How solar wind flows from the sun like water from a shower head

High-speed particles spew out from the sun like water from a shower head, scientists reported Wednesday.

Data from the Parker Space Probe, a NASA spacecraft launched in 2018 and now diving in to collect measurements of the sun’s outer atmosphere, or corona, provides clues to how the sun generates the solar wind — a million miles a day. hour hour stream of electrons, protons and other charged particles rushing outward into the solar system.

The solar wind research ties into a mystery that has long baffled scientists: Why is the corona, where temperatures reach millions of degrees, so much hotter than the sun’s surface, which is a relatively cool 10,000 degrees Fahrenheit?

The Parker probe 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 tenuous gases that are dragged downwards by gravity, while the pressure generated by fusion reactions in the sun pushes upwards.

In general, the forces are balanced so that the sun does not collapse or blow apart. But the forces don’t cancel out perfectly everywhere, and Dr. Parker how the sun can behave like a leaky balloon.

“If you put enough pressure on the system,” says Stuart Bale, a physicist at the University of California, Berkeley, “the atmosphere can escape. And when it escapes, it gets energized.”

In a newspaper published on Wednesday in the journal Nature, Dr. Bale, who directs an instrument on the Parker Solar Probe that measures electric and magnetic fields in the solar wind, and his colleagues reported that the currents of solar wind correspond to patterns of hot gases rising and cooler gases invading the sun. This phenomenon of convection, essentially the same thing that occurs in a thunderstorm, produces up-and-down currents of hydrogen in the sun, and the pattern of currents — like thunderstorms packed side by side — is known as supergranulation.

The convection of charged particles generates shifting magnetic fields that stretch until they snap and reconnect, releasing energy that contributes to the corona’s heating. That reconnection seems to accelerate the solar wind particles.

Previous observations of the sun had already indicated that solar wind comes from so-called coronal holes, regions where the magnetic field goes far out into space instead of wrapping around and coming back down at another point on the sun.

Imagine a simple bar magnet generating a magnetic field similar in shape to the one surrounding the Earth. At the poles, the magnetic fields go straight up and down; those are the coronal holes.

During the sun’s quiet periods — solar activity varies on an 11-year cycle, from relatively calm to hyperactive — the sun’s magnetic field possesses this bar magnet configuration. When the Parker spacecraft launched, the sun was near its minimum.

But as the sun approaches the maximum of its cycle, when the magnetic field is in a reversing direction, the structure of the field becomes more complex and more coronal holes appear.

The Parker spacecraft’s instruments found that the solar wind was not uniform across coronal holes. Instead, the particles emerged in “microcurrents,” like jets from a shower head.

The spacecraft’s sensors “began to see that the solar wind had an enormous amount of structure,” said James Drake, a professor of physics at the University of Maryland and another author of the Nature paper.

The periodic pattern of the microcurrents matched that of the supergranulation, suggesting that near-surface magnetic reconnection plays a key role in the particle’s acceleration.

“I was able to figure out all the features of reconnection,” said Dr. Drake. “I was able to find out how much heating was going on. And once we figured out how much heating, I found out it was enough to drive the wind.

He added: “We didn’t have this 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 results were “a critical and important step in answering the puzzle of why the solar corona is a million degrees hotter compared to its very relatively cold surface.” Dr. Zank was not involved in the research, but he served as one of the scientists who reviewed the paper for Nature editors.

“It’s basically saying, here’s the mechanism by which we can begin to understand how that transfer of energy happens,” said Dr. Zank.