Io is Jupiter's innermost Galilean moon that is 2,300 miles wide, approximately the same size as our moon, and is the only place in the solar system (except Earth) where active volcanoes have been observed. The volcanic activity is driven by powerful tidal interactions with the gas giant that squeeze Io's interior, heating it up. Like Earth's volcanoes, molten rock (magma) is then forced through Io's crust intermittently erupting as volcanoes.
Many Io eruptions are surprisingly powerful and, because of the moon's low gravity, can blast debris high into space, forming a huge umbrella.
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"These new events are in a relatively rare class of eruptions on Io because of their size and astonishingly high thermal emission," said co-investigator and volcanologist Ashley Davies, from NASA's Jet Propulsion Laboratory and Caltech, in Pasadena, Calif. "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."
The first of the series of massive eruptions were detected by the near-infrared camera (NIRC2) attached to the Keck II telescope. Keck II is one of a pair of adaptive optics-powered telescopes at the Keck Observatory located atop Hawaii's Mauna Kea summit.
While recording the eruptions that occurred in the moon's southern hemisphere on Aug. 15, 2013, the researchers saw the brightest emanate from a caldera called Rarog Patera, which produced a 50 square-mile, 30 foot-thick lava flow - enough lava to cover Manhattan Island. Another eruption that was generated by the caldera Heno Patera produced a flow covering 120 square miles. Both eruptions generated "curtains of fire" as lava blasted from long fissures in Io's crust.
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Then on Aug. 29, one of the brightest eruptions ever witnessed on Io was detected by the Gemini North telescope and the Infrared Telescope Facility (IRTF), also located atop Mauna Kea. This event was hotter than any volcanic eruption seen on Earth today and is more akin to the eruptions that ravaged our planet in its early evolution.
"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," added Davies.