by Ed Stone, the scientist who led NASA’s pioneering Voyager mission to the outer planets for 50 years and headed the Jet Propulsion Laboratory, landed his first rover on Mars on Tuesday. He was 88.
A physicist who got in on the ground floor with space exploration, Stone played a key role in NASA’s missions to Mars, Jupiter, Saturn, Uranus and Neptune. The discoveries made on his watch revolutionized scientists’ understanding of the solar system and fueled humanity’s ambition to explore distant life.
Carolyn Porco, who worked on imaging on JPL’s Voyager and Cassini missions, called Stone “an amazingly beautiful man” who was “as close to perfect as a project scientist could ever be.”
“When two science teams were at odds over some spaceship capability, and Ed had to decide between the two, even the loser went away thinking, ‘Well, if this is Ed’s decision, it must be is the right answer,'” Porco said via email Tuesday. “I feel blessed to have known Ed. And like many people today, I’m very sad to know he’s gone.”
Stone was a 36-year-old Caltech physics professor in 1972 when he was asked to serve as chief scientist for an ambitious plan to send a pair of spacecraft to explore the four giant planets of the solar system for the first time.
It was the opportunity of a lifetime, but he wasn’t sure he wanted the gig.
“I was hesitant because I was a fairly young professor at that point. I still had a lot of research I wanted to do,” he recalled 40 years later.
He took it anyway, and from the mission’s first contact with Jupiter in 1979 to the final flyby of Neptune in 1989, Stone became the scientific face of the Voyager mission. He guided the scientific agenda and helped the public make sense of revolutionary images and data not only from Jupiter, Saturn, Uranus and Neptune, but from many of their fascinating moons.
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Stone and his more than 200 scientific collaborators were the first to discover lightning on Jupiter and volcanoes on its moon Io. They saw six never-before-seen moons around Saturn and found evidence of the largest ocean in the solar system on Jupiter’s moon Europa, as well as a geyser on Neptune’s moon Triton.
“It seemed like everywhere we looked, as we found these planets and their moons, we were surprised,” Stone told the Los Angeles Times in 2011. “We were finding things than we ever imagined, getting a clearer sense of the environment the Earth was a part of. I can close my eyes and still remember every part of it.”
The Voyager 1 spacecraft was the first man-made object to reach interstellar space in 2012, and Voyager 2 followed suit in 2018.
The twin probes continue to send weekly communications to Earth from interstellar space. Stone retired in 2022 on the mission’s 50th anniversary.
“A part of Ed lives on in both Voyager spacecraft. His dedication and enthusiastic leadership are imprinted on the Voyager mission,” said Linda Spilker, who joined the mission in 1977 and succeeded him as project scientist.
The Voyager mission was Stone’s crowning achievement, but it was hardly his only one.
He was principal investigator on nine NASA missions and co-investigator on five others, including several satellites designed to study cosmic rays, the solar wind and the Earth’s magnetic field.
He was appointed director of the Jet Propulsion Laboratory at La Canada Flintridge in 1991, a role he held for ten years.
It was an era of cost-cutting at NASA, but Stone still managed to send the five-year Galileo mission to Jupiter and the Cassini spacecraft to Saturn. He also led the agency when Mars Pathfinder took the Sojourner rover to the Red Planet. This was the first time humans had placed a robot on the surface of another planet.
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During his time at JPL, Stone continued to work and teach at Caltech, even teaching groundbreaking physics during some of Voyager’s long interplanetary cruises.
He was also chairman of the board of the California Assn. for Research in Astronomy, responsible for the construction and operation of the WM Keck Observatory and its two 10-meter telescopes on Mauna Kea, Hawaii.
Edward Carroll Stone Jr. was born. in Iowa on January 23, 1936, and grew up in Burlington, where his father ran a small construction business and his mother kept the company’s books.
The eldest of two brothers, Stone was drawn to science from an early age. Under his father’s watchful eye, he learned how to take apart and put together all kinds of technology, from radios to cars.
“I’ve always been interested in finding out why something is this way and not that way,” Stone said an interviewer in 2018. “I wanted to understand and measure and observe.”
After studying physics at Burlington Junior College, he received his master’s and doctorate at the University of Chicago. Shortly after starting his graduate studies, news arrived in 1957 that the former Soviet Union had launched Sputnik, the world’s first artificial satellite.
“Just because of the Cold War and our need to match Sputnik, a whole new area has completely opened up,” he said.
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Stone built a device to measure the intensity of energetic solar particles above the atmosphere that hit a trip to space aboard an Air Force satellite in 1961. Unfortunately the spacecraft’s transmitter did not work, so only a very limited amount of data was transmitted back to Earth. . However, it was still sufficient to indicate that the intensity of the particles was lower than expected.
Despite the transmitter glitch, Stone said the project was thrilling. “We were taking the first steps in a whole new area of research and exploration,” he said. “We were right at the start.”
He joined the faculty at Caltech in 1964 and created more space experiments, this time for NASA.
Stone’s particular area of interest was cosmic rays – high-speed atomic nuclei that can come from explosive events on the sun or from violent events outside the solar system.
One of his cosmic ray experiments was counted among Voyager’s 11 major milestones.
Stone’s colleagues praised him for his leadership of Voyager’s science team.
“He was a great hero, a giant among men,” Porco said, adding that Stone was known to everyone – from top scientists to graduate students – with respect.
Voyager crew scientist Thomas Donahue put it this way: “Over the years, Ed Stone has been incredibly adept at keeping a series of prima donnas on track.”
Stone was elected to the National Academy of Sciences in 1984 and received the National Medal of Science from President George HW Bush in 1991 in recognition of his leadership of the Voyager mission. He won the Shaw Prize in Astronomy in 2019, an honor that comes with an award of $1.2 million. In 2012 he named his hometown of Burlington, Iowa, his new hometown secondary school after.
“This is a great honor because it comes from the community where my journey of exploration began,” Stone tell local newspaper.
Years after Voyager’s launch he was asked to choose his favorite moment from the mission. He chose the discovery of volcanoes on Jupiter’s moon Io.
“Finding a moon that’s 100 times more volcanically active than the entire Earth is amazing,” he said. “And this was typical of what Voyager was going to do on the rest of its journey through the outer solar system.
“Time after time, we discovered that nature was much more inventive than our models,” he said.
His wife, Alice, whom he met on a blind date at the University of Chicago and married in 1962, died in December. The couple is survived by their two daughters, Susan and Janet Stone, and two grandsons.
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This story originally appeared in the Los Angeles Times.
