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Wobbly sun causes plasma jets

127-year-old mystery solved

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A group of scientists has come up with a new explanation for the origins of spicules - jets of plasma that shoot up from the solar surface at speeds of around 90,000 kilometres per hour: the solar matter is propelled into space by sound waves entering the solar atmosphere.

Using observational data from two satellites (TRACE and SOHO) and an the Swedish Solar optical telescope, scientists at Sheffield university and the Lockheed Martin Solar and Astrophysics lab, have determined that the jets occur periodically, about every five minutes or so.

Professor Erdélyi von Fáy-Siebenbürgen then developed a computer simulation of the events, incorporating the effects of compression waves, or sounds waves, in the sun. He explained that the compression waves are most likely caused by two things: the oscillation of the sun itself, and convection cells - areas of rising and falling solar matter. Convection cells on Earth cause thermals, breezes, thunderstorms and other weather patterns. In the sun, they cause compression waves..

The compression waves are usually damped before they reach the solar atmosphere, von Fáy-Siebenbürgen said, but occasionally they get through. When this happens, the compression of the atmosphere forms a shock wave, propelling matter upwards in the form of a plasma jet. The research solves an astrophysical puzzle that has baffled scientists for over 120 years since the spicules were first discovered.

His model produced jets at virtually identical intervals: "I would say it is around 99 per cent accurate," he told The Register today. "We were very surprised by the accuracy of the model. It is something we are very proud of," he said.

Although relatively small compared to full scale solar flares, spicules are interesting for the same reasons: they may contribute to the solar wind. This flow of highly charged particles causes the Aurorae Borealis and Australis, but can also knock out satellites and even bring down electrical systems on Earth during particularly vigarous solar storms. ®

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