Edward Stone, 88, physicist who oversaw the Voyager missions, is dead

Edward C. Stone, the visionary physicist who sent NASA’s Voyager spacecraft to orbit the outer planets of our solar system and first ventured beyond to unlock the secrets of the interstellar system, died Sunday at his home in Pasadena, California. 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 still a college student, twenty years later Dr. Stone directed the Voyager missions for the Jet Propulsion Laboratory, operated by the California Institute of Technology for NASA.

The twin aircraft Voyager 1 and Voyager 2 were launched independently from Cape Canaveral, Florida, in the summer of 1977. Nearly five decades later, they continue their journey deep into space and are still collecting data.

Dr. Stone served as the program’s chief project scientist for 50 years, beginning in 1972 when he was 36 years old and a physics professor at Caltech. He became the public face of the project with the dual launch in 1977.

The spacecraft took advantage of the gravitational convergence of four planets, which only occurs every 176 years, and flew past Jupiter, Saturn, Uranus and Neptune.

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

“We were on a voyage of discovery,” Dr. Stone told the New York Times in 2002. “But we didn’t know how many discoveries there would be.”

In 2012, Voyager 1 became the first man-made object to cross the heliopause boundary, where the violent solar wind of subatomic particles gives way to the force of other suns. Today, NASA estimates Voyager 1 is 24 billion kilometers from Earth and traveling at a speed of 61,000 km/h. Voyager 2 crossed the boundary into interstellar space in 2018.

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

In 1991, he was awarded the National Medal of Science by President George HW Bush for his leadership of the Voyager project.

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

Dr. Stone also served as chairman of the California Association for Research in Astronomy, which built and operated the WM Keck Observatory in Hawaii, from the late 1980s through the 1990s.

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

In a statement, Thomas F. Rosenbaum, president of Caltech, called Dr. Stone “a great scientist, an impressive leader, and a gifted explainer of discoveries.”

Edward Carroll Stone Jr. was born on January 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 the books.

“Our father was a construction manager and loved learning new things and explaining how they worked,” Dr. Stone wrote when he was awarded the Shaw Prize in Astronomy in 2019 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, news of the launch of a Soviet satellite drew his attention to physics and directed his fascination toward space exploration and, in particular, cosmic rays, the particles emitted by stars that move through the universe at warp speed.

Inspired by his doctoral supervisor John A. Simpson, Dr. Stone conducted his first experiments with cosmic rays in 1961 while working on Discover 36, an Air Force spy satellite.

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

Norman Haynes, who served as Voyager’s overall project manager for many years, once said that Dr. Stone’s scientific expertise and management skills “revolutionized the world of project science.”

In 1990, Dr. Stone realized the irony of his most important project: despite all his discoveries, he would not live to see its completion until his death.

“I had so much fun on Voyager,” he told The New York Times Magazine, “that I would do it again even if I never saw the edge of the solar system.”

Finally, Dr. Stone witnessed the twin spaceships leaving the solar system – twice.

“I keep wondering why there is so much public interest in space,” he said. “After all, it’s just basic science. The answer is that it gives us a sense of the future. If we stop discovering new things out there, the concept of the future will change. Space reminds us that there is still work to be done, that life will continue to evolve. It gives us a direction, an arrow in time.”