Ed Stone, scientist who led the Voyager space missions through the solar system and beyond – obituary

Professor Ed Stone, who has died aged 88, was project scientist for Nasa’s Voyager 1 and Voyager 2 spacecraft missions from design and build to their launch, two weeks apart, in 1977.

Intended to explore the outer solar system with the exception of Pluto, Voyager 2 passed Neptune in 1989, sending back unprecedented data and photographs of alien worlds which stunned the astronomical community. To Stone’s astonishment, the two probes continued to function despite dwindling power supplies as they plunged on into the darkness beyond the planets for a further 33 years, and they continue collecting data today. Voyager 1 is now the most remote emissary of the human race, having left the Sun’s domain and entered the void between the stars of our galaxy.

Voyager was the brainchild of Gary Flandro, a summer student in the 1960s at Nasa’s Jet Propulsion Laboratory, who realised that the mid-1970s would offer a once-every-176 years opportunity for spacecraft to visit all four giant planets when they were in rare alignment.

The twin plutonium-powered spacecraft first visited Jupiter and Saturn, and Voyager 2 remains the only probe to have made fly-bys of Uranus and Neptune. The mission transformed our view of the solar system and raised the possibility that the conditions to support basic lifeforms may exist beyond Earth – and close enough to investigate.

Highlights have included beaming back the first glimpses of methane oceans on Titan, Saturn’s largest moon; ash-spewing volcanoes on Io, one of Jupiter’s moons; and a thunderstorm on Saturn. In addition they tracked 1,000 mph winds on the surface of Neptune and discovered five-mile-tall geysers erupting from the icy surface of Neptune’s largest moon, Triton.

“When I started on Voyager my two daughters were young,” Stone recalled in 2012. “By the time they were in college we had passed Saturn and were on our way to Uranus. They got married and the Voyagers just kept going, and we had grandchildren and Voyager just kept going and our grandchildren are now aware of what’s happening to the Voyagers just like our children were.”

By the time Stone retired from the mission in 2022, the Voyager spacecraft had travelled beyond the outer boundary of the heliosphere, the bubble of supersonic charged particles streaming outwards from the sun, and had ventured into interstellar space, where they continue to collect and transmit data to Earth.

By the mid-2020s the vessels will fall silent, but their journey will continue for billions of years, the spacecraft carrying with them a “compilation album” of what life was like when human beings roamed the Earth, featuring everything from Azerbaijani bagpipes, through the music of Beethoven and Chuck Berry to the sound of humpback whales and a message from Jimmy Carter – US president at the time the spacecraft were launched – for the interest and entertainment of alien civilisations they might encounter along the way.

The elder of two sons, Edward Carroll Stone was born in Knoxville, Iowa, on January 23 1936 and grew up in Burlington, Iowa, where his father ran a small construction company. After leaving school he studied physics at the University of Chicago, receiving a master’s degree in 1959 and a doctorate in 1964.

He then joined a former colleague, Rochus Vogt, in helping to launch a space physics programme at the California Institute of Technology, Pasadena, where he was appointed professor in 1976 and chaired the university’s physics, maths and astronomy division in the mid-1980s.

Stone went on to design scientific instruments for US satellites, oversaw the construction of the WM Keck Observatory in Hawaii and led the establishment of LIGO (Laser Interferometer Gravitational-Wave Observatory), a billion-dollar project that in 2015 made the first direct observations of gravitational waves, ripples in space time that scientists had been looking for for years.

In 1991 Stone was appointed head of Nasa’s Jet Propulsion Laboratory in La Cañada Flintridge, California, and continued to work on missions that included Mars Pathfinder, which landed the Sojourner rover on Mars in 1997; Galileo, which orbited Jupiter for eight years; Cassini, which orbited Saturn for 13 years, and the Parker Solar Probe, which flew through the corona, the sun’s upper atmosphere, in 2021.

He was awarded the US National Medal of Science in 1991 and the Shaw Prize in Astronomy in 2019.

Stone is survived by two daughters. His wife Alice died in December.

Ed Stone, born January 23 1936, died June 9 2024