Sun’s bumpy magnetic fields might explain why its atmosphere is so hot
A small sounding rocket that launched from White Sands Missile Range in New Mexico in 2019 is now helping us understand the different layers of the sun. Mapping the magnetic fields that control those layers may allow scientists to predict solar flares that can be dangerous to satellites and other technology on Earth.
What we think of as the surface of the sun is a layer called the photosphere, which has been studied in detail for decades. The layer of the sun’s atmosphere above the photosphere, the chromosphere, is transparent to the naked eye, which has made it much harder to study.
David McKenzie at NASA’s Marshall Space Flight Center in Alabama and his colleagues used the sounding rocket, called the Chromospheric Layer Spectropolarimeter-2 (CLASP-2), to measure the magnetic fields in the chromosphere in detail for the first time. This is important because the magnetic fields here are intimately tied to solar flares and the transfer of heat and energy in the sun.
Right now, solar flares are often impossible to predict. “I can point at an image of the sun and tell you which regions are a loaded gun and which are not, but I cannot tell you when that trigger is going to get pulled,” says McKenzie. The trigger, whatever it is, probably lies in the magnetic fields in the chromosphere, he says.
The researchers found that the boundaries between the layers of the sun are less smooth than we thought, with the magnetic field strength varying widely along the borders. McKenzie compares it to trying to discern the height of a field of grass: from far away, the surface of the field might seem obvious, but the closer you get, the more clear the variations in the heights of individual blades of grass become.
Understanding these structures could also help us figure out why the outermost part of the sun’s atmosphere, the corona, is hundreds of times hotter than the sun’s surface. “It has no right being that hot, and yet it is,” says McKenzie. “We’re fairly sure that it’s because of the magnetic fields, because we see the most heat in the places where there are the most magnetic fields, but we don’t really know how that happens.”
Journal reference: Science Advances, DOI: 10.1126/sciadv.abe8406
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