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Solar Wind Whips Up Auroral Storms On Jupiter And Saturn

This is a raw image of Jupiter's auroras taken by the Hubble Space Telescope on 14th December 2000. With increasing latitude (i.e. from the bottom up) we can see the: spot that is magnetically linked to the volcanic moon Io that emits plasma at about 1 tonne per second; the main auroral oval that represents the Jupiter's attempt to keep this emitted plasma rotating at the same speed as itself; and the polar auroras, which may be caused by the interaction with the solar wind. Both the main auroral oval and the polar auroras have been shown to vary with the conditions in the solar wind.
by Staff Writers
Leicester, UK (SPX) Mar 31, 2006
Two new studies of auroras on Jupiter and Saturn have challenged current thinking about the processes that control the biggest light-shows in the solar system it turns out the forces at work are the same that produce polar auroras on Earth.

In the first study, scientists at the University of Leicester compared a series of ultraviolet images of Jupiter's auroras taken by the Hubble Space Telescope with simultaneous measurements by the Cassini spacecraft showing conditions in the solar wind as it flew past the giant planet in December 2000 and January 2001.

The scientists found "a strong correlation" between the strength of the solar wind and the behavior of the Jovian auroras. Until now, scientists had thought Jupiter's auroras were caused by the planet's rapid spin and a stream of material emitted from the volcanic moon Io at the rate of one ton per second.

"The argument is certainly not cut and dried," said team leader Jonathan Nichols. "Previous work by our group has shown that Jupiter's main auroral oval is not caused by the same type of processes that cause the Northern Lights on Earth; however, this new study shows that the auroras located polewards of the main ovals are directly linked to the strength with which the solar wind is blowing - which means that Earth-like processes are causing these polar auroras."

Speaking at a meeting of the Royal Astronomical Society, Nichols said the main oval also shows a direct correlation to solar wind strength a finding that is completely opposite from what had been expected by earlier predictions.

He said the results indicate substantial energy is transferred from the solar wind to the planet, something that also could account for why Jupiter is significantly warmer than expected. The findings could affect hypotheses surrounding other aspects of the Jovian magnetosphere, such as why plasma originating from Io is somehow lost from the system, and what generates Jupiter's huge comet-like magnetic tail.

The second Leicester study, by researcher Sarah Badman, examined Saturn's auroras over three weeks in January 2004. Badman also combined images taken by Hubble with measurements of the solar wind recorded by Cassini as it approached the ringed planet.

Badman collated all available images of Saturn's auroras and determined for the first time their most common shape and position, as well as the occurrence of more unusual features. Her findings corroborate the hypothesis that Saturn's auroras are caused by the explosive release of solar wind energy that is built up and stored in the planet's magnetic field.

Earth's auroras are caused by the interaction of its magnetosphere with the solar wind, a stream of charged particles emitted by the Sun traveling at roughly 1-million miles per hour. Some of the charged particles leak into Earth's magnetic field and are channeled into the upper polar atmosphere, where they glow from their interactions with electrically charged air molecules. The brightness of Earth's auroras depends on the rapidly changing conditions in the solar wind.

Jupiter's magnetosphere is five times larger in diameter than the Sun, and its auroras are up to 100 times brighter Earth's. The main oval auroras are formed by 100-million amps of electric current flowing around the magnetic field and into the atmosphere as a result of Jupiter's attempt to keep plasma emitted from its moon, Io, rotating at the same velocity as the planet. Until now, it has been thought that the system is completely dominated by this rotation, and the energy imparted by the solar wind is negligible by comparison.

Like Jupiter, Saturn also possesses an enormous magnetic field and exhibits bright auroral displays. Images taken by previous spacecraft flybys showed a narrow oval of emissions with some varying brightness. The images taken in January 2004, however, showed several unexpected features, including spirals of aurora around Saturn's pole (compared to the oval shape at Earth), bright blobs of aurora that rotate around the pole, and a unique auroral storm, in which half of the polar region was totally filled-in with very bright auroras.

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Cassini Compiles Best Map Of Jupiter
Pasadena CA (SPX) Mar 28, 2006
This color map of Jupiter was constructed from images taken by the narrow-angle camera onboard NASA's Cassini spacecraft, as it flew by the giant planet on Dec. 11 and 12, 2000, on its way to Saturn.

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