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New Picture of Gravity Defying Loops on Sun
By Robert Roy Britt
Senior Science Writer
posted: 07:00 am ET
22 May 2002
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this is the first time we have had velocity measurements Gobs of hot material looping out from the Sun seem to mysteriously defy gravity, and some new measurements may provide insight into what's going on. The so-called coronal loops are attached to the Sun's surface at two points thousands of miles apart and loop out into space along strong magnetic field lines. If gravity were doing its job, the density of hot gas should be greater close to the Sun's surface compared with the outermost reaches of a loop, called the apex. "However, the density at the apex of the loop is up to three orders of magnitude larger than predicted," says Amy Winebarger of the Harvard-Smithsonian Center for Astrophysics. Several research teams have tried to explain the phenomenon, but not everyone agrees what's going on. Winebarger figured conditions at these two locations might be wildly different, stimulating a flow of material through the loops from a hot spot to a cooler region. Using NASA's Transition Region and Coronal Explorer (TRACE) spacecraft, Winebarger and her colleagues did in fact spot blobs of material flowing along the coronal loops. They searched for matching archived data from the SOHO spacecraft to determine the speed of the globs, which turned out to be about 67,000 mph (30 kilometers per second). "This is the first time we have had velocity measurements along the loops observed in TRACE and it was a surprise to see such large velocities," Winebarger told SPACE.com. She said the changing densities may be related to how the Sun's atmosphere, called the corona, is heated -- a process that is itself a mystery. The corona is much hotter than lower regions. Her team now believes that figuring out one mystery will solve the other. Understanding the corona is important also because it is where space storms originate, sending extra doses of charged particles toward Earth and sometimes disrupting communication systems.The results were detailed in a recent issue of the Astrophysical Journal. More Sun News | Astronomy News Briefs
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