The Sun's X-file under the Spotlight

Sep 03, 2004

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.

Source: The Particle Physics and Astronomy Research Council

Explore further: SpaceX ship leaves ISS for Earth loaded with lab results

add to favorites email to friend print save as pdf

Related Stories

Beastly sunspot amazes, heightens eclipse excitement

22 hours ago

That's one big, black blemish on the Sun today! Rarely have we been witness to such an enormous sunspot. Lifting the #14 welder's glass to my eyes this morning I about jumped back and bumped into the garage.

'Twisted rope' clue to dangerous solar storms

Oct 22, 2014

A "twisted rope" of magnetically-charged energy precedes solar storms that have the potential to damage satellites and electricity grids, French scientists said on Wednesday.

New radio telescope ready to probe

Oct 21, 2014

Whirring back and forth on a turning turret, the white, 40-foot dish evokes the aura of movies such as "Golden Eye" or "Contact," but the University of Arizona team of scientists and engineers that commissioned ...

Cosmic rays threaten future deep-space astronaut missions

Oct 21, 2014

Crewed missions to Mars remain an essential goal for NASA, but scientists are only now beginning to understand and characterize the radiation hazards that could make such ventures risky, concludes a new paper ...

Cassini caught in Hyperion's particle beam

Oct 17, 2014

Static electricity is known to play an important role on Earth's airless, dusty moon, but evidence of static charge building up on other objects in the solar system has been elusive until now. A new analysis ...

Recommended for you

Hinode satellite captures X-ray footage of solar eclipse

Oct 24, 2014

The moon passed between the Earth and the sun on Thursday, Oct. 23. While avid stargazers in North America looked up to watch the spectacle, the best vantage point was several hundred miles above the North ...

User comments : 0