Satellites see largest jet of particles created between Sun andEarth (Forwarded)

ESA News
http://www.esa.int

11 January 2006

Satellites see largest jet of particles created between Sun and Earth

A flotilla of space-weather satellites -- ESA's Cluster and NASA's ACE and
Wind -- observed for the first time steady large-scale jets of charged
particles in the solar wind between the Sun and Earth.

When such huge jets of particles impact on Earth's magnetic shield, they
could cause powerful magnetic storms on our planet. Understanding the
mechanism behind these phenomena -- called 'magnetic reconnection' -- is
also fundamental to many explosive phenomena, such as solar flares,
powerful gamma-ray bursts from 'magnetars' (dead stars noted for their
extreme magnetic fields) and laboratory nuclear fusion.

Magnetic reconnection is a natural process by which the energy of magnetic
field is converted into particle energy and by which, for instance, solar
particles can penetrate through Earth's magnetic shield, sometimes causing
magnetic storms as well as beautiful 'aurorae', or polar lights.

Magnetic reconnection takes place when sheets of oppositely directed
magnetic field get pressed together. In doing so, the sheets cross to form
an X-shape that is then temporarily broken to form a new magnetic line
geometry.

The creation of a different geometry induces jets of electrically charged
particles and also allows solar material to pass through newly created
'cracks' in the previously impenetrable magnetic field configuration.

So far, magnetic reconnection events have been almost exclusively reported
in Earth's magnetosphere. This is the natural magnetic shield surrounding
Earth. It is composed of magnetic field lines generated by our planet, and
defends us from the continuous flow of charged particles that make up the
solar wind by deflecting them away from Earth.

However, when the interplanetary magnetic field lines carried by the solar
wind happen to be in the opposite orientation to Earth's magnetic field
lines, reconnection is triggered and solar material can break through
Earth's shield.

Previous reconnection events measured in Earth's magnetosphere suggested
that the phenomenon was intrinsically random and patchy in nature,
extending not more than a few tens thousand kilometres.

However, a broader picture of magnetic reconnection emerged when six
spacecraft -- the four Cluster and the ACE and Wind satellites -- were
flying in the solar wind outside Earth's magnetosphere, in sunward
direction, on 2 February 2002.

During a time span of about two and a half hours, all spacecraft observed
in sequence a single huge stream, or jet, of charged particles, up to 2.5
million kilometres (390 Earth radii) wide, caused by the largest
reconnection event ever measured.

"If the observed reconnection were patchy, one or more spacecraft most
likely would have not encountered an accelerated flow of particles," says
Tai Phan, from the University of California, Berkeley, USA, lead author of
the results.

"Furthermore, patchy and random reconnection events would have resulted in
different spacecraft detecting jets directed in different directions,
which was not the case."

The fact that the spacecraft detected the jet for more than two hours,
also implies that the reconnection must have been almost steady over at
least that timespan. Another 27 reconnection events of large magnitude --
with the associated jets -- were identified by ACE and Wind, four of which
extended more than 100 Earth radii, or 650 000 kilometres.

Thanks to these additional data, scientists could conclude that
reconnection in the solar wind is to be looked at as an extended and
steady phenomenon.

Magnetic reconnection, responsible for transport of mass and energy across
Earth's magnetic defences, is a central issue in space physics.
Consequences of this transport can be strong magnetic storms that have the
potential to severely impair critical technology infrastructure.

Potential damage includes widespread power failures, pipeline corrosion,
shutdown of cable systems, satellite failures, inaccurate GPS positioning
and disturbed radio navigation.

Understanding magnetic reconnection is also fundamental when having to
control magnetic fields and particles energy during nuclear experiments in
laboratories. One of the keys to producing 'clean' nuclear energy (nuclear
fusion) is making sure that reconnection phenomena do not take place, as
they could cause powerful and dangerous jets of particles to be released
uncontrolled.

"Only with co-ordinated measurements by spacecraft like Cluster, ACE and
Wind can we probe the near-Earth space environment with unprecedented
detail and in three dimensions," continued Phan.

"This is the only natural laboratory were the physics of plasma and the
magnetic phenomena that drive it can be studied in situ, paving the way to
many applications," he concluded.

Notes to editors:

The findings appear in the cover article of the 12 January 2006 issue of
the scientific journal Nature, titled: 'A magnetic reconnection X-line
extending more than 390 Earth radii in the solar wind'. The authors a
T.D. Phan, M.S. Davis, M. Oieroset, R.P. Lin (Univ. California, Berkeley,
USA), J.T. Gosling (Univ. Colorado, Boulder, USA), R.M. Skoug (Los Alamos
National Laboratory, New Mexico, USA), R.P. Lepping (NASA/GSFC, Maryland,
USA), D.J. McComas (South-west Research Institute, San Antonio, Texas,
USA), C.W. Smith (Univ. New Hampshire, USA), H. Reme (CESR, Toulouse,
France), A. Balogh (Imperial College, London, UK).

For more information:

Tai Phan, University of California, Berkeley, USA
E-mail: phan @ ssl.berkeley.edu

Philippe Escoubet, ESA Cluster Project Scientist
E-mail: philippe.escoubet @ esa.int

More about...

* Magnetic reconnection

http://clusterlaunch.esa.int/science...objectid=36452
* This story in depth
http://sci.esa.int/science-e/www/obj...objectid=38574
* Cluster factsheet
http://www.esa.int/esaSC/SEMYN5T1VED_index_0.html

Related articles

* Cluster helps to protect astronauts and satellites against 'killer
electrons'
http://www.esa.int/esaCP/SEMEHH8A9HE_index_0.html
* From 'macro' to 'micro' -- turbulence seen by Cluster
http://www.esa.int/esaCP/SEM18O808BE_index_0.html
* Cluster's new view of near-Earth space
http://www.esa.int/esaCP/ESA6VTTM5JC_index_0.html
* How the Sun affects us on Earth
http://www.esa.int/esaSC/SEML7BS1VED_foryou_0.html
* Space weather
http://www.esa.int/esaSC/SEMLC2T1VED_index_0.html
* What are solar flares?
http://www.esa.int/esaSC/SEMHKP7O0MD_index_0.html
* Click here for a video of a 'Solar tantrum'
http://esamultimedia.esa.int/video/s...r_tantrums.mpg

Related links

* ESA's Space Weather pages
http://www.esa.int/spaceweather

IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/esaCP/SEMAFQG23IE_index_1.html]
ESA Cluster and NASA Wind and ACE spacecraft encounters of solar particle
jets spanning 2.5 million kilometres in the solar wind. The particle jets
(indicated by red arrows) are sandwiched between sheets of opposite
magnetic fields.

Credits: Matt Davis, Univ. Calif. Berkeley

[Image 2:
http://www.esa.int/esaCP/SEMAFQG23IE...html#subhead2]
Artist's impression of the ESA Cluster mission, with four spacecraft
flying in formation above Earth.

Credits: ESA