The Sun’s X-file under the Spotlight

One of the Sun’s greatest mysteries is about to be unravelled by UK
solar astrophysicists hosting a major international workshop at the
University of St Andrews from September 6-9th 2004. For years scientists
have been baffled by the ‘coronal heating problem’: why it is that
the light surface of the Sun (and all other solar-like stars) has a
temperature of about 6000 degrees Celsius, yet the corona (the crown of
light we see around the moon at a total eclipse) is at a temperature of
two million degrees?

Understanding our nearest star is important because its behaviour has
such an immense impact on our planet. This star provides all the light,
heat and energy required for life on Earth and yet there is still much
about the Sun that is shrouded in mystery.

“The problem is like an Astrophysics X-file! It is totally counter
intuitive that the Sun’s temperature should rise as you move away from
the hot surface,” explains Dr Robert Walsh of the University of Central
Lancashire and co-organiser of the workshop. “It is like walking away
from a fire and suddenly hitting a hotspot, thousands of times hotter
than the fire itself.”

Using the joint ESA/NASA satellite, the Solar and Heliospheric
Observatory (SOHO), along with another NASA mission called TRACE,
researchers have gathered enough data to form two rival theories to
explain what has been termed ‘coronal heating’. It is now believed
that the Sun’s strong magnetic field is the culprit behind this unique
phenomenon. At this SOHO workshop, scientists from the UK and around the
world will look at the evidence for these two explanations and try to
untangle the clues we now have available to us.

Walsh continues, “SOHO’s contribution to the research has been so
important because for the first time we can take simultaneous magnetic
and extreme ultraviolet images of the Sun’s atmosphere, allowing us to
study the changes in the magnetic field at the same time as the
corresponding effect in the corona. Then, using sophisticated computer
simulations, we have constructed 3d models of the coronal magnetic field
that can be compared with SOHO’s observations.”

One possible mechanism for coronal heating is called ‘wave
heating’. Prof Alan Hood from the Solar and Magnetospheric Theory
Group at St. Andrews explains: “The Sun has a very strong magnetic
field which can carry waves upwards from the bubbling solar surface.
Then these waves dump their energy in the corona, like ordinary ocean
waves crashing on a beach. The energy of the wave has to go somewhere
and in the corona it heats the electrified gases to incredible
temperatures.”

The other rival mechanism is dependent on twisting the Sun’s magnetic
field beyond breaking point. Prof Richard Harrison of the UK’s
Rutherford Appleton Laboratory says “The Sun’s magnetic field has
loops, known to be involved in the processes of sun spots and solar
flares. These loops reach out into the Sun’s corona and can become
twisted. Like a rubber band, they can become so twisted that eventually
they snap. When that happens, they release their energy explosively,
heating the coronal gases very rapidly”.

The Sun is the only star astronomers can study in close detail and many
questions remain. The workshop will also look forwards to future
missions such as Solar-B, STEREO and Solar Orbiter that all have
important UK involvement through PPARC.

Notes for Editors

Relevant WWW sites

SOHO15 : Coronal Heating Workshop

http://www.soho15.org

Solar and Heliospheric Observatory

http://sohowww.nascom.nasa.gov

TRACE

http://vestige.lmsal.com/TRACE

Solar and Magnetospheric Theory Group, St. Andrews

http://www-solar.mcs.st-and.ac.uk

Website of relevant high resolution images

http://www.pparc.ac.uk/Nw/Md/Artcl/soho15_images.asp

Points of Contact

Julia Maddock,

Community Press Officer

Particle Physics & Astronomy Research Council

Tel +44 (0)1793 442094, Mobile 07901 514975

Fax +44 (0)1793 442002

Email: julia.maddock@pparc.ac.uk

Dr Robert Walsh (Co-organiser of SOHO15)

Centre for Astrophysics,

University of Central Lancashire

Phone: 01772-893557 or 07795 566591

E-mail: rwwalsh@uclan.ac.uk

Special expertise: the Sun; Coronal Heating; Magnetic Loops; SOHO,
TRACE, Solar-B

Dr. Jack Ireland (Co-organiser of SOHO15)

NASA Goddard Space Flight Center,

Greenbelt MD, USA

Phone: 01334 463753 (while in the UK) or 07821 610 163

E-mail: ireland@cdso8.nascom.nasa.gov

Special expertise: the Sun; Coronal Heating; Waves; SOHO, TRACE,
STEREO

Prof. Alan Hood,

Solar and Magnetospheric Theory Group,

University of St. Andrews

Phone: 01334 463710

E-mail: alan@mcs.st-and.ac.uk

Special expertise: the Sun; computer simulations of the solar
atmosphere

Prof. Richard Harrison,

Head of Space Physics Division

Rutherford Appleton Laboratory

Email R.A.Harrison@rl.ac.uk

Tel: (44) 1235 44 6884

Special expertise: the Sun, fundamental processes in the Sun’s
atmosphere, solar mass ejection, development and operation of
spectroscopic and imaging space instrumentation (SOHO, TRACE, STEREO,
Solar-B)

University of Central Lancashire – Media and Public Relations Office
Chris Theobald

Phone: 01772 894424/5

E-mail: ctheobald@uclan.ac.uk

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.