Sun's Heat Takes Magnetic Carpet Ride

Hot loops. Sweeping magnetic field lines, thousands of kilometers long, rise above the sun's surface and heat its atmophere. Each loop carries as much energy as a large hydroelectric plant would generate in a million years.

As weird and illogical as a lake freezing over on a warm summer day, heat from the sun appears to flow from its surface--a mere 6000 degrees Celsius or so--toward the sizzling corona, which averages a few million degrees. Researchers have long suspected that this apparent paradox can be explained by ripples in the sun's magnetic field propelling the corona's energy outward, but they have had a hard time determining where the energy comes from in the first place. Now scientists may have found the source: At a NASA press conference today, researchers reported that a churning carpet of magnetic field loops, spotted by satellite, is strong enough to release more than enough energy to heat the corona A team led by Alan Title of the Stanford-Lockheed Institute for Space Research in Palo Alto, California, tracked, for the first time, the birth of small magnetic fields close to the sun's surface. Using data from the Doppler imager aboard the Solar and Heliospheric Observatory spacecraft (SOHO), which is drifting about 1.5 million kilometers sunward from Earth, the group made movies of magnetic field loops that seem to emerge from the center of convection cells on the sun's surface. Above these regions, which churn up hot gas from the interior, the loops would stretch and periodically break apart, releasing energy like a rapidly untangling rubber band. "The whole pattern would have changed after 40 hours," says Mandy Hagenaar, a solar physicist also at the Stanford-Lockheed Institute for Space Research. Computer models estimated that the magnetic fields could generate 10 times the amount of energy needed to cook the corona.

The group also linked the most vigorously writhing magnetic fields with particularly blistering regions in the corona detected with SOHO's ultraviolet telescope. But scientists still need to work out precisely how the magnetic energy gets transformed into heat. "We have a lot of circumstantial evidence," says George Withbroe, director of NASA's Sun-Earth Connection Program, "but we still don't know the exact details." With the wealth of data pouring in from SOHO, however, he says, "there is a good chance we'll have this nailed in the next few years."

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