Eugene N. Parker predicted the existence of solar wind in 1958. The NASA spacecraft, scheduled to launch on Saturday, is the first named for a living person.
CHICAGO — It was 1958. Sputnik had launched only a year earlier, the first human-made object to circle the planet. But the beach ball-size spacecraft had no instruments to measure anything in space.
The study of what was up there was largely limited to what scientists could observe from the ground. It certainly looked like the vast expanses between planets were empty. And that is what most scientists believed.
But not Eugene N. Parker, then a 31-year-old, no-name professor at the University of Chicago. In a foundational paper published in The Astrophysical Journal, Dr. Parker described how charged particles streamed continuously from the sun, like the flow of water spreading outward from a circular fountain.
Almost no one believed him.
“The prevailing view among some people was that space was absolutely clean, nothing in it, total vacuum,” Dr. Parker recalled during an interview at his home.
The scientists who had reviewed the paper rejected his idea as ludicrous. Dr. Parker appealed to the journal’s editor, Subrahmanyan Chandrasekhar, a prominent astrophysicist also at Chicago, arguing that the reviewers had not pointed out any errors, just that they did not like the premise.
Dr. Chandrasekhar overruled the reviewers.
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Four years later, Dr. Parker was vindicated when Mariner 2, a NASA spacecraft en route to Venus, measured energetic particles streaming through interplanetary space — exactly what Dr. Parker had predicted.
Scientists now call that stream of particles the solar wind.
Sixty years after Dr. Parker’s paper, NASA is about to launch a spacecraft that is to dive into outer wisps of the sun’s atmosphere and gather information about how our star generates the solar wind.
It is the Parker Solar Probe, named after Dr. Parker, now 91 years old. It is the first time that NASA has named a mission for a living person.
Dr. Parker, two decades into his retirement from the University of Chicago, is frailer now than when he made a trip to the North Pole with his son Eric in 2004. His apartment here, overlooking the Museum of Science and Industry, is decorated with some of his intricate wood carvings.
He still gets around. Last October, he traveled to the Johns Hopkins Applied Physics Laboratory, where the spacecraft was built, for a “Parker, meet Parker!” encounter.
Four generations of Parkers have traveled to Florida watch the liftoff, scheduled for pre-dawn Saturday from Cape Canaveral Air Force Station during a 65-minute window that starts at 3:33 a.m. NASA TV will broadcast the launch beginning at 3 a.m. Eastern time.
Dr. Parker did not set out to revolutionize the science of the sun. He did not even have much interest in interplanetary science although he was seeking a research career. But academic jobs were scarce.
Dr. Chandrasekhar put in a good word for him when a Chicago physics colleague, John A. Simpson, was looking to hire someone to help study the mysterious particles known as cosmic rays. The thinking was that even though cosmic rays originate far away in other galaxies, the cascades of collisions they cause close to Earth might reveal something about the contents of the interplanetary neighborhood.
That led to solar physics. “I discovered it was a fascinating subject,” Dr. Parker said.
Since the 1800s, scientists did know that at least sometimes explosions from the surface of the sun affected Earth. That included one on Aug. 29,1859. That day, two English amateur astronomers, Richard Carrington and Richard Hodgson, independently observed a “white light flare” emanating from the surface of the sun. Less than a day later, Earth’s magnetic field was knocked awry. Across America and Europe, telegraph wires sparked and failed.
Fewer than 18 hours elapsed between the flare and the geomagnetic storm on Earth. That meant whatever had exploded off the sun must have traveled at more than 5 million miles per hour.
Scientists had no idea what that might be.
Comets provided another clue. The tail of gas and dust coming from a comet does not flow behind the comet as one might expect, but instead its direction always points away from the sun.
A German astronomer, Ludwig Biermann, suggested that particles emitted from the sun — what he called solar corpuscular radiation — were shaping the comet tails. (“Corpuscular” is a fancy word that means “consisting of tiny bits of something.”)
“That is an important piece of information,” Dr. Parker said. “All comet tails have this property so in all directions at all times, the sun is emitting something or other.”
Dr. Parker’s crucial insight was that this flow of particles would follow the same dynamics as wind and water.
The calculations showed that the flow started slow near the sun and accelerated as it moved farther away, passing Earth at supersonic speeds. “That really stuck in people’s craw,” he said.
That is what he wrote down in his 1958 paper. “It was widely disbelieved,” Dr. Parker said. “I even had people say, ‘Well, you know, it was a great idea, too bad it was wrong.’ I said, ‘I don’t see why it’s wrong.’”
The skepticism did not worry him. Fluid dynamics is a direct derivation from Newton’s laws of motion.
After Mariner 2, “everyone agreed the solar wind existed,” Dr. Parker said.
While Dr. Parker moved on to other problems in astrophysics, a close-up visit to the sun has been on NASA’s to-do list since the 1950s. Over the decades, various sun-watching spacecraft have observed the sun, but always from a distance.
In 2005, at NASA’s request, engineers at Johns Hopkins Applied Research Laboratory in Laurel, Md. proposed the Solar Probe, a mission that would swoop within 1.8 million miles of the sun. But it would have cost more than $1 billion at the time and it required a plutonium power source t hat NASA didn’t want to use. Because of the intense heat, the mission would have been over after two flybys.
NASA sent the engineers back to see if they could trim the price tag to under $750 million and eliminate the plutonium. To do that, the spacecraft would not fly as close. But that had a major benefit; the spacecraft would make 24 orbits instead of two, gradually moving inward, and gather much more data.

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