The high-speed particles spew out of the sun like water from a shower head, scientists reported Wednesday.
Data from the Parker Space Probe, a NASA spacecraft that launched in 2018 and is now swooping down to collect readings of the sun’s outer atmosphere, or corona, is providing clues about how the sun generates the solar wind at a million of miles per hour flow of electrons, protons and other charged particles hurtling outward into the solar system.
The solar wind research ties into a mystery that has long puzzled scientists: Why is the corona, where temperatures soar into millions of degrees, so much hotter than the sun’s surface, which is a relatively cold 10,000 degrees Fahrenheit?
Parker spacecraft is named after Eugene N. Parker, a University of Chicago astrophysicist who first predicted the existence of the solar wind in 1958.
The sun has an atmosphere of soft gases that is pulled down by gravity as the pressure generated by fusion reactions within the sun pushes it up.
Overall, the forces balance each other so that the sun does not collapse or scatter. But the forces don’t cancel out perfectly everywhere, and Dr. Parker’s calculations show that the sun can act like a leaky balloon.
If you put enough pressure in the system, said Stuart Bale, a physicist at the University of California, Berkeley, the atmosphere can escape. And as it flees, it becomes energized.
In a paper published Wednesday in the journal Nature, Dr. Bale, who drives an instrument on the Parker Solar Probe that measures electric and magnetic fields in the solar wind, and his colleagues reported that the solar wind fluxes match patterns of hot gas rising and colder falling within the sun. This convection phenomenon, essentially the same thing that occurs in a thunderstorm, produces up-and-down flows of hydrogen within the sun, and the pattern of flows like thunderstorms packed close together is known as supergranulation.
The convection of charged particles generates changing magnetic fields that stretch until they break apart and reconnect, releasing energy that contributes to heating of the corona. That reconnection appears to accelerate solar wind particles.
Previous observations of the sun have already indicated that the solar wind exits what are known as coronal holes, regions where the magnetic field continues far outward into space instead of looping around and back at another point on the sun.
Imagine a simple bar magnet, which generates a magnetic field similar in shape to the one that surrounds the Earth. At the poles, magnetic fields go straight up and down; those are the coronal holes.
During quiet periods of the sun solar activity varies on an 11 year cycle, from relatively quiet to hyperactive the sun’s magnetic field has this magnetic bar configuration. When Parker probe was launched, the sun was near its minimum.
But as the sun approaches its cycle maximum, when the magnetic field is in the throes of reversing direction, the structure of the field becomes more complex and more coronal holes appear.
Parker spacecraft instruments detected that the solar wind was not uniform over the coronal holes. Instead, the particles emerged in micro-flows, like jets from a shower.
Space probe sensors began to see that the solar wind had a tremendous amount of structure, said James Drake, a physics professor at the University of Maryland and another author on the Nature paper.
The periodic pattern of the microflows matched that of supergranulation, suggesting that magnetic reconnection near the sun’s surface plays a key role in particle acceleration.
I could understand all the features of reconnection, Dr. Drake said. I could understand how much heating was going on. And once we figured out how much heating, I found it was enough to power the wind.
He added, “We didn’t have it at all before.”
Gary Zank, director of the Center for Space Plasma and Aeronomic Research at the University of Alabama in Huntsville, said the new findings are a crucial and important step in answering the conundrum of why the solar corona is a million degrees hotter. warm compared to its own relatively cold surface. Dr. Zank was not involved in the research but was one of the scientists who reviewed the article for the editors of Nature.
He basically says, “Here’s the mechanism by which we can begin to understand how that energy transfer occurs,” Dr. Zank said.
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