His death was announced by the California Institute of Technology, where he was professor emeritus of physics, and NASA’s Jet Propulsion Laboratory, which he directed for 10 years starting in 1991. His daughter, Susan Stone, said he had been in poor health but that the cause of death was not yet known.
Dr. Stone began his career in physics at the dawn of the space age and turned his attention to space after the Soviet Union launched Sputnik—the shiny metal ball that became the world’s first artificial satellite—while he was a graduate student at the university. Chicago in 1957.
Over the next six decades, he designed some of the first scientific instruments for American satellites; he oversaw the construction of the WM Keck Observatory, which boasted two of the largest optical telescopes in the world when completed in Hawaii in the mid-1990s; and spearheaded the founding of LIGO, the billion-dollar physics experiment that in 2015 made the first direct observations of gravitational waves, ripples in space-time that had eluded scientists for years.
He remains best known for serving as project scientist—and less officially as chief spokesman—for Voyager 1 and 2. The twin probes, which were launched two weeks apart in 1977, five years after Dr. Stone, brought back fascinating photographs of the giant outer planets and their moons, as well as a wealth of data about the solar system.
“We were on a mission to discover,” he told the New York Times in 2002, looking back on the project’s beginnings. “But we didn’t appreciate how many discoveries there would be.
Both probes visited Jupiter and Saturn, with Voyager 2 continuing on to Uranus and Neptune, aided by a rare alignment of the outer planets that occurs once every 176 years. One-ton probes now travel through interstellar space, farther than any other man-made object in space. Along with cameras and scientific instruments, each carries a celestial message in a bottle: a gold-plated record, designed with the help of astronomer Carl Sagan, carrying sounds and images that would introduce potential aliens to the diversity of life on Earth. .
“It was a wonderful idea,” said Dr. Stone in 2011 to the Los Angeles Times when considering including the footage as Voyager 1 prepared to enter interstellar space. “However, at the time I was only focused on the journey to Saturn.
Beginning in 1979, the probes took the first detailed images of Europa, one of Jupiter’s moons, revealing a cracked, broken surface of the frozen world that “looked like an ice pack,” as Dr. Stone. They studied the vast ring system of Saturn; found evidence of a thick atmosphere rich in organic compounds on Saturn’s moon Titan; tracked 1,000 mph winds in impacts on Neptune’s surface; and discovered five-mile-tall geysers erupting from the icy surface of Neptune’s largest moon, Triton.
One of the mission’s most notable early findings was the discovery of volcanic activity on Jupiter’s moon Io. It was the first time active ash-spewing volcanoes had been discovered outside Earth, and it surprised scientists who had assumed the moon would be much like Earth — inert, cratered, cold and dead.
“From time to time we have found that nature is much more resourceful than our models,” said Dr. Stone to Caltech interviewers.
As Voyager passed the outer planets, Dr. Stone on the nightly news and gave frequent interviews. While overseeing 11 investigative teams and about 200 researchers, he was instrumental in accelerating the pace at which the team’s scientists reported their findings, leading daily meetings to identify the group’s most interesting findings, and then working with researchers to help create material accessible to the general public .
“He was like this machine,” his one-time boss, Norman Haynes, who served three years as Voyager’s chief project officer, told the New York Times in 1990. He walked around all day doing things.’
Astronomer Bradford A. Smith, who led the team that interpreted Voyager’s photographs, told a newspaper in 2002 that the flood of images and data sent back by the probes made Voyager “the most successful mission NASA has ever done” — praise that has been repeated. by many scientists over the years.
“What we know about the outer planets is a direct result of Ed Stone’s contribution,” A. Thomas Young, former director of NASA’s Goddard Space Flight Center, once said. “He was one of two or three people who got Voyager moving.
Voyager’s success helped get Dr. Stone became more widely known, leading to his appointment as head of the Jet Propulsion Laboratory, or JPL, the famous planetary science center managed for NASA by Caltech. The laboratory faced budget cuts due to the Cold War, although Dr. Stone still managed to work on major missions that included Mars Pathfinder, which landed on Mars with the Sojourner rover in 1997; the Galileo spacecraft, which orbited Jupiter for eight years; and Cassini, which orbited Saturn for 13 years.
A tribute from the lab noted that Dr. Stone was a rare scientist involved in the mission that traveled farthest from the Sun—Voyager—as well as the mission that came closest to the Sun: the Parker Solar Probe, which flew through the corona. , the Sun’s upper atmosphere, in 2021.
“I keep asking myself why there is such public interest in space,” said Dr. Stone of the New York Times before taking over at JPL. “It’s just basic science after all. The answer is that it gives us a sense of the future. When we stop discovering new things out there, the concept of the future changes. The universe reminds us that there is more to be done, that life will continue to evolve. It gives us direction, an arrow in time.”
The eldest of two sons, Edward Carroll Stone Jr. was born in Knoxville, Iowa, on January 23, 1936. He grew up in Burlington, Iowa, where his father ran a small construction business that his mother helped run. His parents encouraged his early fascination with science, including his efforts to take his transistor radio apart and put it back together.
“I was always interested in why something is the way it is and not the other way around,” recalled Dr. Stone. “I wanted to understand and measure and observe.
After graduating from Burlington Junior College (now Southeastern Community College) in 1956, he enrolled at the University of Chicago, where he earned a master’s degree in 1959 and a doctorate in physics in 1964. By then he had married Alice Wickliffe, a classmate at UChicago. She died in December. Survivors include their two daughters, Susan and Janet Stone, and two grandchildren.
With a doctorate in hand, Dr. Stone joined one of his former UChicago colleagues, Rochus “Robbie” Vogt, to help start the space physics program at Caltech. Appointed full professor in 1976, he chaired the Physics, Mathematics, and Astronomy Division in the mid-1980s, around the same time he began work on Keck, a complex of two 10-meter telescopes near the summit of Mauna Kea in Hawaii.
His work on the project led him to push for the proposed Thirty Meter Telescope, an even larger observatory that scientists hoped to build nearby. Construction was halted due to protests by Native Hawaiians and other critics who oppose development at the site.
Colleagues described Dr. Stone as shy and single-minded, with few interests outside of physics. “My work is my relaxation,” he liked to say. He continued to work on Voyager for decades, juggling teaching and research duties while collecting honors including the National Medal of Science in 1991 and the Shaw Prize in Astronomy in 2019, before retiring from the mission in 2022.
By this time the probes had traveled far beyond the orbits of Neptune and Pluto. Voyager 1, the more distant of the two, is now more than 15 billion miles from Earth and is still operational, although engineers have had to come up with solutions for malfunctioning computer chips and other communication problems. The spaceship and its twin eventually run out of power, though Dr. Stone proudly noted that the probes would “go on forever,” drifting through space with their golden payloads and silent instruments.
“As far as what happens to me, nature will have its way, I understand,” he told the Los Angeles Times in 2011. “Even if I’m not there, we’re going to keep exploring, we’re always finding out the science. I’m optimistic about this.”