How solar wind breaks through earth's magnetic field

A wind of charged particles blows outwards from the sun, carrying a magnetic field with it and sometimes this solar wind can break through the earth's magnetic field.

Researchers believe they now have an answer to how this actually happens.

When two areas with plasma (electrically charged gas) and magnetic fields with different orientations collide, the magnetic fields can be "clipped off" and "reconnected" so that the topology of the magnetic field is changed.

The study that detailed asymmetrical magnetic reconnection, used data from the four European Space Agency satellites in the Cluster mission - satellites which fly in formation in the earth's magnetic field.

"Especially important were measurements with two satellites only tens of kilometres from each other, in the region where the solar wind meets the earth's magnetic field," said Daniel Graham from Swedish Institute of Space Physics (IRF) in Uppsala in Sweden.

"We can thus carry out detailed measurements to understand plasma physics at an altitude of 60,000 km," Graham noted.

Heating of electrons parallel to the magnetic field in conjunction with magnetic reconnection was of special interest.

"We believe that this is an important piece of the puzzle for understanding how magnetic reconnection works, how charged particles are accelerated, and how particles from different regions can be mixed with each other," Graham noted.

"Our detailed measurements in the earth's magnetic field can be used to understand the physics even in fusion reactors on earth, and in far distant regions in space that we can't reach with satellites," the researchers said.

The study appeared in the journal Physical Review Letters.