Ed Stone, head of the Voyager mission that introduced us to solar system's outer planets, has died

The NASA project scientist who led the grandest and farthest tour humanity's ever taken in our solar system has died. Ed Stone, the former director of the Jet Propulsion Laboratory and Voyager project scientist, was 88 years old when he died on June 9.

For five decades, Stone led the Voyager mission, the longest robotic space mission in history and one of the greatest journeys of discovery in modern times.

"How do you say goodbye to someone who helped make your destiny possible? Thank you, Ed, for opening the door for our celestial exploration. You will forever be remembered as your legacy lives on beyond the heliosphere," NASA said on its Voyager social media account, which is often written in the point-of-view of the spacecraft itself.

I was fortunate to witness the entire Voyager mission personally from launch through to the encounters with the four largest planets in our solar system: Jupiter, Saturn, Uranus and Neptune. The twin spacecraft were built and controlled at the Jet Propulsion Laboratory in Pasadena, Calif., where I made regular pilgrimages over the 12 years that the encounters took. 

At every close encounter with the giant planets, Stone would be our guide. He led daily press conferences to report on the health of the spacecraft, give an overview of the events that had happened that day and introduce the various team leaders.

They would each show the latest images or data from the spacecrafts' radio observations of the planets, but also their moons that were being seen up close for the first time — some of which we didn't even know existed until Voyager discovered them. It was just a taste of the flood of data the Voyager spacecraft were sending back.  

At each morning press conference, Stone was first to speak. Like a child on Christmas morning, he would unwrap new photos of alien landscapes which human eyes had never seen before.

Both Voyagers spacecraft flew past Jupiter in 1979 and over the rings of Saturn in 1980 and 1981. Then, Voyager 2 flew past the sideways-spinning planet Uranus in 1986 and out to the blue orb of Neptune in 1989 — to date, it's the only spacecraft to ever do so.

Now, more than 20 billion kilometres from the sun, both spacecraft have reached interstellar space.

These visits were brief flybys — the spacecraft didn't stop at any destination or go into orbit around a planet or land on the surface. They just swept by like tourists who never get off the bus, taking as many photos and other measurements as possible before heading off to the next destination.

Ed Stone first joined the Voyager mission in 1972 and remained leader until he retired in 2022. During that time he managed dozens of scientists working on different teams that operated the suite of instruments aboard the spacecraft.  

During these brief flybys, which only lasted a matter of days, conflicts would arise between the science teams over what the spacecraft would do during the limited amount of time available. Some wanted to get images of particular moons while another team preferred to measure magnetic fields or plasmas. Stone was the level-headed arbitrator and final decision maker, and his judgment helped make the Voyager mission a success far beyond expectations.

Stone's career was not limited to Voyager. He was director of the Jet Propulsion Laboratory from 1991 to 2001, and was part of nine NASA missions including Mars Pathfinder which carried Sojourner, the first rover to land on Mars; the Cassini mission that orbited Saturn; and the Parker Solar Probe that flew through the corona of the sun. 

Stone was also a professor at the California Institute of Technology which in 2023 established the endowed Edward C. Stone Professorship in his honour.  

When I interviewed him for Quirks & Quarks in 2017 on the 40th anniversary of Voyager's launch, and again in 2019 when Voyager 2 reached interstellar space, his enthusiasm for the mission and his eloquence explaining it was undiminished.

I had hoped to speak to him again for the 50th anniversary of Voyagers launch in 2027. He will be deeply missed by the scientific community and journalists alike, to whom he was always accommodating. 

It has been a tremendous honour to have been witness to this journey of pure discovery with Ed Stone at the helm.