NASA’s Parker Solar Probe has ventured near enough to the Sun to reveal the source of fast solar wind. Such details about solar wind structure are lost when the wind exits the Sun’s corona as a gust of charged particles.
Parker has detected streams of high-energy particles that correlate to pockets on the Sun’s surface known as coronal holes.
These are areas where a magnetic field emanates outward into the space around the Sun without looping back into its surface. These holes tend to appear near the Sun’s poles, so the fast solar wind they generate doesn’t hit Earth.
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But, when the Sun gets active every 11 years due to the flipping of its magnetic field, these coronal holes appear all over its surface, with some of the fast solar wind they produce reaching Earth.
We’re just about to enter into exactly this kind of active period, known as a solar maximum. And this solar maximum is already shaping up to be a doozy, with reports in recent months suggesting the Sun is more active than it has been in decades. This spells danger for the technology on which we rely including GPS, telecommunications and other satellite-based tech which would be affected by severe solar winds.
Predicting solar storms is very difficult. Scientists hope that understanding their origin will make it easier to forecast their severity and frequency.
Despite seeing it every day, there’s a lot we don’t understand about our Sun. The Parker Solar Probe was launched in 2018 to help solve some of our central star’s mysteries by venturing closer to it than ever before. In 2021, became the first spacecraft to enter the Sun’s outer atmosphere.
Parker’s latest stream of data helps build a picture of how fast solar winds are produced. The results are published in Nature.
“Winds carry lots of information from the Sun to Earth, so understanding the mechanism behind the sun’s wind is important for practical reasons on Earth,” says co-author James Drake, a distinguished professor at the University of Maryland. “That’s going to affect our ability to understand how the Sun releases energy and drives geomagnetic storms, which are a threat to our communication networks.”
The team’s analysis suggests that coronal holes act like showerheads, with high-energy particles streaming out of roughly even spaced spots where magnetic fields funnel into and out of the Sun’s surface. When magnetic field lines cross, the fields break and reconnect, slinging charged particles into space.
“The photosphere is covered by convection cells, like in a boiling pot of water, and the larger scale convection flow is called supergranulation,” explains first author Stuart D. Bale, a professor of physics at the University of California, Berkeley. “Where these supergranulation cells meet and go downward, they drag the magnetic field in their path into this downward kind of funnel. The magnetic field becomes very intensified there because it’s just jammed. It’s kind of a scoop of magnetic field going down into a drain. And the spatial separation of those little drains, those funnels, is what we’re seeing now with solar probe data.”
By the time solar winds reach Earth, about 150 million kilometres from the Sun, they come in the form of a uniform, turbulent jet of swirling magnetic fields intertwined with charged particles.
Parker had to reach a distance from the surface of the Sun of only a little more than eight million kilometres to be able to discern the jets of material.
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