The Earth's Core Is as Hot as the Surface of the Sun

But the sun's surface isn't all that hot, at least compared with its atmosphere.

Wikimedia Commons

A new study in Science suggests that the temperature of our planet's core is much, much hotter than previously thought -- 6,000 degrees Kelvin, compared with earlier estimations that were closer to 5,000 degrees Kelvin. This temperature, blazing hot to a degree beyond comprehension, is the same as that of the surface of the sun. Yes, you read that right: the core of our temperate little atmospherically-protected home is as hot as *a star*.

Scientists in France were able to come to their remarkable conclusion in an experimental setting, using X-rays diffraction to watch how iron crystals held under unbelievable pressure form and melt. From their results, they extrapolated that the melting point of iron at 330 gigapascal -- thought to be the pressure* at the boundary of the inner core -- was 6230, plus or minus 500 degrees Kelvin, roughly similar to the sun's surface.

Now that is crazy, crazy hot. And there's no doubt that it is absolutely wild to imagine that deep beneath your feet is a center of molten iron as hot as a star. But before you get too bowled over -- our Earth has a star inside! -- there's something you should know: the surface of the sun is weirdly cool, at least when compared with the sun's atmosphere, known as the corona. There, the temperature reaches *1 to 2 million* degrees Kelvin. 6,000 degrees Kelvin suddenly seems practically balmy, doesn't it?

Solar_eclipse_1999_4_NR.jpgThe sun's corona, visible during an eclipse (Wikimedia Commons)

How is it that the sun's corona reaches such a high temperature, while its surface remains so much cooler?

The answer is ... we don't quite know. As Jay M. Pasachoff, an astronomer at Williams College, told Scientific American, the matter of why the sun's corona is so hot is "one of the important unsolved problems of astrophysics." Most of the going theories point to some phenomenon of the sun's magnetic field, but the exact mechanism by which the magnetic field draws heat to the region beyond the sun's surface is debated, with one recent paper pointing to "tornado-like swirls" as the culprit. With three new solar observatories planned for the years ahead, scientists hope to gain a better view of our star and get ever closer to their answer.

This word originally read as "temperature" when what I had intended was pressure. Thanks to Jason Quinley for pointing out the error.

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Rebecca J. Rosen is a senior editor at The Atlantic, where she oversees the Business Channel. She was previously an associate editor at The Wilson Quarterly.

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