The blazing surface of the sun froths with an extremely hot electrically charged gas called plasma. The temperature at the edge of this cosmic furnace runs at about 5,500 degrees Celsius, but here’s the real puzzle: Somehow the sun’s atmosphere, which surrounds that surface like a halo, is 150 times hotter.
“Why is the corona 1 million degrees while the photosphere is at 5,500?” asks Yannis Zouganelis, deputy project scientist for the European Space Agency’s Solar Orbiter probe. “The main problem is, we have many ideas, many theories, but we have no real measurements.”
Until now. Last year, the Solar Orbiter swooped in for a close-up. It examined the corona from
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