It's been 30 years since NASA's two Voyager spacecraft first visited Saturn, but the legacy of the discovery created by the probes still lingers at the ringed planet today.
Voyager 1 made its closest flyby of Saturn 30 years ago today (Nov. 12) and its sister craft, Voyager 2, followed suit nearly a year later on Aug. 25, 1981. The two probes discovered six previously unknown ? and small ? moons, offered a glimpse into the dynamics of Saturn's rings and confirmed that Titan, Saturn's largest moon, has a thick, nitrogen-rich atmosphere. [Images: Voyager's Photo Legacy.]
These findings alone opened astronomers' eyes to the richness of the Saturn system. But the Voyager encounters sparked so many new questions that another spacecraft, NASA's Cassini orbiter, was sent to probe those mysteries two decades later, researchers said.
"When I look back, I realize how little we actually knew about the solar system before Voyager," said Ed Stone of Caltech, a project scientist for the Voyager mission back in the day. "We discovered things we didn't know were there to be discovered, time after time."
While the Cassini mission has been a cooperative effort between NASA, Italy and the European Space Agency ? which built a Titan lander that rode piggyback on Cassini ? the twin Voyager probes launched in 1977 solely as NASA missions are, today, the spacecraft farthest from Earth.
Trailblazers at Saturn
Voyager 1's closest approach to Saturn in 1980 brought the probe to within 78,300 miles (126,000 kilometers) of the planet's cloud tops, and Voyager 2 came within 62,600 miles (100,800 km). The two close encounters ? part of a broader "grand tour" of the outer solar system ? revealed a Saturn scientists had never seen before. [Top 10 Voyager Probe Facts]
Voyager photos, for example, showed huge storms roiling Saturn's atmosphere ? something that Earth-based telescopes hadn't picked up, researchers said. And the spacecraft also discovered strange kinked patterns in Saturn's F ring, discovered only the year before by NASA's Pioneer 11 probe.
The two Voyagers also revealed that the surface of Enceladus, Saturn's sixth-largest moon, was surprisingly young in places, pointing toward recent geological activity.
Scientists used Voyager observations to resolve debates over whether Titan's atmosphere is thick or whisker-thin. The Voyagers found Titan to be shrouded in a thick haze of hydrocarbons in a nitrogen-rich atmosphere, leading scientists to predict that seas of liquid methane and ethane might dot the moon's surface, researchers said.
"It was clear Voyager was showing us something different at Saturn," Stone said. "Over and over, the spacecraft revealed so many unexpected things that it often took days, months and even years to figure them out."
Cassini: Saturn revisited
After the success of the Voyager flybys, Saturn was again alone until 1997. That was when NASA launched the Cassini spacecraft, which arrived at the ringed gas giant in 2004 and has been following up on Voyager's observations and blazing new trails ever since.
Cassini has helped astronomers answer some of the questions the Voyager flybys raised, NASA said in a statement. The probe has discovered a mechanism, for example, that explains the young terrain on Enceladus: tiger-stripe fissures that blast out jets of water vapor and organic particles.
Cassini has also revealed that Titan does indeed have stable lakes of liquid hydrocarbons on its surface, showing what a close analog that frigid moon may be to a young Earth. The probe has resolved how two small moons discovered by Voyager ? Prometheus and Pandora ? tug on the planet's F ring to create its strange, kinked shape, researchers added.
"Cassini is indebted to Voyager for its many fascinating discoveries and for paving the way for Cassini," said Linda Spilker, Cassini project scientist at JPL, who started her career working on Voyager. "On Cassini, we still compare our data to Voyager's and proudly build on Voyager's heritage."
Saturn mysteries still linger
Cassini's main mission to Saturn ended in 2008 and the expedition has been extended twice, with the probe scheduled to finish its studies of the planet in 2017.
That extension is key because the Voyager probes left a few mysteries that Cassini has still not yet solved.
For instance, scientists first spotted a hexagonal weather pattern when they stitched together Voyager images of Saturn's north pole. Decades later, Cassini obtained higher-resolution pictures of the odd weather formation, which suggests remarkably stable structure. But researchers still don't know what is causing the atmospheric oddity.
The two Voyager spacecraft launched in 1977 with the primary aim of exploring Jupiter and Saturn. But both probes kept on flying after accomplishing this task.
Between them, the two spacecraft explored the solar system's gas giants ? Jupiter, Saturn, Uranus and Neptune ? and 48 of the planets' moons, according to NASA officials.
Voyager 1 and 2 are still going, exploring the outer reaches of the solar system. They've both made it to the outermost layer of the heliosphere, where the solar wind is slowed by the pressure of interstellar gas. Voyager 1 is about 11 billion miles (17 billion km) from the sun, while Voyager 2 is about 9 billion miles (14 billion km) away, researchers said.
Even as the most distant human-built objects in space, both Voyager probes are still making scientific observations and beaming data home, according to NASA officials.
- Gallery: Voyager's Photo Legacy
- Top 10 Voyager Facts
- Gallery: Cassini's Latest Discoveries