Ed Stone, the scientist who led NASA’s Voyager breakthrough mission to the outer planets for 50 years and directed the Jet Propulsion Laboratory when it landed its first rover on Mars, died Tuesday. He was 88.
A physicist who got in on the ground floor of space exploration, Stone played a leading role in NASA’s missions to Mars, Jupiter, Saturn, Uranus and Neptune. Discoveries made under his watch revolutionized scientists’ understanding of the solar system and fueled humanity’s ambition to explore distant worlds.
Carolyn Porco, who worked on imaging on JPL’s Voyager and Cassini missions, called Stone “a very nice man” who was “as close to perfect as a project scientist could ever be.”
“When two science teams were at loggerheads over some spacecraft resources, and Ed had to decide between the two, even the guy who lost walked away thinking, ‘Well, if that’s what Ed decided, then that must be the answer. right,’” Porco said by email on 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 physics professor at Caltech in 1972 when he was asked to serve as chief scientist for a bold 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 hesitated because I was a fairly young professor at the time. I still had a lot of research I wanted to do,” he recalls 40 years later.
He took it anyway, and from the mission’s first Jupiter encounter in 1979 to its final flyby of Neptune in 1989, Stone became the scientific face of the Voyager mission. He led the science agenda and helped the public understand revolutionary images and data not only from Jupiter, Saturn, Uranus and Neptune, but from many of their fascinating moons.
Stone and more than 200 of his scientific collaborators were the first to discover lightning on Jupiter and volcanoes on its moon Io. They spotted 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 geysers on Neptune’s moon Triton.
“It seemed like everywhere we looked, as we encountered those planets and their moons, we were surprised,” Stone told the Los Angeles Times in 2011. “We were finding things we’d never imagined, gaining a clearer understanding of the environment of which the Earth was a part. e. I can close my eyes and remember every part of it.”
The Voyager 1 spacecraft became the first man-made object to reach interstellar space in 2012, and Voyager 2 followed suit in 2018.
Stone, pictured with a model of the Voyager spacecraft, said the discovery of volcanoes on Io was a highlight of the mission.
(NASA)
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 the two Voyager spacecraft. The fingerprints of his dedication and keen leadership are woven into 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 hardly the only one.
He was a principal investigator on nine NASA missions and a co-investigator on five others, including several satellites designed to study cosmic rays, the solar wind and Earth’s magnetic field.
He became director of the Jet Propulsion Laboratory at La Cañada Flintridge in 1991, a role he held for a decade.
It was an era of cost-cutting at NASA, but Stone still managed to launch the five-year Galileo mission to Jupiter and send the Cassini spacecraft to Saturn. He was also in charge of the agency when Mars Pathfinder delivered the Sojourner rover to the Red Planet. This marked the first time humans had placed a robotic rover on the surface of another planet.
Throughout his tenure at JPL, Stone continued to work and teach at Caltech, even teaching undergraduate physics during some of Voyager’s long interplanetary cruises.
He also served as chairman of the board of the California Assn. for Research in Astronomy, which is 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 older of two brothers, Stone was drawn to science at an early age. Under his father’s watchful eye, he learned how to take apart and reassemble all kinds of technology, from radios to cars.
“I’ve always been interested in learning why something is the way it is and isn’t the way it is,” Stone said an interviewer in 2018. “I wanted to understand, measure and observe.”
After studying physics at Burlington Junior College, he received his master’s and doctorate degrees at the University of Chicago. Shortly after he began his graduate studies, in 1957 news broke that the former Soviet Union had launched Sputnik, the world’s first artificial satellite.
“Like that, because of the Cold War and our need to deal with Sputnik, absolutely a whole new realm opened up,” he said.
Stone built a device for measuring the intensity of solar energetic particles above the atmosphere that made a trip into space on an Air Force satellite in 1961. Unfortunately the spacecraft’s transmitter malfunctioned, so only a very limited amount of data returned to Earth. However, it was still enough to show that the particle intensity was lower than expected.
Despite the transmitter glitch, Stone said the project was exciting. “We were taking the first steps into a whole new area of research and exploration,” he said. “We were right in the beginning.”
He joined the faculty at Caltech in 1964 and designed more space experiments, this time for NASA.
Stone’s particular area of interest was cosmic rays—high-velocity atomic nuclei that can come from explosive events in the Sun or from violent events beyond the solar system.
One of his cosmic ray experiments was included in Voyager’s 11 major experiments.
Ed Stone in 2011, about a year before Voyager 1 entered interstellar space.
(Al Seib / Los Angeles Times)
Peers praised Stone for his leadership of Voyager’s science team.
“He was a great hero, a giant among men,” Porco said, adding that Stone was known for treating everyone — from top scientists to graduate students — with respect.
Voyager team scientist Thomas Donahue put it this way: “Over the years, Ed Stone has proven himself to be remarkably good at keeping a pack 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 a $1.2 million prize. In 2012, his hometown of Burlington, Iowa, named the new one high school after him.
“This is truly an honor because it comes from the community where my journey of exploration began,” Stone said a local newspaper.
Decades after Voyager’s launch, he was asked to pick his favorite moment from the mission. He chose the discovery of volcanoes on Jupiter’s moon Io.
“To find a moon that is 100 times more volcanically active than the entire Earth is really quite surprising,” he said. “And that was typical of what Voyager would 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 grandchildren.