ESA title
Schematic of Earth’s night-side magnetosphere
Science & Exploration

High-speed beams of charged particles accelerate towards Earth

06/12/2007 4307 views 6 likes
ESA / Science & Exploration / Space Science / Cluster

ESA’s Cluster constellation has found that multiple, high-speed beams of electrically charged particles, or ions, are formed on the night-side of near-Earth space and get accelerated towards Earth.

These observations are key to understanding how solar material manages to reach the Earth’s night-side, to forecast the behaviour of the magnetic environment around our planet, and in turn, to better protect ground and space-based technologies.

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 the Cluster satellites helped scientists discriminate between these theories.

Earth’s magnetic field, or magnetosphere, deflects most solar wind - 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.

Creation of high-speed ion beams in near-Earth space
Creation of high-speed ion beams in near-Earth space

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 1 September 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 3 minutes.

Due to the way plasma is transported in the magnetotail, 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. 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.

Artist's impression of the four Cluster spacecraft
Artist's impression of the four Cluster spacecraft

A theory proposed about 14 years ago explains how this happens: when the plasma drifting from the plasma mantle reaches the current sheet, a region located along the magnetic equator, it can cross a few areas called ‘resonant locations’ (red rectangles in the animation), 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.

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,” says 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.”

Note for editors:

The results were obtained thanks to measurements of the Cluster Ion Spectrometry instrument onboard each satellite.

The results appear in two papers:
‘Spatial Temporal characteristics of ion beamlets in the plasma sheet boundary layer of magnetotail’, by E. Grigorenko et al, published in the Journal of Geophysical Research on 24 May 2007.

‘Multiplet structure of acceleration processes in the distant magnetotail’, by L. Zelenyi et al, published in the Geophysical Research Letters in 2006.

The theory, now confirmed by Cluster, was published in 1993 by M. Ashour-Abdalla et al., and predicted a universal scaling law for the velocity ratio of ion beams accelerated at distinct spatial sites in the magnetotail.

For more information:

Lev Zelenyi, IKI Space Research Institute, Russian Academy of Sciences, Moscow, Russia
Email: Lzelenyi @ iki.rssi.ru

Philippe Escoubet, ESA Cluster and Double Star Project Scientist
Email: Philippe.Escoubet @ esa.int

Related Links

Science & Exploration

Cluster overview

01/01/1970 25457 views
Open item
Science & Exploration

Double Star overview

01/01/1970 7980 views
Open item
Science & Exploration

SOHO overview

01/01/1970 58344 views
Open item
Science & Exploration

Solar Orbiter overview

01/01/1970 58172 views
Open item
Aurora borealis
Science & Exploration

Space weather

6485 views 27 likes
Read
Cluster observing the electron diffusion region
Science & Exploration

New discovery on magnetic reconnection to impact future spa…

23/01/2008 2309 views 1 likes
Read
Schematic of Earth’s night-side magnetosphere
Science & Exploration

High-speed beams of charged particles accelerate towards Ea…

06/12/2007 4307 views 6 likes
Read
CME observed by SOHO
Science & Exploration

Solar outburst pulls a magnetic slingshot

21/11/2007 1720 views 1 likes
Read
Artist's impression of the four Cluster spacecraft
Science & Exploration

Cluster monitors convection cells over the polar caps

22/10/2007 1583 views 0 likes
Read
Cluster and other spacecraft
Science & Exploration

Cluster and Double Star uncover more on bright aurorae

10/09/2007 1243 views 0 likes
Read
The Sun-Earth connection
Science & Exploration

Killer electrons in space are now less mysterious

26/07/2007 2242 views 0 likes
Read
Cluster II
Science & Exploration

Pioneering 3D view of near-Earth magnetic 'dance'

29/06/2007 1521 views 1 likes
Read
Cluster II
Science & Exploration

Cluster: ESA spacecraft flying closer than ever for better …

21/06/2007 1324 views 0 likes
Read
Aurora before and during a substorm
Science & Exploration

Cluster sees tsunamis in space

12/04/2007 1182 views 0 likes
Read
Solar ‘magnetic carpet’
Science & Exploration

Magnetic fields get reconnected in turbulent plasma too, Cl…

27/03/2007 2111 views 1 likes
Read
Magnetic reconnection observed by Cluster
Science & Exploration

Cluster opens a new window on ‘magnetic reconnection’ in th…

12/03/2007 1497 views 0 likes
Read
THEMIS joins the spacefleet of Sun-Earth connection explorers
Science & Exploration

NASA THEMIS mission adds five spacecraft to the Sun-Earth f…

16/02/2007 2627 views 2 likes
Read