A Hellacious Two Weeks on Jupiter’s Moon Io



Three massive volcanic eruptions occurred on Jupiter’s moon Io within a two-week period in August of last year. This led astronomers to speculate that such “outbursts,” which can send material hundreds of miles above the surface, might be much more common than they thought.

“We typically expect one huge outburst every one or two years, and they’re usually not this bright,” said Imke de Pater, professor and chair of astronomy at the University of California, Berkeley, and lead author of one of two papers describing the eruptions. “Here we had three extremely bright outbursts, which suggest that if we looked more frequently we might see many more of them on Io.”

Io, the innermost of Jupiter’s four large “Galilean” moons, is about 2,300 miles across (3,630 kilometers). Aside from Earth, it is the only known place in the solar system with volcanoes erupting extremely hot lava like that on Earth. Because of Io’s low gravity, large eruptions produce an umbrella of debris that rises high into space.

De Pater’s long-time colleague and coauthor Ashley Davies, a volcanologist with NASA’s Jet Propulsion Laboratory in Pasadena, California, said that the recent eruptions match past events that spewed tens of cubic miles of lava over hundreds of square miles in a short period of time.

“These new events are in a relatively rare class of eruptions on Io because of their size and astonishingly high thermal emission,” Davies said. “The amount of energy being emitted by these eruptions implies lava fountains gushing out of fissures at a very large volume per second, forming lava flows that quickly spread over the surface of Io.”

All three events, including the largest, most powerful eruption of the trio on Aug. 29, 2013, were likely characterized by “curtains of fire” as lava blasted out of fissures perhaps several miles long.

The papers, one with lead author Katherine de Kleer, a UC Berkeley graduate student, and coauthored by UC Berkeley research astronomer Máté Ádámkovics, and the other coauthored by Ádámkovics and David R. Ciardi of the NASA Exoplanet Science Institute/California Institute of Technology, Pasadena, have been accepted for publication in the journal Icarus.

Ciardi is an astronomer who studies exoplanets, but while imaging at the W. M. Keck Observatory in Hawaii, he took infrared imaging for de Pater that was involved in this research.

“I saw this as a nice opportunity to more closely connect one end of solar system formation/evolution to another,” he said. “Understanding our solar system will help understand all the other systems we are finding and vice versa.”


  1. Io is so close to Jupiter that it is being constantly stretched before its gravity reforms it into a sphere. This generates huge amounts of heat.


    Io is so volcanic because it sits in a gravitational wringer. The side closest to Jupiter is pulled harder than its other, outer side. So Io feels a force stretching it. Io’s own gravity tends to UNstretch it, relaxing it back into a perfect sphere. Its 42-hour orbit is not a true circle, so as Io moves closer to and farther from Jupiter, stretching and relaxing, it gets quite a kneading. Its neighboring moons, Ganymede and Europa and Callisto, also contribute to the strain by locking Io into orbital resonance. All of that activity creates a huge amount of heat.

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    The U.S. Geological Survey is in charge of mapping all the planets, not just Earth. In 2012 it released the first global geologic map of Io, based on the combination of Voyager and Galileo images plus the years of scientific conversation since those missions. This map will be a standard for many decades to come—until a new spacecraft mission or until eruptions erase today’s features, whichever comes first.

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