Published online 22 March 2007 | Nature | doi:10.1038/news070319-11

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X-ray snaps of the Sun yield surprises

Stunning video of collapsing magnetic arc baffles scientists.

Click here to watch a video.Click here to watch a video.NASA

The best images of the Sun yet obtained are now streaming in — and are proving both illuminating and baffling for scientists.

The Hinode spacecraft, an international mission led by the Japanese space agency JAXA, was launched in September 2006, and is now circling Earth in an orbit that gives it a good view of the Sun. The latest data to be sent back from its three main instruments are showing our star in all its glory as a dynamic, turbulent, mysterious hothouse of magnetic activity (see video).

Researchers have long been puzzled by the observation that the Sun's corona — the atmosphere of gas extending out from the Sun at a temperature of millions of degrees Celsius — is about a hundred times hotter than the Sun's surface. One possible explanation is that magnetic fields projecting from the Sun twist about in the turbulent environment until they eventually snap, releasing energy as heat. The data being returned by Hinode's X-Ray Telescope add weight to this theory.

"We can see the corona structures twisting and shearing," says Leon Golub of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. "There are things that look exactly as predicted," he says.

But some of the observations are proving more confusing. Astrophysicists have been stunned by a video image of a magnetic arc collapsing in on itself. "We are used to seeing magnetic fields emerging outwards," says Golub. But this one went in the other direction. "Nobody can explain how this happens," Golub says.

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Golub expects that this too may be related to the corona's high temperature, but as yet there is no theory to predict this kind of activity, he says.

"Processes that we see on the Sun are not intuitive and not easily explained," says Alan Title of the Lockheed Martin Advanced Technology Center in Palo Alto, California. Title works on Hinode's third instrument, the Solar Optical Telescope.

And it is likely to provide yet more surprises. "Almost every day we see data coming down and we don't know what they mean," says Golub.

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