Edward S. Stone, the visionary physicist who sent NASA’s Voyager spacecraft to orbit the outer planets of our solar system and first ventured into interstellar mysteries, died Sunday at his home in Pasadena, California. 88.
His death was confirmed by his daughter, Susan S. Stone.
Inspired by the launch of the Soviet Sputnik satellite in 1957 while an undergraduate, Dr. Stone went on to direct the Voyager missions 20 years later for the Jet Propulsion Laboratory, which Caltech runs for NASA.
The twin spacecraft, Voyager 1 and Voyager 2, were launched separately in the summer of 1977 from Cape Canaveral, Florida. Almost five decades later, they continue their journeys deep into space and are still collecting data.
Dr. Stone was the program’s chief project scientist for 50 years, beginning in 1972, when he was a 36-year-old professor of physics at Caltech. He became the public face of the project with the double launch in 1977.
Taking advantage of the gravitational convergence of four planets, which happens 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, Jupiter’s lightning bolts 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 many discoveries there would be.”
In 2012, Voyager 1 became the first man-made object to cross the heliopause boundary, where the fierce solar wind of subatomic particles gives way to the power of other suns. Today, Voyager 1 is estimated to be 15 billion miles from Earth and traveling at a speed of 38,000 mph, according to NASA. Voyager 2 crossed the boundary of 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 of the Voyager project earned him the National Medal of Science in 1991 from President George HW Bush.
As director of the Jet Propulsion Laboratory in Pasadena from 1991 to 2001, Dr. Stone directed the Mars Pathfinder mission and its Sojourner wheeled rover; the orbiting mission of the Galileo spacecraft 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 to the 1990s as chairman of the California Association for Research in Astronomy, which built and operated the WM Keck Observatory in Hawaii.
In 2014, he became the founding executive director of the International Thirty Meter Telescope Observatory, also in Hawaii. He held this 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 great leader and a gifted interpreter 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 (Beber) Stone, kept her books.
“Our father was a construction foreman who loved to learn new things and explain how they worked,” Dr. Stone wrote as he received the 2019 Shaw Award in Astronomy for his work on the Voyager missions.
He earned an associate’s degree in physics from Burlington Junior College (now Southeastern Community College) and earned an M.A. and Ph.D. from the University of Chicago.
Dr. Stone married Alice Trabue Wycliffe in 1962. She died in 2023. In addition to his daughter, Susan, he is survived by another daughter, Janet Stone; and two grandchildren.
Shortly after he began his graduate studies, news that the Soviets had launched a satellite focused his fascination with physics on the study of space and, in particular, cosmic rays, the particles that come from stars and travel through the universe at warp speed.
Inspired by his doctoral advisor 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 the Caltech faculty in 1964. As chairman of the university’s Department of Physics, Mathematics, and Astronomy, a role he held from 1983 to 1988, he helped establish the Laser Interferometer Gravitational-Wave Observatory, which -later discovered ripples in space and time called gravitational waves.
Norman Haynes, who for many years was Voyager’s overall project manager, once said that Dr. Stone, with his scientific expertise and management skills, “revolutionized the world of project science.”
In 1990, Dr. Stone acknowledged the irony of his landmark project—that even with all his discoveries, he would not see its end before he died.
“I had so much fun on Voyager,” he told The New York Times Magazine, “that even if I never saw the edge of the solar system, I would do it again.”
Dr. Stone ended up witnessing the twin spacecraft lift off from the solar system – twice.
“I keep asking myself 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. When we stop discovering new things there, the concept of the future will change. The cosmos reminds us that there is more to be done, that life will continue to evolve. It gives us direction, an arrow in time.
