National Geographic News
A mini-magnetosphere around the largest moon in the solar system leaves a mighty footprint on Jupiter's atmosphere—helping to drive the "hyperauroras" that dance across the planet's poles.
That's one finding in new research that offers unprecedented details on interactions between Jupiter and two of its moons, the giant Ganymede and the volcanically active Io.
On Earth, auroras are created by the interaction of charged particles from the sun with Earth's atmosphere. But at a distance of 483,780,000 miles (778,570,000 kilometers), Jupiter is too far away for the sun to be feeding the planet's polar light shows.
Instead, the moon Io's volcanoes eject a constant flow of particles, which create a donut-shaped ring around Jupiter. As Io ploughs through the ring, it generates magnetic waves that then connect to Jupiter and send particles streaming toward the planet's poles, as seen in the above animation.
In addition, the moon Ganymede is big enough to maintain its own protective magnetic "bubble" even as it orbits inside Jupiter's powerful magnetic field. Scientists have suspected that this mini-magnetosphere might be involved in generating the auroras, but the connection has been unclear.
Energy in Motion
Bright dots known as auroral footprints are thought to show where streams of charged particles from Io and Ganymede are entering Jupiter's atmosphere. These dots move as the moons orbit the planet, creating tails that swirl around the auroras.
Above, sets of pictures show auroral footprints moving across Jupiter's north pole as seen in ultraviolet Hubble Space Telescope pictures taken in March 2007 (blue) and April 2005 (red).
Using thousands of such Hubble pictures, researchers with the University of Liège in Belgium studied the size of both moons' footprints and how changes over time relate to the moons' orbits.
The team found that the size of Ganymede's auroral footprint matches the size of the moon's magnetosphere, confirming its role in Jupiter's auroras.
In addition, the Hubble pictures show that the particles streaming from Io have different energy levels, which suggests that some particles don't lose all their energy when they hit Jupiter and so are able to penetrate deep into the planet's atmosphere, the authors say.
"Each of these auroral structures is telling an ongoing story about vast transfers of energy taking place far away from the planet," team member Denis Grodent said in a statement.
Findings presented this week at the European Planetary Science Congress 2009 in Potsdam, Germany.
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