June 16, 1998 BOZEMAN, MT--Scientists long perplexed over why the sun's corona is so hot now have a new clue about the actual heating mechanism that pushes temperatures in the sun's outer region into the millions of degrees.
Montana State University-Bozeman researcher Loren Acton, Eric Priest of St. Andrews University in Scotland and a team of European scientists have discovered that a clash of magnetic fields is likely to cause the heating of gigantic and super-hot loops of material that arch high above the sun's surface.
Their findings are reported in the June 11 issue of the journal Nature.
Published in England, Nature is an international weekly journal of science whose articles are intended for a broad scientific audience. For decades, scientists have known that the surface of the sun is about 6,000 degrees Celsius while the corona soars to several million degrees.
"The outer part of this atmosphere forms a giant halo of eerie light around the sun during a solar eclipse and consists of giant, super-hot loops that extend high above the sun's surface," Priest wrote in a press release from St. Andrews University.
Using the Soft X-ray Telescope aboard the Japanese/US/UK space satellite called Yohkoh, which means "sunbeam," the research team led by Priest has for the first time measured how the temperature varies along the giant loops.
Physicists had three interpretations of how the corona is heated. Some thought that heat is likely to be dumped at the feet of the loop and then conducted, like the flow of heat along a red-hot poker, to the rest of the loop. Others believed the heat should be deposited at the summit of the loop, while a third group predicted a uniform release of heat along loop, said Acton.
"Our data indicate that the heating must be uniform," he said.
The most likely mechanism is a clash of magnetic field lines, according to Priest.
"They tangle like spaghetti in the solar atmosphere and break, causing dozens of explosions that release energy along the loop," he wrote in the press release.
Acton said the finding "in no way" solves the puzzle of the corona's intense heat, but it does point the scientists toward the correct heating mechanism.
"It's a step in understanding the heating of the corona in general, but it's a far cry from reproducing in the computer what nature does," he said. Although it appears constant from the earth, the sun is a bubbling cauldron of energy now more visible to Acton and other scientists thanks to a variety of satellites that orbit outside the distortion of the earth's atmosphere.
Images can be found at http://www-solar.dcs.standrews.ac.uk/~eric/nature.html.
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