A Solar Mystery

The Sun’s Mysteriously Hot Atmosphere

image of sun with hazy corona around it.

The sun is surrounded by a hazy layer of gas called the corona. It's the sun's atmosphere. Credit: NASA/ESA/SOHO.

There are many ways in which the sun is different than Earth. For one thing, the sun is a broiling mass of superheated gas. Earth is a cool, wet planet where life flourishes. But there are some similarities. For one, both the sun and Earth have an atmosphere.

On Earth, the atmosphere is a layer of gas surrounding its surface. It contains, among other things, the oxygen we breathe. On the sun, it is a wispy layer of hydrogen gas much less dense than the gas that makes up the sun’s bright surface.

But contained within this solar atmosphere lies one of the great mysteries in science. The largest part of the sun’s atmosphere is a layer called the corona. For some reason the corona is hotter than the actual surface of the sun below it. Much hotter.

Why is the Corona So Hot?

The surface of the sun is almost 10,000 degrees Fahrenheit. That’s really hot. But the sun’s corona is over 200 times hotter—millions of degrees Fahrenheit. That’s like the actual flame of a fire being 200 times colder than the air around that fire.

cartoon of a cold sun surrounded by a hot corona indicating different temperatures at different levels.

The surface of the sun is cold compared to the super hot gas that makes up its atmosphere. And it gets hotter the further away you go! Nobody is quite sure why this happens.

Why would the area around a hot burning mass be hotter than something that is actually closer to the source of heat? And if the corona is so hot, then why doesn’t it heat up the sun’s surface to a similar temperature?

Well, the truth is that nobody knows for sure. Lots of scientists are hard at work trying to figure out the answer. One potential explanation is magnetic forces. All that superheated gas in the sun core creates a strong magnetic field—like Earth’s magnetic field, but a whole lot stronger and more chaotic. Some scientists think that it is this magnetic field that gives the sun’s corona energy.

Are Strong Magnetic Forces to Blame?

drawing of a sun's magnetic field with moving particles around them and a magnet over the sun.

Some scientists think that strong magnetic waves from deep within the suns interior make the atoms in the gas around the sun move very fast. The faster the atoms move, the hotter the gas.

If that were true, then powerful magnetic waves would be causing atoms in the gas surrounding the sun to move very quickly. The faster the atoms in something move, the hotter it is. That’s all heat is—moving atoms.

It’s very hard to study the sun, and scientists are still not entirely sure how magnetic force could produce heat, or why the surface of the sun is not heated by the hot corona. But that’s the great thing about science—there’s always some big mystery just waiting to be solved.

article last updated October 21, 2014
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