Violent Truth Behind Sun's 'Gentle Giants' Uncovered

Coronal mass ejections are violent explosions that can fling electrified gas [plasma] with a mass greater than Mount Everest towards the Earth with destructive consequences for satellites. They can originate from active regions on the Sun, long known to consist of forests of loops filled with plasma. These active loops are roughly 50,000 km in size. However, active regions on either side of the solar disk are frequently connected by giant loops, which can bridge the Sun's equator. These loops have long been thought of as the gentle giants of the Sun, but in a paper to be published early this year in the journal of Astronomy and Astrophysics, the researchers describe the explosive characteristics of these giants.

An example of a giant loop can clearly be seen in the figure where the width of the arrow represents the size of the Earth. These giant loops of plasma are 450,000 km long - large enough to engulf 40 Earths. If Concorde could fly along one of these loops, it would take nearly 9 days to complete the journey!

Coronal mass ejections are violent explosions that cause all sorts of effects from the destruction of satellites, to the creation of the aurora. These effects are commonly referred to as 'space weather'. Using data taken by the Yohkoh and SOHO satellites studying the Sun, the scientists analysed the giant loops to see how frequently they erupt. In the past only one eruption had been observed and so they have been considered the gentle giants of the Sun that do not explode. The researchers found that not only can these huge structures be thrown away from the Sun, but they can also be heated up by a factor of 5, to temperatures of 14 thousand times the temperature of boiling water. They investigated how the loops explode, and it was found that the longer the loop, the more likely it is to erupt - so these are culprits to watch more carefully in the future!

Alexi Glover, part of the space weather team at the European Space Agency [ESA], explains, "These huge loops have been observed for many years - but their connection with coronal mass ejections is only just being understood. In the future we hope to be able to predict coronal mass ejections before they take place, and step by step we are heading towards that goal."

Because of our increasing reliance on communication and navigation satellites for TV, GPS and national and international security, it is vital that we understand how the Sun can release these explosions.

Dr. Louise Harra of MSSL-UCL says, "Space weather is a rapidly developing field, and a vital key to progress is by understanding in detail the physics of Sun. The UK plays a leading role in solar physics and these new results are helping us make substantial advancements in our understanding of these beautiful, but potentially hazardous, coronal mass ejections."

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Images are available to download from the PPARC website at http://www.pparc.ac.uk/Nw/Press/giant_loops.asp