Saturday, November 10, 2012

Earth's magnetic shield behaves like a sieve

When the Earth's magnetic field and the interplanetary magnetic field are aligned, for example in a northward orientation as indicated by the white arrow in this figure, Kelvin–Helmholtz waves are generated at low (equatorial) latitudes. (Courtesy: ESA/AOES Medialab)

Earth's magnetic shield behaves like a sieve [excerpt]

The Earth's magnetic field is more permeable than previously thought, according to researchers analyzing data from the European Space Agency's Cluster mission. The findings have implications for modelling the dangers posed by space weather and could also help us better understand the magnetic environments around Jupiter and Saturn.

The solar wind is a stream of charged particles from the outer layers of the Sun blowing into the solar system. The Earth's magnetic field is thought to form a protective barrier against it.

It is well known, however, that if the magnetic field of the incoming solar wind has the opposite orientation to the Earth's magnetic field, then the field lines can break and join up again in a process known as "magnetic reconnection". This process allows the plasma from the solar wind to breach the boundary of the Earth's magnetic field – the magnetopause – where it can then potentially reach our planet.

This phenomenon was only thought to happen under special conditions, however. "We thought [it] was restricted to areas around the Earth's equator," Arnaud Masson, one of the scientists working on the Cluster mission, told Now, new analysis of Cluster data, initially obtained in 2003, shows the same thing happening at much higher latitudes, and at a wider range of magnetic-field alignments. "It seems that no matter what the orientation of magnetic fields, the same effect can occur," explains Masson. "It appears that it happens all the time, rather than just in special circumstances."