NASAs closest ever flight to the sun answers solar wind mystery

https://www.newscientist.com/article/2226005-nasas-closest-ever-flight-to-the-sun-answers-solar-wind-mystery/

Parker Solar Probe and sun

The Parker Solar Probe is studying the sun

NASA/John Hopkins APL/Steve Gribben

NASA’s Parker Solar Probe, which launched towards the sun in 2018, has sent back its first detailed measurements from closer to the star’s surface than we have ever ventured before.

We already knew that the solar wind, a flood of energetic particles constantly flowing away from the sun, speeds up as it leaves the sun’s outermost layer. New measurements from the probe showed that the wind is even faster than expected, and strange features spotted in the sun’s magnetic field might help explain why.

“There are all of these kinks and switchbacks propagating out from the sun, which is very surprising and unexpected,” says Parker Solar Probe team member Jasper Halekas at the University of Iowa. “We can’t see them from far away, but when we get close to the sun we just see zillions and zillions of these features.”

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These S-shaped kinks, and the hot plasma flowing along them, move far faster than anything in their surroundings. They carry significant energy, says Halekas, so they could be connected to the larger mysteries of how the solar wind is accelerated to high speeds and why the corona – the sun’s tenuous outer layer – is so anomalously hot.

While that probably has something to do with the fast solar wind, which blows away from the sun at up to 750 kilometres per second, the sun also has a slow wind, which travels at less than 500 kilometres per second. The fast solar wind emerges from the sun via “holes” in the corona where the sun’s magnetic field points straight outward, but we have never been able to quite nail down where the slow wind comes from.

Now new measurements have revealed that this slow wind also comes from a hole in the corona, similar to the fast wind. “Coronal holes are usually more toward the poles, but there’s one near the equator and slow solar wind appears to be coming from there,” says Gregory Howes, also a Parker Solar Probe team member at the University of Iowa.

The probe has already passed nearly twice as close to the sun as any other spacecraft has ever been, which allowed it to look at the star in ways that are impossible from further away. And the spacecraft is set to move in for an even better look. “As we get twice as close again, which we will, and even more than that, are things going to look even stranger and more unexpected? Nobody knows yet,” says Halekas. But it should help us solve some of the sun’s biggest mysteries.

Journal reference: Nature, DOI: 10.1038/s41586-019-1813-z, 10.1038/s41586-019-1818-7 

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