Writing in the journal Nature, the British, French and American team claims that these observations provide the first good evidence that a process known as 'magnetic reconnection' can occur over extended areas in space.

Magnetic reconnection is a physical process in which oppositely directed magnetic fields are annihilated and the energy stored in them is converted to beams of energetic atomic particles. This reconnection process is believed to drive the dynamics of the Earths magnetosphere and is responsible for phenomena such as solar flares and the aurora.

Until now, a full description of reconnection has proved elusive because in-situ observations were only made within the Earth's magnetosphere, the band of space surrounding Earth that protects it from most of the Sun's particles. In this area the thin electrical current sheets in which reconnection occurs extend over a short scale, allowing only evidence of patchy reconnection to be found. Researchers needed observations on a much larger scale to prove that reconnection over distances of thousands of kilometres can occur as predicted.

This evidence was provided in 2002, when the team discovered that reconnection could take place in the solar wind, a stream of particles ejected from the atmosphere of the Sun. Here, unlike in the magnetosphere, the current sheets occur over much greater distances. This gave scientists the opportunity to test the theory of large-scale reconnection.

The first reconnection event detected in the solar wind was experienced by three widely separated spacecraft that found it to be at least 2.5 million km long. In addition, reconnection 'exhaust' was detected over a period of two and a half hours, implying that reconnection must have been sustained over at least that time span.

The team has since identified 27 similar events in the solar wind, strongly suggesting that reconnection is large-scale and steady. Professor Andre Balogh of Imperial College London, an author of the paper, says:

"These findings really are a breakthrough because magnetic reconnection is very difficult to observe. Before now we have had the 'smoking gun' of small-scale events but far from a full picture. Now for the first time we have proof that reconnection can and does occur on scales that make it as important as theoretically predicted".



Source: Imperial College London