flying over the same part of the moon each time.
Previously, the spacecraft made close flybys of Io in December 2023 and February 2024, getting within about 1,500 km (930 miles) of its surface.
The latest flyby took place on December 27, 2024, bringing the spacecraft within about 74,400 km (46,200 miles) of the moon, with Juno’s Jovian Infrared Auroral Mapper (JIRAM) instrument trained on Io’s southern hemisphere.
“JIRAM detected an event of extreme infrared radiance — a massive hotspot — in Io’s southern hemisphere so strong that it saturated our detector,” said Dr. Alessandro Mura, a researcher at 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 support that this is the most intense volcanic eruption ever recorded on Io.”
The team estimates the as-yet-unnamed feature spans 100,000 km2 (40,000 square miles).
The previous record holder was Io’s Loki Patera, a lava lake of about 20,000 km2 (7,700 square miles).
The total power value of the new hotspot’s radiance measured well above 80 trillion watts.
The feature was also captured by the mission’s JunoCam visible light camera.
The researchers compared JunoCam images from the two previous Io flybys with those the instrument collected on December 27.
And while these most recent images are of lower resolution since Juno was farther away, the relative changes in surface coloring around the newly discovered hot spot were clear.
Such changes in Io’s surface are known in the planetary science community to be associated with hot spots and volcanic activity.
An eruption of this magnitude is likely to leave long-lived signatures.
Other large eruptions on Io have created varied features, such as pyroclastic deposits (composed rock fragments spewed out by a volcano), small lava flows that may be fed by fissures, and volcanic-plume deposits rich in sulfur and sulfur dioxide.
Juno will use an upcoming, more distant flyby of Io on March 3 to look at the hot spot again and search for changes in the landscape.
Earth-based observations of this region of the moon may also be possible.
“While it is always great to witness events that rewrite the record books, this new hot spot can potentially do much more,” Dr. Bolton said.
“The intriguing feature could improve our understanding of volcanism not only on Io but on other worlds as well.”