The sun’s surface is hot, sure — almost 10,000 degrees Fahrenheit — but the solar atmosphere, or corona, is somehow 4 million degrees. What gives? In April, scientists announced the main reason: small bursts of magnetic energy called nanoflares, which temporarily heat pockets of gas to 20 million degrees.
“The sun’s surface is much like a pot of hot oil on the stove,” says NASA solar scientist James Klimchuk. “Hot oil rises, spreads out horizontally, cools and falls back down to the bottom of the pot, only to rise again.” That constant movement can twist and tangle the magnetic fields that thread through the sun and extend into the corona. Eventually, like a rubber band, they reach a point where they snap. Scientists had theorized this would cause a nanoflare.
The tiny bursts, each releasing just one-billionth the energy of a normal flare, proved elusive. But in December 2013, during its 15-minute rocket flight, the Extreme Ultraviolet Normal Incidence Spectrograph spied solar material measuring 20 million degrees, matching nanoflare predictions.
“[These observations] confirm that nanoflares exist and heat at least some of the corona,” says Klimchuk. Next up is confirming nanoflares’ magnetic births and determining how often they occur.