Volcanic Moon Creates Glowing Aurora Spots on Jupiter

March 20, 2008

Unexpected spots on Jupiter's poles could solve the decades-old mystery of what powers the gas giant's spectacular "hyper-auroras," according to a new study.

Auroras were first spotted on Jupiter in 1979, and astronomers have known since the 1990s that the planet's polar light shows are hundreds of times more powerful than Earth's auroras—with bands and curtains that can get as big as Earth itself.

(See a picture of Jupiter's "Northern Lights on steroids" released last year.)

Scientists think that Jupiter and its fiery moon Io are working in concert to cause these seemingly nonstop auroras.

The volcanic moon creates what's known as the Io footprint: a bright spot followed by smaller spots that are downstream of the flow of charged particles around Jupiter.

Now Bertrand Bonfond of Belgium's Université de Liège and colleagues have seen that Io also causes a faint spot to appear upstream.

The results are surprising because no previous theory predicted upstream spots, Bonfond said.

"Previously we only observed downstream spots, but only half of the configurations of Io in the Jovian magnetic field had been studied," Bonfond said. "Now we have the complete picture."

The team's new model for the footprint was published in the March 15 issue of the journal Geophysical Research Letters.

Waves and Spots

Auroras are powered by the interactions between a planet's atmosphere and an influx of charged particles. (See the colorful patterns of Earth's auroras.)

On Earth these particles come from solar storms, but Jupiter has nearby Io, which has a surface that churns with unmatched volcanic action. (See a picture of volcanic plumes on Io.)

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