NASA's Interface Region Imaging Spectrograph
SOLAR SPOTTER: NASA’s IRIS in the clean room, preparing for launch.Image: LMSAL

Above the surface of the sun, plasma roiling in the star’s atmosphere does something that so far defies explanation, and seems to defy physics: It gets hotter as it moves farther out.

In the corona, the expansive outer layer of the solar atmosphere that extends millions of kilometers from the sun’s surface, temperatures reach millions of kelvins. The surface, by contrast, is a tepid 6,000 K (around 5,700 degrees Celsius). Although astronomers have developed a few possible explanations in recent years, no one can say precisely how or why the corona gets so hot. A new satellite will scrutinize the underlying regions of the sun’s atmosphere, giving physicists a chance to dig down like botanists studying a plant’s roots and uncover information that may help them solve the mystery.

The satellite—NASA’s Interface Region Imaging Spectrograph (IRIS), a new ultraviolet space telescope—will examine the chromosphere, a long-ignored layer of plasma beneath the corona, in unprecedented detail. “I wonder if maybe we were staring too hard at the corona to understand the corona,” says IRIS scientist Charles Kankelborg, a physicist at Montana State University. “It may be that by backing out we can get some vital clues to what’s happening.”

via Why Does the Sun’s Corona Get So Hot? NASA Launches Telescope to Find Out: Scientific American.