‘Knocking on eternity’s door’ — NASA’s Voyager mission turns 40

NASA’s Voyager mission celebrates 40 years in space this year, and humanity has much to thank it for.

Voyager brought to Earth the first close-up views of Uranus and Neptune. It revealed "spokes" in the rings of Saturn and details of Jupiter’s storm that had never been seen or even imagined. It imaged Io’s volcanic plumes and found the potential for life on the moons Enceladus and Titan.

In 2012, Voyager 1 left our solar system and entered interstellar space. It is the most distant man-made object from Earth and continues to collect and transmit valuable information to scientists — still using its antiquated 8-track tape recorder. 

“For me, the best thing about this anniversary and the celebration that everyone seems to be making of it, is just to have the opportunity to spend some time remembering what we all accomplished so long ago with so very little,” says Carolyn Porco, a planetary scientist and former member of the Voyager imaging team.

“In my mind, the Voyager mission is the Apollo 11 of the planetary exploration program,” she continues. “It has earned that iconic stature in our culture, because not only did it open up the solar system for our view, but it carried with it a record of human greetings and songs and pictures of our planet that constitute a message from humanity to the Milky Way, to whatever, whoever, finds Voyager — if ever. They will know, by looking at not only the construction of the spacecraft, but this record, that there was an intelligent civilization that put this together, and sent it on its way, and it was sent across space into the future. And it will very likely live for billions of years. It could do that. Certainly the Voyager record could do that.”

The vast majority of the solar system, Porco points out, exists beyond the orbits of the asteroids that surround our nearest planets. “Where we live — the Earth, Venus, Mars, Mercury, our neighbors — there’s virtually nothing here,” she says. “We’re nestled in close to the sun, but our solar system exists out there, and we could not have claimed to know what our own solar system was like until we had a mission that toured the outer solar system in the way that Voyager did. So, Voyager blew the doors off the house and opened up the view of our solar system.”

NASA launched the two Voyager spacecraft in 1977: Voyager 2, on Aug. 20, and Voyager 1 on Sept. 5.

What’s so remarkable to remember, Porco says, is how little scientists knew about Jupiter and Saturn, the main targets of the mission, when they launched Voyager. “We didn’t know how they were structured; their rotation rates, at least for Saturn, were not clear. … We knew nothing about what we were eventually going to find in the rings of Saturn,” Porco says.

As for Uranus and Neptune, which were the secondary goals of the NASA scientists (although they, by and large, kept this fact to themselves during the planning), “that was the hinterlands,” Porco says. Even the most powerful telescopes on Earth revealed only “fuzzy little dots, or at most a little blob of blue … Maybe we knew a moon or two. It was really venturing into uncharted territories. This is what is so monumental about what Voyager did.”

The most important targets for the Voyager 1 fly-by were Saturn’s rings, its globe and atmosphere, and Titan, the large moon that circles it. The rings were “one of the stars” of the Voyager mission and a stroke of good fortune for Porco.

“Just being confronted with [them] and seeing all the complexity in the rings was so mind-blowing,” she says. “I was lucky because there were so many new discoveries in the rings that two very important topics fell to me, a graduate student, to work on for my doctoral dissertation. That kind of defined what I would do for the rest of my life, because I ended up studying the very type of rings that were found in the late ’70s in circling Uranus.”

When Porco finished her PhD thesis, she was officially added to the Voyager imaging team to help plan the Uranus and Neptune encounters, because she had the knowledge required for studying Uranian rings, she explains.

Voyager 1 also revealed much new information about Saturn’s moon Titan, findings that helped NASA decide where to focus their attention on subsequent missions, like Galileo and Cassini.

Voyager 1’s success led to the decision to use Voyager 2 to pay closer attention to other major moons, and even more moons were discovered in the process, Porco says. Voyager 2’s discoveries showed NASA scientists that the moons could be as important to explore as any of the planets, because they might harbor life.

“We found that they could harbor oceans, and then subsequent missions, like Galileo at Jupiter, and, of course, Cassini at Saturn, found that there are moons around each planet that have subsurface oceans,” Porco says. “With Enceladus, the small moon that has a subsurface ocean at Saturn, we even know that it has all the basic ingredients for what we call in our business a habitable zone. It checks all the boxes for a body of water that we want to go back to and investigate further because it could — we’re not saying it does — but it could possibly harbor life.”

For Porco, Voyager’s benefits extend beyond the tangible discoveries. “Our explorations of our solar system have not only given us a perspective on ourselves and our cosmic place, but they have shown us how limited our thinking is until we go traveling,” she says. “In some sense, Voyager is the closest that humanity will ever come to immortality. People immediately registered with that. It moved people. It stirred people in such a way that people have such a fond feeling for this mission. In August of 2012, Voyager 1 entered interstellar space, and so Voyager defined us. It defined us as an interplanetary species during the 1980s and now it has defined us as an interstellar species. And so it will continue.”

“In about 2 to 10 years, depending how the power on the spacecraft is managed, it will wink off," Porco continues. "It will have no more power to send us any signals. It will be an enormously sad moment in history when that happens, but Voyager will continue long, long after. It could be long after humanity is gone.”

“Here’s another crazy thought that one of the producers [Timothy Ferris] of the Voyager record brought up,” Porco adds. “Perhaps billions of years from now, Voyager could be found. The record might be found and it could be found by a civilization that hasn’t even evolved yet. It’s like knocking on eternity’s door. That’s what Voyager has done for us.”

This article is based on an interview that aired on PRI’s Science Friday with Ira Flatow.