Jupiter's third-largest moon, Io, is the most volcanically active body in the solar system, as confirmed by the longest-running observations of the moon's thermal output. The regular eruptions and freely flowing lava put Io at the bottom of anyone's list of great outer space vacation destinations.
Researchers from the University of California, Berkeley, obtained 29 months worth of thermal images of Io's hot spots—regions where hot magma from the moon's mantle is forced up through the surface crust.
"On a given night, we may see half a dozen or more different hot spots," said Katherine de Kleer, a UC Berkeley graduate student who led the observations, in a . "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."
Using near-infrared on the 10-meter Keck II and the 8-meter Gemini North—two of the largest telescopes in the world (fittingly located near the summit of Hawaii's dormant volcano Maunakea)—the Berkeley research team determined the temperatures and specific power outputs of individual eruptions on Io. The team found that hot spots can reach temperatures of more than 1300 Kelvin, or about 1900 degrees Fahrenheit.
The volcanic hot spots also seem to migrate over the moon as time passes. Some eruptions even appeared to trigger volcanic events hundreds of kilometers away, almost a third of the way around the entire moon. (Io is a little more than a quarter of the size of the Earth.)
"While it stretches the imagination to devise a mechanism that could operate over distances of 500 kilometers, Io's volcanism is far more extreme than anything we have on Earth and continues to amaze and baffle us," de Kleer said.
Of the four largest moons that orbit Jupiter—called the Galilean moons after the legendary astronomer who discovered them—Io is the closest to the giant gas planet. Like most moons in the solar system, including ours, Io is tidally locked with its planet, keeping the same side facing Jupiter at all times while in its orbit. Because Io is so close to Jupiter, however, the same gravitational forces that cause one side of the moon to always face the planet are strong enough to heat the interior of the moon, moving around rock and magma to create enough friction to render Io completely covered in powerful volcanoes.
Scientists believe the most powerful volcano on Io, Loki Patera, is a massive subterranean lava lake, some 200 kilometers in diameter. A patera is an irregular crater, usually referring to a volcanic crater, and Loki Patera undergoes a strange phenomenon every year or two when it brightens by more than a factor of 10.
Researchers believe that these intense brightening events occur because of what is called crust overturning—when large portions of the thin crust above the lava lake are heated to the point of collapsing. In fact, the brightening events at Loki Patera appear to follow a circular path, suggesting that a massive wave of lava might travel around the lake and cause the crust above to collapse into the giant pool of molten rock.
Models of Io's volcanic activity originally predicted that the majority eruptions should occur either near the poles or near the equator. This is not, however, what the UC Berkley team ended up seeing over their 29-month observation period. Most of the eruptions were seen at middle latitudes between the equator and the poles, findings that will be presented at the 48th meeting of the American Astronomical Society's Division for Planetary Sciences this afternoon.
"The distribution of the eruptions is a poor match to the model predictions," de Kleer said, "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 strange geologic occurance was observed on Io as well. The circular motion of Loki Patera's massive brightening events, as of 2002, traveled in a counterclockwise direction. More recent observations have seen the brightening events travel in a clockwise direction, suggesting Io still has many geological mysteries left to discover and understand.
Unlike Jupiter's watery moon, Europa, there are no plans to send a spacecraft to Io for close study in the near future. Still, continuing observations using ground-based telescopes will give us a better sense of what is happening on Jupiter's moon of fire.