ESA title
Magnetic reconnection observed by Cluster
Science & Exploration

Cluster opens a new window on ‘magnetic reconnection’ in the near-Earth space

12/03/2007 1497 views 0 likes
ESA / Science & Exploration / Space Science / Cluster

Plasma physicists have made an unprecedented measurement in their study of the Earth's magnetic field. Thanks to ESA's Cluster satellites they detected an electric field thought to be a key element in the process of 'magnetic reconnection'.

Thanks to these measurements, obtained by the eight PEACE electron sensors onboard the four spacecraft, scientists now have their first insight into magnetic reconnection's detailed behaviour.

Magnetic reconnection is a process that can occur almost anywhere that a magnetic field is found. In a reconnection event, the magnetic field lines are squeezed together somehow and spontaneously reconfigure themselves. This releases energy. When it occurs near the surface of the Sun, such an event powers giant solar flares that can release thousands of millions of tonnes of electrically charged particles into space.

The Earth's magnetic field creates a buffer zone, the magnetosphere, between our planet's atmosphere and the particles released during these eruptions. The Sun also releases a steadier flow of charged particles called the solar wind. On the large-scale, any heading this way buffet the magnetosphere, and are deflected by it. Plasma physicists describe this behaviour with a theory called 'magneto-hydrodynamics' (MHD).

The scales of magnetic reconnection
The scales of magnetic reconnection

On smaller scales, however, the picture becomes rather more complicated. The particles can actually flow across the magnetic field lines.This makes the mathematics of the behaviour more difficult. First to misbehave are the ions (positively charged particles). These break away from simple MHD on scales of less than a few hundred kilometres. On even smaller scales, less than 10 kilometres, the electrons (negatively charged particles) begin playing by other rules, too.

The new Cluster measurements reveal the electric field on the scale of a few hundred kilometres. "This is the first ever measurement of this term," says Paul Henderson, from University College London's Mullard Space Science Laboratory, UK, who led the investigation.

On 17 August 2003, Cluster was flying high above the night-time hemisphere of the Earth with an average separation of 200 kilometres between spacecraft. Data from several instruments shows that at 18:00 CET, a reconnection event took place and swept across the spacecraft.

Using data from Cluster's Plasma Electron and Current Experiment (PEACE) Henderson and collaborators calculated the pressure of electrons at each spacecraft and then calculated the difference between them and the variation with time. Using these quantities they calculated the electric field present near a reconnection site.

Cluster observes 'magnetic reconnection'
Cluster observes 'magnetic reconnection'

"This is an impossible calculation to make without four spacecraft," says Henderson. Now that the scientists can calculate the electric field in such a way, they have a new window into the process of magnetic reconnection.

Magnetic reconnection within Earth's magnetosphere regularly takes place on the night-time side of our planet, where the flow of the solar wind stretches out the magnetic field into a long tail. When the field reconnects in this region, it triggers jets of energetic particles that can cause auroral lights but can also damage satellites.

This new Cluster result takes scientists a step closer to seeing the precise details of magnetic reconnection. "When you think that the magnetosphere stretches over a million kilometres through space, we are actually looking at a minuscule part of it," says Henderson.

And that's exactly what plasma scientists want – the microphysics.

Note for editors

The original paper, "Cluster PEACE observations of electron pressure tensor divergence in the magnetotail," by P.D. Henderson at el., is published in Geophysical Research letters (Vol. 33, L22106, doi:10.1029/2006GL027868, 2006).

For more information

Paul Henderson, University College London's Mullard Space Science Laboratory, UK
Email: pdh @ mssl.ucl.ac.uk

Philippe Escoubet, ESA Cluster Project Scientist
Email: philippe.escoubet @ esa.int

Related Links

Science & Exploration

Double Star overview

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

Cluster overview

01/01/1970 25447 views
Open item
Auroral arcs
Science & Exploration

Cluster – new insights into the electric circuits of polar …

09/02/2007 2057 views 1 likes
Read
Double Star, an artist's impression
Science & Exploration

Double Star mission extended

16/11/2006 1089 views 2 likes
Read
Double Star Programme (DSP)
Science & Exploration

Double Star mission extension approved by ESA

12/05/2005 1029 views 0 likes
Read
Cluster and Double Star orbits on 8 May 2004
Science & Exploration

Details of solar particles penetrating the Earth’s environm…

03/10/2006 3855 views 2 likes
Read
Earth's magnetosphere- an artist's impression
Science & Exploration

Cluster makes an effervescent discovery

20/06/2006 1496 views 2 likes
Read
Artist's impression of the electrical and magnetic energy  event  of August 2004
Science & Exploration

Cluster and Double Star witness a new facet of Earth’s magn…

30/03/2006 1395 views 0 likes
Read
Artist's impression of cracks on a neutron star's surface
Science & Exploration

Cluster and Double Star see star crack during massive ‘star…

21/09/2005 2332 views 2 likes
Read
Double Star  'Tan Ce 2' satellite successfully launched
Science & Exploration

Second Double Star satellite successfully launched

26/07/2004 1014 views 0 likes
Read
Sun-Earth day events
Science & Exploration

How the Sun affects us on Earth

26/06/2003 36405 views 221 likes
Read
Cluster
Science & Exploration

Surfing and diving in the Earth's magnetosphere, Cluster ce…

17/07/2001 2270 views 0 likes
Read
The magnetosphere - a natural protective bubble
Science & Exploration

Cluster's new view of near-Earth space

16/02/2001 1975 views 1 likes
Read
On 4 November captured by SOHO/LASCO
Science & Exploration

Solar storm blasts Cluster

13/11/2001 1317 views 1 likes
Read
Large waves rock regions of the magnetosphere
Science & Exploration

ESA's Cluster sees 'squashed' magnetosphere

31/10/2003 1051 views 1 likes
Read