© Katherine de Kleer/UC Berkeley/Gemini Observatory/AURA
Image of Io taken in the near-infrared at the Gemini North telescope on August 29. In addition to the extremely bright eruption on the upper right limb of the satellite, the lava lake Loki is visible in the middle of Io’s disk, as well as the fading eruption that was detected earlier in the month by de Pater on the southern (bottom) limb.
Jupiter's innermost moon, Io - with over 400 active volcanoes, extensive lava flows and floodplains of liquid rock - is by far the most geologically active body in the Solar System. But last August, Io truly came alive with volcanism.

Three massive volcanic eruptions led astronomers to speculate that these presumed rare outbursts were much more common than previously thought. Now, an image from the Gemini Observatory captures what is one of the brightest volcanoes ever seen in our Solar System.

"We typically expect one huge outburst every one or two years, and they're usually not this bright," said lead author Imke de Pater from the University of California, Berkeley, in a press release. In fact, only 13 large eruptions were observed between 1978 and 2006. "Here we had three extremely bright outbursts, which suggest that if we looked more frequently we might see many more of them on Io."

De Pater discovered the first two eruptions on August 15, 2013, from the W. M. Keck Observatory in Hawaii. The brightest was calculated to have produced a 50 square-mile, 30-feet thick lava flow, while the other produced flows covering 120 square miles. Both were nearly gone when imaged days later.

The third and even brighter eruption was discovered on August 29, 2013, at the Gemini observatory by UC Berkeley graduate student Katherine de Kleer. It was the first of a series of observations monitoring Io.
Images of Io
© Katherine de Kleer/UC Berkeley/Gemini Observatory/AURA
Images of Io tracking the evolution of the eruption as it decreased in intensity over 12 days. Due to Io’s rapid rotation, a different area of the surface is viewed on each night; the outburst is visible with diminishing brightness on August 29 & 30 and September 1, 3, & 10.
De Kleer and colleagues were able to track the heat of the third outburst for almost two weeks after its discovery. The team timed observations from Gemini and NASA's nearby Infrared Telescope Facility to coincide with observations by the Japanese HISAKI spacecraft.

This allowed the observations to "represent the best day-by-day coverage of such an eruption," said de Kleer. The team was able to conclude that the energy emitted from the late-August eruption was about 20 Terawatts, and expelled many cubic kilometers of lava.

"At the time we observed the event, an area of newly-exposed lava on the order of tens of square kilometers was visible," said de Kleer. "We believe that it erupted in fountains from long fissures on Io's surface, which were over ten-thousand-times more powerful than the lava fountains during the 2010 eruption of Eyjafjallajokull, Iceland, for example."

The team hopes that monitoring Io's surface annually will reveal the style of volcanic eruptions on the moon, the composition of the magma, and the spatial distribution of the heat flows. The eruptions may also shed light on an early Earth, when heat from the decay of radioactive elements - as opposed to the tidal forces influencing Io - created exotic, high-temperature lavas.

"We are using Io as a volcanic laboratory, where we can look back into the past of the terrestrial planets to get a better understanding of how these large eruptions took place, and how fast and how long they lasted," said coauthor Ashley Davies.

The latest results have been published in the journal Icarus.