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Particle Physics and Astronomy Research Council
Swindon, U.K.

Contact Details:

Dr Louise Harra
Mullard Space Science Laboratory, UCL
Tel: 44 (0) 1483 204141
Fax: 44 (0) 1483 278312
Email: lkh{at}mssl.ucl.ac.uk

Alexi Glover
TOS-EMA
ESA/ESTEC
Keplerlaan, 1
Postbus 299
2200 AG, Noordwijk
Email: Alexi.Glover{at}esa.int

Julia Maddock
Press Officer, PPARC
Tel: 01793 442094
Email: julia.maddock{at}pparc.ac.uk

10 February 2003

Violent truth behind Suns Gentle Giants uncovered
=================================================
By Julia Maddock

Solar Physicists at the Mullard Space Science Laboratory, University 
College London (MSSL-UCL) have discovered new clues to understanding 
explosions on the Sun.

Coronal mass ejections are violent explosions that can fling 
electrified gas [plasma] with a mass greater than Mount Everest 
towards the Earth with destructive consequences for satellites. They 
can originate from active regions on the Sun, long known to consist of
forests of loops filled with plasma. These active loops are roughly 
50,000 km in size. However, active regions on either side of the solar 
disk are frequently connected by giant loops, which can bridge the 
Sun's equator. These loops have long been thought of as the gentle 
giants of the Sun, but in a paper to be published early this year in 
the journal of Astronomy and Astrophysics, the researchers describe 
the explosive characteristics of these giants.

An example of a giant loop can clearly be seen in the figure where the 
width of the arrow represents the size of the Earth. These giant loops 
of plasma are 450,000 km long -- large enough to engulf 40 Earths. If 
Concorde could fly along one of these loops, it would take nearly 9 
days to complete the journey!

Coronal mass ejections are violent explosions that cause all sorts of 
effects from the destruction of satellites, to the creation of the 
aurora. These effects are commonly referred to as 'space weather'. 
Using data taken by the Yohkoh and SOHO satellites studying the Sun, 
the scientists analysed the giant loops to see how frequently they 
erupt. In the past only one eruption had been observed and so they 
have been considered the gentle giants of the Sun that do not explode. 
The researchers found that not only can these huge structures be 
thrown away from the Sun, but they can also be heated up by a factor 
of 5, to temperatures of 14 thousand times the temperature of boiling 
water. They investigated how the loops explode, and it was found that 
the longer the loop, the more likely it is to erupt -- so these are 
culprits to watch more carefully in the future!

Alexi Glover, part of the space weather team at the European Space 
Agency [ESA], explains, "These huge loops have been observed for many 
years -- but their connection with coronal mass ejections is only just 
being understood.  In the future we hope to be able to predict coronal 
mass ejections before they take place, and step by step we are heading 
towards that goal."

Because of our increasing reliance on communication and navigation 
satellites for TV, GPS and national and international security, it is 
vital that we understand how the Sun can release these explosions.

Dr. Louise Harra of MSSL-UCL says, "Space weather is a rapidly 
developing field, and a vital key to progress is by understanding in 
detail the physics of Sun. The UK plays a leading role in solar 
physics and these new results are helping us make substantial 
advancements in our understanding of these beautiful, but potentially
hazardous, coronal mass ejections."

Notes for editors:

The Particle Physics and Astronomy Research Council (PPARC) is the 
UK's strategic science investment agency.  It funds research, 
education and public understanding in four areas of science -- 
particle physics, astronomy, cosmology and space science.

PPARC is government funded and provides research grants and 
studentships to scientists in British universities, gives researchers 
access to world-class facilities and funds the UK membership of 
international bodies such as the European Laboratory for Particle 
Physics (CERN), and the European Space Agency. It also contributes 
money for the UK telescopes overseas on La Palma, Hawaii, Australia
and in Chile, the UK Astronomy Technology Centre at the Royal 
Observatory, Edinburgh and the MERLIN/VLBI National Facility, which 
includes the Lovell Telescope at Jodrell Bank observatory.

PPARC's Public Understanding of Science and Technology Awards Scheme 
funds both small local projects and national initiatives aimed at 
improving public understanding of its areas of science.

IMAGE CAPTIONS:

[Figure 1:
http://www.pparc.ac.uk/Nw/Press/figure1_hres.jpg (278KB)]
Figure 1 shows the soft x-ray image of the loop. Image
taken by Yohkoh, a collaborative mission between Japan,
the United Kingdom and the USA. Copyright Yohkoh team.

[Figure 2:
http://www.pparc.ac.uk/Nw/Press/figure2_hres.jpg (423KB)]
Figure 2 shows the loop as it erupts into space as a coronal
mass ejection. Image taken by the SOHO satellite, a project
of international collaboration between ESA and NASA.
Copyright ESA/NASA.

[Figure 3:
http://www.pparc.ac.uk/Nw/Press/soho2_hres.jpg (182KB)]
Figure 3 shows an artist's impression of the SOHO craft
orbiting the Sun. Copyright ESA.

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