A Hellacious Two Weeks on Jupiter's Moon Io

NASA | AUGUST 10, 2014

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.

Jupiter's moon Io saw three massive volcanic eruptions within a two-week period last August. Credit: Katherine de Kleer/UC Berkeley/Gemini Observatory

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.

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.

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.

Imke de Pater, professor and chair of astronomy at the University of California, Berkeley, discovered the first two massive eruptions on Aug. 15, 2013, in Io's southern hemisphere, using the near-infrared camera (NIRC2) coupled to the adaptive optics system on the Keck II telescope, one of two 10-meter telescopes operated by the Keck Observatory.

The brightest, at a caldera named Rarog Patera, was calculated to have produced a 50-square-mile (130-square-kilometer), 30-foot-thick (10-meter) lava flow. The other eruption, close to another caldera called Heno Patera, produced flows covering 120 square miles (310 square kilometers).

De Pater discovered a third and even brighter eruption - one of the brightest ever seen on Io - on Aug. 29, using both the Near-Infrared Imager with adaptive optics on the Gemini North telescope on Mauna Kea, and the SpeX near-infrared spectrometer on NASA's nearby Infrared Telescope Facility (IRTF).

De Kleer used the fortuitous detection of this outburst simultaneously at Gemini and the IRTF to show that the eruption temperature is likely much higher than typical eruption temperatures on Earth today, "indicative of a composition of the magma that on Earth only occurred in our planet's formative years," she said.

Volcanoes were first discovered on Io in 1979, and subsequent studies by NASA's Galileo spacecraft, which first flew by Io in 1996, and ground-based telescopes show that eruptions and lava fountains occur constantly, creating rivers and lakes of lava. Only 13 large eruptions were observed between 1978 and 2006, in part because only a handful of astronomers, de Pater among them, regularly scan the moon.

The eruptions on Io are likely similar to those that shaped the surfaces of inner solar system planets such as Earth and Venus in their youth.

Monitoring Io's surface annually will reveal the style of volcanic eruptions there, constrain the magma composition, and accurately map the spatial distribution of the heat flow and potential variations over time. This information is essential to better understand the physical processes involved in the heating and cooling processes on Io.

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