Two weeks of hell on Io

Little Io is the most volcanically active body in the solar system. Last August it made sure we were all aware of that fact with...

Little Io is the most volcanically active body in the solar system. Last August it made sure we were all aware of that fact with three great outbursts spread over just two weeks.

Ever since the twin probes Voyagers I and II passed the Jupiter system in 1979, we've known that the planet's innermost large moon is literally bubbling with activity in the form of volcanic eruptions, fire fountains and sheets of hot lava spilling across its surface.

Eruption of Io's Tvashtar volcano photographed by the New Horizons spacecraft in 2007. The plume reached about 102 miles (165 km) high. With over 400 active volcanoes   activity never ceases, but massive outbursts typically happen every one or two years ... or so it was thought. Last August, to astronomers' surprise, three massive volcanic eruptions occurred on Jupiter's moon Io within a two-week period.


"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."

Only on Io do volcanoes spew lavas as intensely hot- hotter actually - as those found on Earth. Because of the moon's low gravity, rock shot out of Io's volcanoes can reach as high as several hundred kilometers, much higher than Earth's best efforts (60-70 km).

"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,"  said Ashley Davies, volcanologist and colleague of de Pater.

Katherine de Kleer, a UC Berkeley graduate student, determined the temperature of the lavas released in the massive eruptions as likely hotter than lavas on present-day Earth but similar to what's believed to have covered our planet shortly after its formation 4.5 billion years ago. Study of Io's lava flows may help us understand how the surfaces of Earth, Venus and the moon were formed.

With it crazy mix of yellows, oranges and reds, Io's often likened to a pizza, which seems very fitting especially if you've been burned by molten cheese dripping from the edge of your slice. The 'cheese' or lava on Io is molten sulfur and its compounds which give the its spectacular color palette.

Io's volcanic activity is the result of a combination of gravitational forces:  Jupiter's powerful gravity pulls it toward the planet while the moons Europa, Ganymede and Callisto pull it in the opposite direction. The opposing forces squeeze and stretch the hapless moon, causing its crust to rise and fall by 300 feet (100 meters). The tremendous friction generated heats and melts interior rocks to form lava that find its way to the surface through fissures in the crust. You'll have to look hard to find any craters on Io as the crust has been resurfaced time and again by flows of molten rock.


Only about as big as Earth's moon, Io is a clearly a horse of a different color all because it finds itself under very different circumstances.

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