Edward Stone, 88, Physicist Who Oversaw Voyager Missions, Is Dead

Dr. Stone with a large-scale model of a Voyager spacecraft. He was director of the Jet Propulsion Laboratory in Pasadena, Calif., from 1991 to 2001. Caltech manages the lab for NASA.

Edward C. Stone, the visionary physicist who dispatched NASA’s Voyager spacecraft to run rings around our solar system’s outer planets and, for the first time, to venture beyond to unravel interstellar mysteries, died on Sunday at his home in Pasadena, Calif. He was 88.

His death was confirmed by his daughter Susan C. Stone.

Inspired by the launch of the Soviet satellite Sputnik in 1957, while he was a college student, Dr. Stone went on to oversee the Voyager missions 20 years later for the Jet Propulsion Laboratory, which the California Institute of Technology manages for NASA.

Twin aircraft, Voyager 1 and Voyager 2 were launched separately in the summer of 1977 from Cape Canaveral, Fla. Almost five decades later, they are continuing their journeys deep into space and still collecting data.

Dr. Stone was the program’s chief project scientist for 50 years, starting in 1972, when he was a 36-year-old physics professor at Caltech. He became the public face of the project with the double launch in 1977.

Taking advantage of a gravitational convergence of four planets that occurs only once every 176 years, the spacecraft soared past Jupiter, Saturn, Uranus and Neptune.

The spacecraft produced the first high-resolution images of the four planets, the rings of Jupiter, Uranus and Neptune, lightning on Jupiter and lava lakes that revealed active volcanoes on Jupiter’s moon Io.

“We were on a mission of discovery,” Dr. Stone told The New York Times in 2002. “But we didn’t appreciate how much discovery there would be.”

In 2012, Voyager 1 became the first human-made object to pass the heliopause frontier, where the fierce solar wind of subatomic particles yields to the force of other suns. Today, Voyager 1 is estimated to be 15 billion miles from Earth and traveling at a speed of 38,000 m.p.h., according to NASA. Voyager 2 crossed the border to interstellar space in 2018.

“The two spacecraft will be Earth’s ambassadors to the stars, orbiting the Milky Way for billions of years,” Dr. Stone once said.

His leadership on the Voyager project earned him the 1991 National Medal of Science from President George H.W. Bush.

As director of the Jet Propulsion Laboratory in Pasadena from 1991 to 2001, Dr. Stone oversaw the Mars Pathfinder mission and its wheeled Sojourner rover; the Galileo space probe’s orbital mission to Jupiter; the launch of the Cassini spacecraft to Saturn and its rings and moons, a joint project involving NASA, the European Space Agency and the Italian space agency; and a new class of Earth science satellites.

Dr. Stone also served, from the late 1980s through the ’90s, as chairman of the California Association for Research in Astronomy, which built and operated the W.M. Keck Observatory in Hawaii.

In 2014, he became the founding executive director of the Thirty Meter Telescope International Observatory, also in Hawaii. He held that position until 2022, when he retired as Voyager’s chief scientist.

In a statement, Thomas F. Rosenbaum, the president of Caltech, called Dr. Stone “a great scientist, a formidable leader and a gifted expositor of discovery.”

Edward Carroll Stone Jr. was born on Jan. 23, 1936, in Knoxville, Iowa, southeast of Des Moines, and grew up near Burlington, on the banks of the Mississippi River. His father, Edward Sr., owned a small construction company, and his mother, Ferne Elizabeth (Baber) Stone, kept its books.

“Our father was a construction superintendent who enjoyed learning new things and explaining how they worked,” Dr. Stone wrote when he was awarded the 2019 Shaw Prize in Astronomy for his work on the Voyager missions.

He received an associate of arts degree in physics from Burlington Junior College (now Southeastern Community College) and earned a master’s degree and a doctorate from the University of Chicago.

Dr. Stone married Alice Trabue Wickliffe in 1962. She died in 2023. In addition to his daughter Susan, he is survived by another daughter, Janet Stone; and two grandsons.

Shortly after he began his graduate studies, the news that the Soviets had launched a satellite focused his fascination with physics on space exploration and, in particular, cosmic rays, the particles that come from stars and that travel through the universe at warp speed.

Inspired by his doctoral adviser, John A. Simpson, Dr. Stone performed his first cosmic ray experiments in 1961 while working on Discover 36, an Air Force spy satellite.

He joined Caltech’s faculty in 1964. As chairman of the university’s Division of Physics, Mathematics and Astronomy, a role he held from 1983 to 1988, he helped establish the Laser Interferometer Gravitational-Wave Observatory, which later detected ripples in space and time called gravitational waves.

Norman Haynes, who for years was Voyager’s overall project manager, once said that Dr. Stone, by dint of his scientific expertise and management skill, “revolutionized the world of project science.”

In 1990, Dr. Stone acknowledged the irony in his signature project — that even with all its discoveries, he would not see its conclusion before he died.

“I’ve been having so much fun on Voyager,” he told The New York Times Magazine, “that even if I never see the edge of the solar system, I would do it all again.”

Dr. Stone eventually got to witness the twin spacecraft’s departure from the solar system — twice.

“I keep asking myself why is there so much public interest in space,” he said. “It is, after all, just basic science in the end. The answer is that it provides us with a sense of the future. When we stop discovering new things out there, the concept of the future will change. Space reminds us that there is something left to be done, that life will continue to evolve. It gives us direction, an arrow in time.”