Scientists Reveal How Our Sun Heats its Corona to Extreme Temperatures

A decades-long mystery has plagued the sun's corona. Scientists have long wondered how our nearest star manages to heat its corona to such extreme temperatures. Now, they may finally have their answer. They've found evidence that magnetic waves in a polar coronal hole contain enough energy to heat the corona and also deposit most of their energy at sufficiently low heights to cause the heat to spread throughout the corona.

So what exactly is the coronal heating problem?  Nuclear fusion in the center of the sun heats the solar core to 15 million degrees. Moving away from this furnace and by the time you arrive at the surface of the sun, this gas has cooled to a mere 6,000 degrees. That contrasts sharply with the temperature of the gas in the corona above the sun's surface, which soars back up to over one million degrees. What exactly causes this extreme temperature change has remained a source of speculation for decades.

That doesn't mean that there aren't theories. There are two dominant ones to explain this mystery. The first one attributes the heating to the loops of magnetic field which stretch across the solar surface and can snap and release energy. The second theory dictates that waves emanate from below the solar surface which then carry magnetic energy and deposit it in the corona. While both of these processes occur, the researchers have been unable to pinpoint which one is responsible for heating the corona.

In order to get a better look at the sun, the researchers analyzed data from the Extreme Ultraviolet Imaging Spectrometer onboard the Japanese satellite Hinode. More specifically, they examined a polar coronal hole, which is a region of the sun where the magnetic fields lines stretch from the solar surface far into interplanetary space.

In the end, the scientists saw that magnetic waves were the answer to this coronal heating mystery. The findings reveal a little bit more about how the Sun heats itself and opens up a realm of further questions. Currently, researchers plan to investigate what causes the waves to damp.

The findings are published in The Astrophysical Journal.