In 1981, Voyager 2's visit to Saturn completely changed the hunt for aliens
The hunt for habitable worlds owes a debt to this moment in planetary science history.
Forty years ago, NASA scientist Linda Spilker started sleeping at the office. It was her first job out of college, but she wasn’t camping out because she was over-worked and chained to her desk. Instead, she was waiting for an exquisite moment in human history: The first time Voyager 2 would fly by Saturn and its moons, and, critically, the images it would return to Earth of the distinctive ringed planet.
“I’d bring my sleeping bag into my office, and I’d have like a timeline of when the pictures would come back to the Earth,” she recalls for Inverse. “A lot of people did this, so you could sometimes go into somebody’s office, and you might see a pair of feet sticking out from under the desk.”
Voyager 2’s flyby wasn’t the first time a spacecraft gave scientists a close-up view of the gas giant and its moons — that privilege went to its sister spacecraft Voyager 1, which entered the Saturn system on November 12, 1980.
But the flyby, which took place on August 26, 1981, provided scientists here on Earth with important observations that, combined with those of Voyager 1, have informed every NASA mission to the Saturn system since.
“We could go in and tweak the designs and the observations for Voyager 2.”
NASA’s Cassini, Huygens, and, importantly, the upcoming Dragonfly mission to Saturn’s moon Titan to search for signs of life all owe a debt to this moment in history.
What Voyager 2 discovered around Saturn — When Spilker graduated with a bachelor’s degree in physics and went to work for NASA in 1977, they gave her a choice of missions., including a brand new mission set to launch that year — Voyager.
“When they told me that Voyager was headed to Jupiter and Saturn, and possibly onto Uranus, and Neptune, I said, ‘Sign me up,’” she says.
Spilker watched Voyager 2 launch in August of 1977 and then settled into her role on the science team for both space probes until they reached the Saturn system. Voyager 1 made it on November 12, 1980, and just a little shy of one year later, Voyager 2 entered the Saturn system on August 26, 1981.
“The first flyby was unique in that we found so many interesting new things. We got to see the detailed structure, for instance, in Saturn’s rings,” Spilker says. With these data in hand, the scientists on the ground could plan for the next flyby — and what they wanted to find.
“We could go in and tweak the designs and the observations for Voyager 2,” Spilker says.
Voyager 2 took a closer look at Saturn’s rings, particularly the narrow, outermost “F” ring.
“We saw a lot of changes in that ring, in particular, these sorts of kinks and braids that we could see in that ring,” Spilker says.
Voyager 2 revealed that Saturn’s rings are anything but “bland sheets of material,” but rather intricate, detailed, and dynamic structures. Spilker would later use Voyager 2’s stellar and radio occultation data — measurements of how starlight and radio waves were influenced by the rings while passing through them — to complete her Ph.D. in geophysics and space physics.
“The way the waves damp out tell you something about the surface mass density and about the densities of particles,” she says.
“We saw evidence of tectonic fractures, softened craters.”
“I was always a big fan of the rings after having used so much ring data for my thesis.”
Identifying habitable worlds — Less visually beautiful, but perhaps more intellectually curious, were the observations collected by Voyager 2 of two of Saturn’s moons, Titan and Enceladus. These data would inform both later NASA missions and the scientific search for alien life.
Enceladus is now known to harbor a global liquid water ocean beneath its icy crust, making it a prime candidate target to search for extraterrestrial life. But before the Voyager craft made it to Saturn, scientists were not even sure the small, 500-kilometer diameter world was geologically active — a key ingredient for life.
“What was really astonishing was to see Enceladus and just how bright and pristine this world looked,” Spilker says.
“We saw evidence of tectonic fractures, softened craters,” she recalls.
NASA’s 2005 Cassini mission conducted multiple flybys of the little moon and took images of geysers erupting from Enceladus’s southern polar region. Cassini even flew through the geysers’ plumes, sampling what is believed to be water spewing up from the subsurface ocean.
Meanwhile, the surface of Saturn’s largest moon, Titan, remained obscured by haze during the Voyager missions. But the data Voyager 1 and 2 collected was then used to better equip the Cassini spacecraft and the Huygens lander, which separated from Cassini to land on Titan on January 14, 2005.
Together, they revealed a world of hydrocarbon lakes and water ice. Titan, scientists confirmed, was another intriguing candidate for hosting extraterrestrial life.
“All the things we learned with Voyager informed us and helped us build the Huygens probe,” Spilker says. She would know, as she joined the Cassini team in 1988.
“Had we not had that information from Voyager, it might have been much harder to put together.”
How Voyager 2 still influences NASA missions to Saturn — Voyager to Cassini and Huygens — each science mission informs the next, according to Planetary Scientist Elizabeth Turtle. Turtle is the primary investigator on the upcoming Dragonfly mission to Titan set to launch in the mid-2030s.
“Titan has been doing prebiotic chemistry experiments for us.”
“Each mission provides information that is the basis for future missions,” she says. “But each mission also raises questions, and those become the questions the next missions try to tackle.”
One of the big mysteries about Titan following the Voyager mission’s flyby was what lay on the moon’s surface. Cassini and Huygens answered that question, making observations that revealed a dense atmosphere rich in complex carbon molecules and a surface made of water ice. Turtle says these could include the ingredients necessary for the chemical reactions that could lead to the genesis of life.
Now it’s Dragonfly’s turn to answer the follow-up question as to whether or not those ingredients are indicative of signs of life on Titan.
An octocopter drone, Dragonfly will fly from place to place to sample the surface of Titan.
“Titan has been doing prebiotic chemistry experiments for us,” Turtle says. “What dragonfly is designed to do is to get there and pick up the results of those experiments and tell us whether there are biologically relevant compounds on the surface of Titan.”
How Voyager 2 keeps on keeping on — As for Voyager and Spilker, they have both left planetary science far behind. Earlier this year, Spilker rejoined the Voyager 2 mission as its deputy project scientist. Only now, instead of studying Saturn's rings, she’s studying the interstellar medium 150 astronomical units from the Sun: Voyager 2 officially left the Solar System on November 5, 2018.
“I think the goal is to keep taking as much science data for as long as we can,” Spilker says of the Voyager 2 spacecraft, which is now in its 44th year of operations.
“It’s gonna be a long time until we ever get another mission as far from the Sun as Voyager.”
Spilker recalls a statement made by Richard Laeser, then the Voyager project manager, after the Saturn flyby. “Voyager is in its post-retirement years,” Laeser said, and “is very healthy for its age.”
“I just had to chuckle,” Spilker says, “Because that was in 1985, and here we are in 2021, and the Voyagers — both of them are still going strong.”