On Io, Jupiter's third largest moon, phenomenal forces within the Tvashtar volcano hurl debris 180 miles into space where it crests in a parabolic plume before hailing back to the satellite's surface. Io has been called the most volcanic object in the known universe, and here Tvashtar is working hard to maintain that designation. But the sharp-eyed Why Files viewer will also notice the simultaneous eruption of Prometheous at nine o'clock on Io's horizon, where a small plume -- a mere 40-miles high -- erupts. A third eruption can be seen by following the moon's “terminator” (the line between day and night) northward from Io's south pole. Not far to the right of this line you'll notice a bright patch on the dark side of the moon. There, pieces of debris from the Masubi volcano are propelled so high they escape the shadow of the moon itself, and for a moment shine in the reflected sunlight of Jupiter.
This image was taken from 1.5 million miles away by the Long Range Reconnaissance Imager (LORRI) on NASA's New Horizon probe in early 2007. Voyager recorded similar activity decades ago, but this image represents the clearest view yet of these cataclysmic events. Io is approximately the size of the Earth's moon. One reason it's studied today is because it is considered to be the planetary body that most closely resembles the nature of Earth during the tumultuous formation of the solar system.
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
