WASHINGTON: Eugene Parker, a pioneering American astrophysicist who developed a mathematical model predicting the stream of charged particles from the Sun known as solar wind, has died aged 94, NASA said on Wednesday.

Parker, who in 2018 became the first person to witness the launch of a spacecraft bearing his name, was hailed as a visionary who laid the groundwork for the field of heliophysics, the science of understanding the Sun and its interactions with Earth and the solar system, including space weather.

“We were saddened to learn the news that one of the great scientific minds and leaders of our time has passed,” said NASA Administrator Bill Nelson in a statement. Parker died Tuesday, according to the University of Chicago.

Born on June 10, 1927 in Michigan, Parker earned a bachelors degree in physics from Michigan State University and a PhD from Caltech, then taught at the University of Utah before settling at the University of Chicago, his longtime home, in 1955.

He began studying the temperature of the Sun’s corona, and his calculations showed the conditions should produce a supersonic flow of particles off the surface.

The idea was initially met with skepticism — even ridicule. It only saw publication in the Astrophysical Journal when then editor and future Nobel prize winner Subrahmanyan Chandrasekhar realized he could not find a flaw in Parker’s math, and overrode the objections of two reviewers.

The theory was proved correct in 1962 when NASA’s Mariner II spacecraft encountered the stream of particles, called the solar wind.

Scientists now know that solar wind blankets all the planets, protecting them from harmful radiation, but also at times disrupting communications here on Earth when solar flares occur.

He also proposed the idea of “nanoflares” — small solar explosions that occur all over the Sun — which are responsible for the superheated corona, which was hotter than the surface, and couldn’t be explained by known physics at the time. Parker went on to study cosmic rays, the magnetic fields of galaxies and myriad other topics, and won numerous accolades including the US National Medal of Science, the Kyoto Prize, the Crafoord Prize and the American Physical Society Medal for Exceptional Achievement in Research.