New discovery on magnetic reconnection to impact future space missions(Forwarded)

ESA News
http://www.esa.int

23 January 2008

New discovery on magnetic reconnection to impact future space missions

ESA's Cluster mission has, for the first time, observed the extent of the
region that triggers magnetic reconnection, and it is much larger than
previously thought. This gives future space missions a much better chance
of studying it.

Space is filled with plasma (a gas composed of ions and electrons,
globally neutral) and is threaded by magnetic fields. These magnetic
fields store energy which can be released explosively, in a process called
magnetic reconnection.

This process plays a key role in numerous astrophysical phenomena: star
formation, solar flares and intense aurorae, to name a few. On Earth,
magnetic reconnection prevents the efficient production of electricity in
controlled fusion reactors, potential sources of electricity for the
future.

At the heart of magnetic reconnection is the 'electron diffusion region',
where reconnection is thought to be triggered. Here, a kink in
newly-reconnected magnetic field lines produces large-scale high-velocity
jets of plasma.

"Understanding the structure of the diffusion region and its role in
controlling the rate at which magnetic energy is converted into particle
energy remains a key scientific challenge," says Dr Michael Shay,
University of Delaware, USA.

Until recently, theoretical scientists believed that the electron
diffusion region was relatively tiny (width about 2 km, length about 10
km). In the vastness of space, the chance of a spacecraft encountering
this region would therefore be exceedingly small.

With increased computational power, simulations showed electron diffusion
regions that were a lot more elongated than those seen earlier. It was not
possible to judge whether the new finding was real because the length of
the region increased with more powerful simulations. Nor it was known
whether such a layer would be stable in the real, 3D world.

On 14 January 2003, the four Cluster satellites were crossing the
magnetosheath, a turbulent plasma region located just outside Earth's
magnetosphere, when they encountered an electron diffusion region. The
length of the observed region measured 3000 km, 300 times longer than the
earlier theoretical expectations and four times longer than seen in recent
simulations. Nevertheless, the observations strongly support new
simulations.

"These Cluster observations are very significant since they are the first
measurements of the length of the electron diffusion region in the space
environment. The finding drastically changes the way we understand the
physics of reconnection," noted Dr James Drake, University of Maryland,
USA.

"This discovery of a large electron diffusion region gives future ESA and
NASA missions a much better chance to study it," said Tai Phan at the
University of California at Berkeley, USA, lead author of the paper on the
findings.

Cluster was able to detect the region based on its high-resolution
magnetic field, electric field and ion measurements. But to understand the
fundamental physics of the electron diffusion region responsible for
reconnection, higher time resolution measurements are needed to resolve
the layer.

The four spacecraft of NASA's Magnetospheric Multi-Scale mission, planned
for launch in 2014, are being designed for such measurements. Cross-scale,
a mission under study at ESA in collaboration with other space agencies,
would use 12 spacecraft to probe the diffusion region, whilst
simultaneously measuring the consequences of energy released by
reconnection in the surrounding environment.

"With the higher probability of encountering the electron diffusion
region, we can be confident that future missions will be able to fully
understand magnetic reconnection," said Dr Philippe Escoubet, ESA's
Cluster and Double Star Project Scientist and Cross-scale Study Scientist.

Notes for editors:

The findings appear in, 'Evidence for an elongated ( 60 ion skin depths)
electron diffusion region during fast magnetic reconnection,' by T. Phan,
J. Drake, M. Shay, F. Mozer and J. Eastwood, published in the Physical
Review Letters, on 21 December 2007.

For more information:

Dr. Tai Phan, Space Sciences Laboratory, UC Berkeley, USA
Email: Phan @ ssl.berkeley.edu

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

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