Magnetic Reconnection in Turbulent Plasma Fields Above Earth

A European Space Agency study has discovered experimental evidence of magnetic reconnection occurring in turbulent plasma fields surrounding the Earth.

Plasma turbulences are caused by an irregular behavior of particle flows and magnetic fields within which many small-scale boundaries can form.

Our first line of defense against the incessant flow of solar particles, the Earth's magnetic field, deflects most of this material around the Earth's magnetosphere. This is marked by a boundary layer called the magnetopause. As for any other planet which has a planetary magnetic field (for example Jupiter and Saturn), solar wind is decelerated from supersonic to subsonic speeds by a shock wave (called the 'bow shock') located in front of the magnetopause.

The region between the bow shock and the magnetopause is called the magnetosheath, one of the most turbulent environments in near-Earth space, but in the same time, a more accessible region to study, compared to the solar atmosphere.

Using measurements obtained by the four ESA Cluster satellites, the researchers -- led by Alessandro Retino of the Swedish Institute of Space Physics in Uppsala, Sweden -- confirmed predictions of such reconnections.

Observing reconnection at small-scale boundaries in space requires simultaneous measurements by at least four spacecraft flying in close formation. With an inter-spacecraft distance of only 100 kilometres, the four Cluster satellites observed reconnection within a very thin current 'sheet' embedded in the turbulent plasma with a typical size of about 100 kilometres.

This newly observed type of small-scale reconnection seems to be associated with the acceleration of particles to energies much higher than their average, which could explain, in part, the creation of high energy particles by the Sun.

As "magnetic reconnection, turbulence and shocks are three fundamental ingredients of the plasma Universe" - Philippe Escoubet, Cluster and Double Star Project scientist at ESA - applications of this new find range from the dissipation of magnetic energy in fusion devices on Earth to the understanding of the acceleration of high energy particles in solar explosions called solar flares.