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Article 2006

From The Times of London, July 18, 2006

3-D views of Sun will allow forecast of "space weather"

By Mark Henderson, Science Editor
July 18, 2006

THE first three-dimensional views of the Sun will be captured by a pair of spacecraft to be launched next month, allowing scientists to forecast violent "space weather" that can knock out satellites and power grids.

Images from Nasa’s Stereo mission will transform the ability of astronomers to predict when the Sun is about to hurl an explosive spurt of superheated plasma towards Earth, where it can cause electronic havoc. These sudden bursts of solar activity, known as coronal mass ejections (CMEs), can release 100 times as much energy as the world’s entire nuclear arsenal.

On arrival the stream of charged particles can disable communications and navigational satellites, and even slip through the Earth’s protective magnetic field to interfere with electricity systems and mobile phone networks.

The bursts also cause the Aurora Borealis and Aurora Australis, the Northern and Southern Lights.

In 1989 a solar storm of this sort left six million people without power in Quebec, and in 2003 a similar event caused power cuts in Sweden and damaged several satellites and spacecraft, including the Mars Express probe then travelling to the Red Planet.

Although CMEs take about 2½ days to reach Earth, at present they can be detected only if they are aimed away from the planet. As terrestrial and orbiting telescopes look at the Sun head on, they are effectively blinded by its brightness behind the approaching cloud of plasma.

When Stereo becomes operational this year, scientists will be able finally to detect Earth-bound CMEs as soon as they leave the Sun’s surface, giving crucial time to prepare. Satellites can be turned around so their shielding faces the eruption, or switched to a lower voltage that leaves them at less risk, and power can be rerouted from threatened parts of electricity grids.

The mission works by viewing the Sun in three dimensions instead of two. A pair of probes will leave the Earth in opposite directions and monitor the Sun from different angles, providing binocular vision that makes CMEs much easier to see.

"With two spacecraft we will be much more able to predict the speed and direction of CMEs and provide a much earlier warning when CMEs are heading towards our planet," said Chris Davis, of the Rutherford Appleton Laboratory in Oxfordshire, a member of the Stereo team.

Professor Richard Harrison, also of the laboratory, said: "At the moment we only see the Sun from the viewpoint of the Earth. Removing that restriction will allow us to understand the Sun and, therefore, other stars as well, in a much better way. If you only saw a car from the front, you’d have no idea what it really looks like."

The British scientists have designed and built one of the most important instruments aboard the Stereo probes, the heliosolar imagers that will watch the Sun.

The two spacecraft will be launched on the same rocket from Cape Canaveral, Florida, between August 20 and September 6, and should start their observations in November.

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