December 13, 2006. Copyright 2006, Graphic News. All rights reserved

NASA mission to see sun in 3D
By Mark Rutter

LONDON, December 13, Graphic News:  Although it may appear to us on Earth that the sun is an unchanging ball of fire, it is in fact in a state of constant flux. Periodically, violent solar storms are unleashed, during which enormous amounts of energy and strong magnetic fields are flung out into space. As these events can damage space satellites, and occasionally power networks on Earth, it would be useful if there was advance warning of when they are likely to occur. NASAÕs STEREO mission -- an acronym of Solar Terrestrial Relations Observatory -- is intended to make this possible.

Eight weeks after launch, the twin STEREO spacecraft are now in the first of four slingshot orbits, flying from a point close to Earth to one that extends just beyond the moon. 

The first lunar swingby is scheduled for Friday (December 15), when the Ahead (STEREO-A) spacecraft will use the moonÕs gravity to slingshot it into its operating orbit, drifting ahead of the Earth on an orbit slightly closer to the Sun than EarthÕs. Two weeks later the Behind (STEREO-B) spacecraft will take up position trailing the Earth on an orbit slightly further from Earth.

Because of these slight differences in the average distance from the Sun, the two spacecraft will slowly drift away from Earth in opposite directions. Their different orbits will give some depth perception -- or stereo vision -- allowing three-dimensional images of the sun and its storms to be created. As well as imaging telescopes, each probe will be equipped with instruments to track what happens to solar flares after they erupt by measuring particles and magnetic fields around them.

Also known as Òcoronal mass ejectionsÓ or CMEs, spontaneous solar storms or flares release gigantic amounts of energy without warning. These flares are generated as the equator and poles of the sun rotate at different speeds, twisting the starÕs magnetic fields into knots. This leads to a build up of magnetic forces or Òsun spotsÓ in some parts of the surface. After some time the pent-up energy erupts. High-energy particles, including X rays, radio waves and visible light, are ejected into space at millions of miles an hour, accompanied by a large, expanding magnetic field. It is possible for a billion tonnes of the sunÕs outer atmosphere to be blasted into space. Although the EarthÕs magnetic field protects it from the worst of these solar storms, satellites orbiting in space are particularly vulnerable, with possible disruption to telecommunications, mobile phone networks, and GPS signals.

There have been several incidences of considerable damage on Earth caused by solar storms. In 1859, a giant solar flare created a surge in magnetism that brought about powerful electrical currents in telegraph wires across Europe, with widespread fires breaking out as a consequence. The strongest solar storm in recent times occurred in 1989, resulting in damage to electricity cables and a blackout affecting six million people in Quebec.

Once the STEREO probes are operational it is hoped they will predict the strength and direction of solar storms about two and a half days before they occur. This will allow preventative action -- for example reducing the power to telecommunication satellites. Over the next five years the STEREO mission will monitor the increasing number of CMEs as the sun approaches a peak of its 11-year cycle of activity.
/ENDS