Ed Stone is flying off into the sunset after 50 years as science chief of NASA's groundbreaking Voyager mission.
Stone has retired as the project scientist of Voyager, which sent twin probes on a historic "grand tour" of the solar system's giant planets and, much later, out to interstellar space. He had held the post since 1972 — five years before the launch of the twin spacecraft, which are still going strong.
"It has been an honor and a joy to serve as the Voyager project scientist for 50 years," Stone said in a NASA statement on Tuesday (Oct. 25).
"The spacecraft have succeeded beyond expectation, and I have cherished the opportunity to work with so many talented and dedicated people on this mission," he added. "It has been a remarkable journey, and I’m thankful to everyone around the world who has followed Voyager and joined us on this adventure."
Voyager 1 and Voyager 2 launched a few weeks apart in 1977 and headed for the realm of the giant planets. Voyager 1 flew by Jupiter in March 1979 and then zoomed past both Saturn and its largest moon, Titan, in November 1980.
Voyager 2 performed flybys of Jupiter and Saturn as well, visiting the two planets in July 1979 and August 1981, respectively. The probe then got humanity's first-ever up-close looks at our solar system's "ice giants," flying past Uranus in January 1986 and Neptune in August 1989.
These close encounters taught scientists a great deal. Voyager 1's Jupiter flyby, for example, revealed extensive volcanism on Io, which we now know is the most volcanically active body in the solar system. Voyager 2 discovered 10 new moons of Uranus and found a nitrogen-ice volcano on Triton, Neptune's largest satellite.
But there was more history to be made. Both Voyagers kept on flying, all the way to the edge of the heliosphere, the huge bubble of charged particles and magnetic fields that the sun blows around itself. Voyager 1 crossed the heliopause, which marks the end of the heliosphere, in August 2012, becoming the first human-made object ever to enter interstellar space. Voyager 2 followed suit in November 2018.
Voyager 1 is now about 14.7 billion miles (23.7 billion kilometers) from our planet, or roughly 159 astronomical units (AU). (One AU is the Earth-sun distance — about 93 million miles, or 150 million km). Voyager 2 is about 12.3 billion miles (19.8 billion km) away, or nearly 132 AU from us.
Both spacecraft are still operational, gathering unprecedented data about this exotic, far-flung realm. And the information that continues to come in is, in part, a testament to Stone, team members said.
"Ed likes to say that Voyager is a mission of discovery, and it certainly is," Voyager project manager Suzanne Dodd said in the same statement. "From the flybys of the outer planets in the 1970s and '80s to the heliopause crossing and current travels through interstellar space, Voyager never ceases to surprise and amaze us. All those milestones and successes are due to Ed’s exceptional scientific leadership and his keen ability to share his excitement about these discoveries to the world."
Linda Spilker will succeed Stone, becoming the Voyager mission's second-ever project scientist. She was a member of the Voyager science team during the planet flyby era before leaving to do other things, including becoming project scientist for NASA's Cassini Saturn mission. Spilker rejoined Voyager as deputy project scientist last year.
It's unclear if the Voyagers will join Stone in hitting the half-century mark. Their nuclear power source is fading, and mission team members have had to turn off some instruments over the past few years to save juice. The probes have enough power and thruster fuel to keep operating in their current state until at least 2025, NASA officials have said, but the future beyond that is murky.
Even after death, the probes will continue to be emissaries for humanity, their existence proof of our own. With this in mind, both Voyagers carry "golden records" designed to teach aliens about us, should E.T. happen to stumble across either probe.
Mike Wall is the author of "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or on Facebook.