Or magnetic waves rolling from deep within the sun could transfer energy and heat into the chromosphere and corona. One idea holds that magnetic field lines twist and braid as they skitter around the sun, building up tension and unleashing massive amounts of energy when they finally break like rubber bands. IRIS will test the two leading hypotheses that seek to explain the corona’s extreme heat. Magnetic fields do not naturally heat particles, Kankelborg notes: “If you take a magnet and suspend it on your refrigerator, the sausages don’t spoil.” Even so, astronomers are not sure how the sun’s magnetic fields drive these massive energy transfers. These jets may inject energy that keeps the corona at a rolling boil. These jets, called “type 2 spicules,” climb as high as Earth is wide but last only 100 seconds or so.

IRIS’s detailed readings will also help physicists track small-scale solar phenomena, such as the fleeting, thin fountains of hot plasma first discovered by de Pontieu and his colleagues in 2007. By figuring what’s going in and out, you can figure out what’s going on up there.” De Pontieu compares the mission with studying the air just above the ocean, watching as water evaporates and condenses: “You’re seeing the process that feeds the clouds, and the process that depletes the clouds. The IRIS team will use information from other satellites that observe the whole sun, such as Japan’s Hinode and NASA’s Solar Dynamics Observatory, to identify active areas of the sun and point IRIS toward flares as they grow, when it will obtain spectra every two seconds. And they should see plenty: IRIS will launch near the peak of the sun’s 11-year activity cycle. Physicists are also eager to observe solar outbursts with IRIS. “With these models we have now a fighting chance of understanding the light that we see coming from the chromosphere,” de Pontieu says. That is a key reason why IRIS’s time is now. Only in the last 10 years have physicists developed computer models sophisticated enough to track the photons coming from this region and to sufficiently simulate chromospheric activity. It absorbs and reemits some light from the surface, but it also emits its own UV light, making it difficult to identify where the photons originated, says Bart de Pontieu, the science lead for IRIS at the Lockheed Martin Solar and Astrophysics Laboratory in Palo Alto, Calif. Unlike the corona’s wispy prominences or the spotted, fiery surface, the chromosphere is tricky to behold. “You won’t just see beautiful images with fine-scale structure, but you’ll also be able to measure what the temperature is and what the density is,” says Eric Priest, a solar physicist at the University of Saint Andrews in Scotland who is not part of the IRIS team. Other telescopes, such as the Sunrise 2 balloon that recently completed a five-day flight around the Arctic circle, have looked at the chromosphere but haven’t returned such detailed information. IRIS will not only photograph the sun but will also return spectra-detailed breakdowns of the star’s light that can reveal subtle physical processes at work. From that vantage point the telescope will observe a small section of the chromosphere, a violently variable region between the corona and the surface. “It may be that by backing out we can get some vital clues to what’s happening.”Ī carrier aircraft will carry IRIS and a Pegasus rocket booster aloft from Vandenberg Air Force Base in California on June 26, and then launch it from there into a polar orbit. “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. 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. 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. Although astronomers have developed a few possible explanations in recent years, no one can say precisely how or why the corona gets so hot.

The surface, by contrast, is a tepid 6,000 K (around 5,700 degrees Celsius). 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. 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.

Sun corona helium