Ions heading to Earth can forecast magnetic environment behavior

An observation from ESAs (European Space Agency) cluster, has revealed that high-speed beams of electrically charged particles (ions) accelerating towards Earth can provide an understanding of magnetic environment behavior around our planet.

Paris, Dec 8 : An observation from ESA's (European Space Agency) cluster, has revealed that high-speed beams of electrically charged particles (ions) accelerating towards Earth can provide an understanding of magnetic environment behavior around our planet.

Different theories were proposed in the 80's and 90's to explain the presence of these ion beams, but only recently, data collected by cluster satellites helped scientists to discriminate between these theories.

The Earth's magnetic field, or magnetosphere, deflects most solar wind, which is a continuous flow of matter (plasma) continuously ejected by the Sun in all directions. However, there are two regions located around the magnetic poles, known as the Polar Cusps, where solar particles can precipitate along magnetic field lines towards Earth's magnetic poles. At each pole, a significant fraction of these particles bounce back along the magnetic field lines and populate the Plasma Mantle, a layer of plasma located on the night-side of Earth, inside the magnetosphere and along its boundary.

Under the action of electromagnetic forces, plasma contained in the mantle drifts equator-ward, along the tail axis. On September 1, 2003, the Cluster satellites were flying in close formation in the magnetotail when three out of the fours satellites simultaneously detected two distinct beams of protons streaming Earthward, along the magnetic field.

The beams were moving at very high speeds - 1000 and 2400 km/s, respectively - and were observed for a period of about three minutes. Due to the way the plasma is transported in the magneto-tail, the same source could not have been responsible for accelerating both beams. So, scientists concluded that there were at least two independent sources for these accelerated beams.

A theory regarding the acceleration of the ions towards Earth was proposed 14 years ago.

According to theory, when plasma drifts from the plasma mantle and reaches the current sheet, a region located along the magnetic equator, it can cross a few areas called 'resonant locations', where the charged particles acquire kinetic energy and get accelerated along the magnetic field. The further these resonant locations are, the more energy the ions acquire. Such accelerated ions are then beamed back to Earth, from the magnetic equator towards the poles, in a kind of elongated parabolic flight along terrestrial magnetic field lines.

More than 90 events of this kind (multiple accelerated ion beams) have been identified in the data recorded by Cluster from 2001 to 2003. They have been recorded during quiet or moderately disturbed geomagnetic periods, covering a large range of velocities.

Statistical studies based on Cluster measurements showed that the beams last about 10 to 15 minutes, and they extend between 1300 and 4500 km.

"Such results are possible only with missions like Cluster that, with multi-point observations lasting over several years, make it possible to accumulate a large amount of data and bridge observations with theory," said Philippe Escoubet, Project Scientist for Cluster and Double Star at ESA. "This is the only way to enhance our knowledge of the highly dynamic magneto-tail region," he added.

ANI