![]() A relatively narrow area called the transition region separates the corona from the chromosphere. The corona is above the Sun's lower atmosphere, which is called the chromosphere. The pressure and density in the corona is much, much lower than in Earth's atmosphere. The temperature in the corona is more than a million degrees, surprisingly much hotter than the temperature at the Sun's surface which is around 5,500° C (9,940° F or 5,780 kelvins). The material in the corona is an extremely hot but very tenuous plasma. ![]() It extends many thousands of kilometers (miles) above the visible " surface" of the Sun, gradually transforming into the solar wind that flows outward through our solar system. The corona is the outer atmosphere of the Sun. NCAR's High Altitude Observatory and NASA SDO< Even so, these new observations could help tease out how much of the heating comes from discrete heating events, helping researchers sort out a decades-old puzzle of great complexity.įor more news about big mysteries, stay tuned to views of the Sun's corona: during an eclipse (top) and in ultraviolet light (bottom). Testa emphasizes that other heating mechanisms may be at work, too. This is compatible with models from the University of Oslo, in which magnetic reconnection sets off heat bombs in the corona.” Paola Testa of the Harvard-Smithonian Center for Astrophysics, lead author of the paper reporting the results says, “Because IRIS can resolve the transition region ten times better than previous instruments, we were able to see hot material rushing up and down magnetic fields in the low corona. A recent observation by the observatory’s spectrographs has found evidence for these discrete, explosive events. Blink, and it looks much the same as uniform heating.įortunately, IRIS never blinks. If a heat bomb goes off, the resulting heat rapidly spreads out over a large region. The problem is the corona is a great thermal conductor. One of the big questions of coronal heating has been: Is the corona heated everywhere at once, or is heat delivered in discrete, bomb-like events?ĭe Pontieu says, “These two possibilities are very different, but the distinction can be difficult to observe.” These explosions happen when magnetic fields in the corona criss-cross and realign, exploding like a miniature solar flare. At the same time, “heat bombs” could be going off. For instance, plasma waves from the sun can rise into the corona and crash, depositing their energy there. Most researchers agree that the corona is probably heated in several different ways. “It can track the temperature and motions of hot gas at unprecedented spatial (0.33 arcsec), temporal (2 s) and spectral (2 mi/s) resolution.” “IRIS studies the transition region between the sun’s surface and the corona,” explains De Pontieu, who is the science lead of the observatory. On June 27, 2013, with campfires blazing around the USA, NASA launched the Interface Region Imaging Spectrograph (IRIS) - a space-based solar observatory designed to get to the bottom of how the solar atmosphere is heated. ![]() The problem involves a variety of complex physical processes that are difficult to directly measure or capture in theoretical models.” Solar physicist Bart De Pontieu of the Lockheed Martin Solar & Astrophysics Laboratory says, “The problem of coronal heating was first discovered in the 1940s. It is one of the most vexing problems in astrophysics. For more than a half-century, astronomers have tried to figure out what causes the corona to be so hot.
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