Io's volcanism is unmatched by any other rocky body in the solar system. As Jupiter's innermost and third-largest moon, it is at the mercy of the gas giant's powerful tides. As a result, it is constantly erupting, unleashing incredibly powerful explosions, spewing molten rock all over its tortured surface.
Now, astronomers have been able to gather observations of the 2,000 mile-wide Io with two of the world's most powerful telescopes, watching it burn over two years.
"On a given night, we may see half a dozen or more different hot spots," said Katherine de Kleer, of UC Berkeley who led the 29 months of near-infrared observations using the 10-meter Keck II and the 8-meter Gemini North telescopes atop Mauna Kea in Hawaii. It is perhaps a little poetic that Mauna Kea is also a volcano, albeit a dormant one. "Of Io's hundreds of active volcanoes, we have been able to track the 50 that were the most powerful over the past few years."
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As Io orbits Jupiter, slight changes in the moon's orbital distance can cause pretty dramatic changes in the tidal forces it experiences, causing friction from tidal heating. This mechanism delivers a huge amount of energy to Io's interior, keeping it in a molten state and driving perpetual volcanism.
By observing Io for so long, de Kleer's team was able to test some of the theoretical models that are thought to best describe the moon's eruptions. According to theory, the majority of the eruptions should be located either near the poles or the equator and, as Io is tidally locked to Jupiter, the pattern of volcanoes should be symmetrical between the forward-facing and rear-facing (to the direction of its orbit) hemispheres.
But on analyzing 100 days-worth of observations between August 2013 and December 2015, they found a surprising number of powerful, but short-lived eruptions all occurred on the rear-facing hemisphere and at higher latitudes than longer-lived eruptions.
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"The distribution of the eruptions is a poor match to the model predictions," de Kleer said in a statement, "but future observations will tell us whether this is just because the sample size is too small, or because the models are too simplified. Or perhaps we'll learn that local geological factors play a much greater role in determining where and when the volcanoes erupt than the physics of tidal heating do."
Another interesting finding focused on Loki Patera, Io's longest-living volcano that is believed to be a vast lake of molten lava. Every 2 years or so, it is believed the lava lake's cooling crust overturns, much like lava lakes that are found on Earth, triggering an intense brightening, and sending a wave of heat emissions around the lake. This causes destabilization and sinking of more crust and further heating.
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None of these incredibly detailed observations would have been possible without Keck and Gemini's adaptive optics, however. Both observatories use the sophisticated system to manipulate their primary mirrors to compensate for high-altitude turbulence in Earth's atmosphere. Without this compensation, Io would appear too blurry for the observatories to resolve the individual eruption events.
"These remarkable images illustrate the great strides that have been made in high-resolution imaging from the ground over the past decade," said Chris Davis, program director for the Gemini Observatory at the National Science Foundation. "It is amazing to think that, with adaptive optics on 8- to 10-meter-class telescopes like Gemini and Keck, we are now able to resolve features on the surfaces of not just neighboring planets, but their moons as well."
WATCH VIDEO: How Long Can Volcanic Eruptions Last?