I came across a news item about Io today that I must have missed over the last couple of weeks, possibly because images have not yet been published. On August 15, using the Keck II telescope on Mauna Kea, astronomer and planetary scientist Dr. Imke de Pater of UC Berkeley spotted a massive volcanic eruption on Io, with a magnitude 100-500 times bigger than any eruptions on Earth in recent decades. According to de Pater, the eruption was “way bigger than anything in recorded history on Earth."
Eruptions of Icelandic volcano Eyjafjallajökull (yes, I'm a linguist and even I gave up on pronouncing it) in April 2010 deposited enough ash and micro particles in the atmosphere to wreak havoc with European air travel for weeks. At the same time, Io is only slightly larger than our own moon, yet it appears to produce volcanic eruptions that dwarf the ones on our planet. Amazingly, those eruptions on Io are happening right now. With over 400 active volcanoes, Io has long been known as "the most volcanically active body in our solar system". We will soon know more about what that actually means.
The most active volcano on Earth is Hawaii’s Kilauea. The recently observed eruption on Io released 17,000 times more energy than Kilauea typically produces. Data and imagery of the eruption on Io will be published in an upcoming paper.
While Io is one of the Galilean moons discovered in 1610, little was known about its features and characteristics until quite recently. In the 1970's, the Pioneer and Voyager probes sent back data during flybys that established Io's active volcanic nature and sulfurous atmosphere.
The image above is based on data collected by NASA's Galileo spacecraft in July 1999 and is NASA's highest resolution look at Io's surface. Unlike many of the bodies in our solar system, Io is free of impact craters, with a young, changing surface. The black pockmarks in the image indicate active volcanoes; darker areas indicate the presence of silicates. The whiter, reflective areas consist of sulfur dioxide ice or frost.
Io is also a kind of giant space battery - generating electric current called the Io flux tube - as the moon's elliptical orbit crosses and interacts with Jupiter's magnetic field lines, in an eternal, delicate yet dramatic dance choreographed around the interplay of tidal forces and magnetic fields. Tidal forces acting on Io are so strong that crust displacements of 330 ft (100 m) have been observed.
Io is excessively hostile to Earthly life forms: Ionizing radiation levels on the surface average about 1 Sv/hr - a dose fatal to humans in a matter of hours. Still, Io is an undeniably beautiful moon:
The above photo was taken by NASA's New Horizon probe in 2007. Europa is in the foreground, with Io in the background. Both moons' night sides are facing New Horizon. Io's surface is illuminated by Jupitershine. Europa is closer to New Horizon and not illuminated by the nearby gas giant. The blue plume visible near Io's north pole shows an eruption of the Tvashtar volcanic region. The filaments discernible within the plume have not yet been explained.