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Friday, December 7, 2007

Scientists discover sun's solar wind source

Scientists discover sun's solar wind source

By Roger Highfield, Science Editor
Last Updated: 7:01pm GMT 06/12/2007

The source of the "solar wind" blowing from the Sun which can damage satellites, harm computers and disrupt global communications may have been traced by scientists.

the sun's atmosphere
Solar wind is propelled away from the sun as speeds of 2 million miles an hour

Solar wind is a stream of electrically charged gas that is propelled away from the Sun in all directions at speeds of up to 2 million miles an hour.

Bursts of magnetic energy from the Sun sometimes cause changes in the solar wind called "space weather" events, which can interfere with terrestrial telecommunications, navigation systems and electric power grids.

Researchers want to learn more about solar wind, in the hope this information can help them predict or plan for space weather "storms", but how solar wind is formed and powered has been the subject of debate for decades.

Now, new data from the Hinode (Japanese for sunrise) satellite shows "magnetic waves" in the charged particles swirling around in the Sun play a critical role in driving the solar wind into space, according to studies by international researchers published in the journal Science.

The magnetic waves, called Alfvén waves after the Swedish scientist who suggested them in 1942, ripple in the electrically charged gas of particles - plasma - within the Sun and its atmosphere.

They have always been a leading candidate in the formation of solar wind since they can transfer energy for the wind from the Sun's surface up through its atmosphere.

"Until now, Alfvén waves have been impossible to observe because of limited resolution of available instruments," said Alexei Pevtsov, Hinode program scientist, at Nasa Headquarters, Washington.

"With the help of Hinode, we are now able to see direct evidence of Alfvén waves, which will help us unravel the mystery of how the solar wind is powered."

Using Hinode's high resolution X-ray telescope, a team led by Jonathan Cirtain at Nasa's Marshall Space Flight Centre, Huntsville, Alabama, peered into the atmosphere at the Sun's poles and observed record numbers of jets of X-rays, sent out as fountains of rapidly-moving hot plasma.

Cirtain's team observed an average of 240 jets per day, some up to 12,000 miles wide and 600,000 miles long, and conclude that Alfvén waves are being formed at the same time.

"The large number of jets, coupled with the high speeds of the outflowing plasma, lends further credence to the idea that X-ray jets are a driving force in the creation of the fast solar wind."

The mission to understand the Sun has some urgency.

Although our local star is not very active at the moment, the number of solar flares and eruptions will increase until reaching solar maximum in 2011 or 2012.

Some predict the next solar cycle will be the most intense for half a century.

The Hinode spacecraft was launched in September 2006 and has been orbiting Earth along a path that keeps it constantly in view of the Sun to study our local star's magnetic field and how its explosive energy propagates through the different layers of the solar atmosphere.

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