Scientists have taken the highest resolution images of the sun’s atmosphere ever, and it offers an explanation for the decades-old mystery of why its outer most layer is up to 800 times hotter than its surface.
Using photos from the High Resolution Coronal Imager (Hi-C) that was flung into space in July, scientists observed small bands of magnetism near the star’s surface twist, turn and braid together before snapping apart, releasing heat and energy flares that heated up the star’s atmosphere. NASA officials described their findings Wednesday.
The sun’s surface is a relatively cool 5,000 degrees Fahrenheit while its atmosphere, or corona, is between 2 million and 4 million degrees. The disparity has long puzzled scientists who study our nearest star.
With a $5-million budget, scientists designed, built and launched a 464-pound, 10-foot telescope into space from White Sands, N.M., in July. The telescope was outside of the atmosphere for only five minutes before it returned to Earth. But in those few minutes, the telescope took high-resolution images of the corona, revealing what the sun’s magnetic fields were doing on a local scale. NASA scientists likened that to taking a high-resolution photo of a dime from 10 miles away.
The images showed how the relatively small magnetic fields braid together into unbearable tension, then snap apart in flares that can be as hot as 7 million degrees. The images supported a theory first introduced in 1983 by American astrophysicist Eugene Parker that small solar flares were heating up the sun’s outer most layer.
“Sometimes this small-scale process stalls, extra stress builds up, and then the relaxation happens on a much larger scale, causing a flare or coronal mass ejection,” said Karel Schrijver, who worked on the mission and is a senior fellow at Lockheed Martin Advanced Technology Center in Palo Alto.
A coronal mass ejection is a violent, massive burst of gas and magnetic fields from the sun. When the explosions are aimed toward Earth, they have been known to knock out power grids and damage satellites. But they can also bring on some pretty sweet northern lights, or Aurora Borealis.
“The flaring on the small scales and on the large scales all happen together,” Schrijver said. “To understand why the solar corona behaves as it does, we need to see both the small and the large to understand how they connect, and ultimately drive space weather.”
Hi-C is part of NASA’s Low Cost Access to Space Program, which uses smaller-scale missions for science investigations, to test future technologies and train upcoming researchers students and engineers. The photos were shot near the peak of the sun’s 11-year cycle, offering scientists their best shot at photographing its smallest flares, researchers said.
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