In May 2020, while still in its instrument-testing phase, the spacecraft swung halfway between the Sun and Earth. Solar Orbiter/EUI Team/ESA & NASA CSL IAS MPS PMOD/WRC ROB UCL/MSSLĮnter Solar Orbiter, which launched just over 1 year ago with six telescopic instruments and four sensors of its local environment. Solar Orbiter's Extreme Ultraviolet Imager found "campfires" (next to the white arrow), thought to be flares up to 4000 kilometers long. But until now, solar telescopes only had sharp enough vision to see the largest ones. Over the years, researchers have developed some "very slick ways of studying the very smallest flares" via their collective effects, says James Klimchuk of NASA's Goddard Space Flight Center. So they proposed that the corona is peppered with loops and flares with a wide range of sizes, most too small to see, that provide the missing heat through a wealth of smaller contributions. Researchers think these flares likely erupt when twisted, stress-filled magnetic loops snap and link up with other loops in a lower stress configuration, a process known as magnetic reconnection that releases huge amounts of energy.īut researchers realized in the 1960s that the loops and flares they could see did not provide enough heat to keep the corona cooking. Occasionally, active regions produce flares, eruptions of radiation and high-energy particles that sometimes reach Earth. Solar telescopes can see active regions in the corona where magnetic fields loop up from the surface, channeling superhot plasma up into the atmosphere and back down in arcs visible from Earth. The corona consists of plasma, a gas so hot that atoms fall apart, producing a roiling soup of ions and electrons buffeted by magnetic fields. "It's still one of the major unsolved problems in solar physics," says Sarah Matthews of University College London.Ī prime suspect is the Sun's turbulent magnetic field. They've puzzled over the mystery ever since. However, in the 1930s scientists discovered that the Sun's atmosphere, or corona, had a temperature of 1 million degrees Celsius, far hotter than the 5500☌ temperature of the surface. The Sun's heat comes from nuclear fusion in its core, and temperatures should decline moving outward. Other research at the meeting supports the long-held suspicion that small flares, not large ones, may do most of the heating. An analysis of observations made last year by the European-led Solar Orbiter mission, presented today at the European Geosciences Union (EGU) meeting, suggests tiny flares just above the Sun's surface, dubbed "campfires," could be enough to heat the atmosphere to its prodigious temperature. A new space mission is helping researchers solve one of the most enduring mysteries of our Sun: why its wispy atmosphere is nearly 200 times hotter than the surface below.
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