Eugene N. Parker, the astrophysicist who predicted the existence of the solar wind, a continuous outpouring of charged particles traveling from the sun at a million miles per hour, died on Tuesday at his home in Chicago. He was 94.
His death was announced by the University of Chicago, where he had been a professor for decades.
In 2017, a NASA mission to fly through the outer wisps of the sun’s atmosphere was renamed after Dr. Parker. “He wrote the textbook on heliophysics,” said Thomas Zurbuchen, the associate administrator for NASA’s science directorate, who spearheaded the name change.
The solar wind, while continuous, can become violent when the sun throws out gigantic eruptions of particles known as coronal mass ejections. Those eruptions have the potential to induce electrical surges in power grids that could lead to continentwide blackouts.
“We know that what comes from the sun causes big impacts for us here at Earth,” Nicola Fox, director of heliophysics at NASA, said in a telephone interview.
When Dr. Parker published his prediction in 1958, almost no one believed him, including the reviewers of his paper and the editor of The Astrophysical Journal that published it.
“The prevailing view among some people was that space was absolutely clean, nothing in it, total vacuum,” Dr. Parker told The New York Times in 2018.
In response to the reviewers’ negative comments, he appealed to the journal’s editor, Subrahmanyan Chandrasekhar, who was also an astrophysicist at the University of Chicago. Dr. Parker argued that the reviewers had not pointed out any errors in his calculations, which described how the particles flowed from the sun like water spreading outward from a circular fountain.
“He went where the equations led him,” said Michael S. Turner, an astrophysicist at the Kavli Foundation in Los Angeles who was a longtime colleague of Dr. Parker’s at Chicago. “And they led him to some very interesting phenomena that people hadn’t discovered.”
Dr. Parker, he said, was happy when people pointed out a mistake in his calculations but not pleased when people accepted prevalent scientific assumptions without question.
“He had little patience for ‘It’s well known that …’” Dr. Turner said.
Even though Dr. Chandrasekhar, a future Nobel laureate, disagreed with Dr. Parker’s conclusions, he overruled the reviewers, and the paper was published.
Four years later, Dr. Parker was vindicated when Mariner 2, a NASA spacecraft en route to Venus, observed energetic particles streaming through interplanetary space — exactly what he had predicted.
When Dr. Zurbuchen joined NASA in 2016, the agency had been working for years on a mission called Solar Probe Plus, which was to swoop close to the sun repeatedly. Dr. Zurbuchen said he disliked the name Solar Probe Plus and wrote to the National Academies of Sciences, Engineering and Medicine asking it to suggest a person to name the mission after.
The unequivocal response: Eugene Parker.
NASA had never before named a spacecraft after a living person. But Dr. Zurbuchen, who had met Dr. Parker years earlier, said he did not have much trouble getting Robert Lightfoot, the acting administrator of NASA at the time, to approve the change in 2017. Dr. Zurbuchen then called Dr. Parker to ask if that would be all right with him. “He said, ‘Absolutely. It will be my honor,’” Dr. Zurbuchen recalled.
Dr. Parker later said he was surprised that NASA had asked for his permission.
A few months afterward, Dr. Parker went to visit the Johns Hopkins Applied Physics Laboratory in Maryland, where the spacecraft was built and tested. Dr. Fox, then project scientist for the mission, recalled saying, “Parker, meet Parker.”
The next year, Dr. Parker and his family traveled to Florida to watch the launch of his namesake spacecraft.
“There we go,” Dr. Parker said as the engines of a Delta 4 Heavy rocket lit up the early-morning skies around Cape Canaveral on Aug. 12, 2018.
“Parker was always understated,” said Dr. Zurbuchen, who was watching the liftoff near Dr. Parker that morning. “I only saw him cry twice. The first time, when he pulled up to the rocket and his name was on it, and after that launch, when it really got to him — the magnitude of what was happening.”
Months later, Dr. Fox traveled to Chicago to share some of the early data from the Parker probe with Dr. Parker. “His eyes literally lit up,” said Dr. Fox, who showed Dr. Parker photographs not of the sun itself but of dim particles to the side of the sun — the solar wind.
Dr. Fox arranged to send him preprints of papers that mission scientists were writing about the findings. “He read them and he sent notes on them,” she said. “He was just really, really excited about a mission that was really going to do all the science that he always wanted to do.”
Eugene Newman Parker was born on June 10, 1927, in Houghton, Mich. His father, Glenn, was an engineer at Chrysler; his mother, Helen (MacNair) Parker, was a homemaker.
After completing a bachelor’s degree in physics at Michigan State University in 1948 and a doctorate at the California Institute of Technology in 1951, Dr. Parker was an instructor and then an assistant professor at the University of Utah before moving in 1955 to the University of Chicago, where he remained for the rest of his academic career. He retired in 1995 but continued to publish articles and books.
Dr. Parker had not planned to study the sun, but his initial research at Chicago was a collaboration with John A. Simpson about cosmic rays. Although high-energy cosmic rays originate from distant galaxies, the thinking was that their collisions close to Earth could reveal something about what fills the space between planets in the solar system. That in turn led to solar physics.
Although the common wisdom among scientists in the 1950s was that space was empty, comets had already suggested otherwise. The gas and dust trailing from a comet does not flow behind it, as one might expect; instead, its direction always points away from the sun.
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 to supersonic speeds as it moved away.
Dr. Parker later turned to other research puzzles, like how the sun produces magnetic fields, the magnetic fields of galaxies and the structure of magnetized shock waves.
“He was Mr. Magnetism,” Dr. Turner said. “He was the expert on magnetism in the universe and understood it better than anyone else.”
His work did not rely on 20th-century physics breakthroughs like quantum mechanics or Albert Einstein’s theory of general relativity, but rather on older physics like Maxwell’s equations, devised by James Clerk Maxwell in the 1860s to describe the behavior of electric and magnetic fields.
“He found new and novel solutions,” Dr. Turner said, “and was brilliant at interpreting them.”
Dr. Parker received the National Medal of Science in 1989 and was a member of the National Academy of Sciences.
He is survived by his wife, Niesje Parker; a brother, Phillip; a son, Eric; a daughter, Joyce Marie Parker; three grandchildren; and two great-grandchildren.
One of the remaining mysteries of the sun is why its outer atmosphere is so hot. The surface of the sun is 10,000 degrees Fahrenheit. But that’s cool compared with the outer atmosphere known as the corona, where the wisps of gas are much sparser but much hotter — well over a million degrees.
In 1972, Dr. Parker proposed that a multitude of tiny solar flares — too tiny to be easily observed — were heating the corona. Dr. Fox remembered when she met with Dr. Parker the first time after the launch of the probe. “He nudged me and said very quietly, ‘Have you found any nanoflares yet?’” she said.
In 2020, researchers using data from two of NASA’s other sun-watching spacecraft reported that they might have observed nanoflares and that they had figured out how the energy could be turned to heat. At present, this is one of several hypotheses that might explain the superhot corona.
But as the Parker Solar Probe makes closer and closer approaches to the sun in the coming years, using flybys of Venus as a gravitational brake, it might pick up radio signals generated by nanoflares and prove Dr. Parker correct again.