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Tuesday, 19 November, 2002, 14:00 GMT
Io blows its top
Io, Nasa
Io, the most volcanically active place known

The most powerful eruption ever detected on any planet in our Solar System has been seen on Io, one of Jupiter's moons.

Io, one of the four large Jovian satellites, is highly volcanic with high-temperature eruptions similar to those on Earth.

The outburst was detected using an advanced optical system on the Keck II telescope in Hawaii. The eruption took place in February 2001, though image analysis has only recently been completed.

"It is clear that this eruption is the most energetic ever seen, both on Io and on Earth," says Frank Marchis of the University of California, US.

"Truly massive"

Adaptive optics employs a technique to remove the distorting effects of atmospheric turbulence - the same effect that makes the stars twinkle - by flexing telescope mirrors fast enough to stabilise and focus the bouncing image.

The 2001 Io eruption was very close to Surt, the site of a large eruption in 1979 that took place between the Voyager 1 and Voyager 2 spacecraft flybys.

"We were lucky to detect the beginning of an outburst eruption," says Imke de Pater, also of the University of California.

The Keck telescope captured images of Io on two days in February 2001.

On the first day, Io was mostly quiet, with visible surface features such as dark calderas and relatively bright areas rich in sulphur dioxide frost. Two days later, however, what seemed a small hot spot on the surface had become a large, bright eruption.

"We observed the same side of the satellite and were amazed to see a very bright eruption that had suddenly appeared," says Marchis.

Sulphur volcano, Nasa
An erupting sulphur volcano
"The Surt eruption appears to cover an area larger than the city of Los Angeles and even larger than the entire city of London," Marchis says.

"The total amount of energy being released by the eruption is amazingly high, with the thermal output from this one eruption almost matching the total amount of energy emitted by all of the rest of Io's other volcanoes included."

"This eruption is truly massive," says Ashley Davies, a scientist at the US space agency's (Nasa) Jet Propulsion Laboratory.

The volcano on Io is far more powerful than any eruption recorded by scientists on Earth, with an estimated eruptive power output of about 78,000 gigawatts. By comparison, the power produced by the last significant eruption of Mount Etna in Italy in 1992 was just 12 gigawatts.

Terrestrial geological records indicate that there may have been some comparably large eruptions many millions of years ago in Siberia and in India, which may have contributed to the demise of the dinosaurs.

Fire fountains

The observations will also help reveal more about the nature of Io, says Lionel Wilson at the Planetary Science Research Group at Lancaster University, UK.

"These results may be the first to allow us to make a good estimate of the volume eruption rate of lava on Io in a large volume eruption with a high eruption rate,"

"Building up statistics on the range of eruption conditions that can occur on Io will allow us to deduce much more about the structure of the crust and mantle than we understand at the moment.

"The observed energy indicates the presence of a vigorous, high-temperature volcanic eruption. The kind of eruption to produce this thermal signature has incandescent fire fountains of molten lava which are kilometres high, propelled at great speed out of the ground by expanding gases, accompanied by extensive lava flows on the surface."

The results are published in the November issue of the planetary sciences journal Icarus.

See also:

17 Jan 02 | Science/Nature
06 Oct 01 | Science/Nature
20 Dec 99 | Science/Nature
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