1980, 1981

Voyager Saturn Encounters

The Pioneer 11 robotic probe flyby of Saturn in 1979 was a dress rehearsal of sorts for an even more ambitious and detailed study of the planet’s atmosphere, moons, rings, and magnetic field by the NASA Voyager 1 and Voyager 2 probes, which were launched in 1977. Voyager 1 flew past Saturn in November 1980, and Voyager 2 followed close behind, in August 1981.

The Voyager Saturn encounters dramatically increased our knowledge about all of the diverse bodies and processes in the Saturn system. High-resolution imaging revealed details about the impact cratering record, composition, and geologic histories of the large icy moons Iapetus, Rhea, Tethys, Dione, Enceladus, Mimas, and Hyperion. Seven small new moons of Saturn were discovered in the Voyager images, several of which are embedded in what turned out to be a much more spectacularly complex ring system than had been previously imagined. Saturn’s rings were discovered to consist of thousands of individual rings and ringlets separated by thin gaps and kept organized by the gravity of a number of Shepherd Moons that co-orbit in the ring system.

Voyager data confirmed the telescopic and Pioneer 11 discovery that Saturn’s largest moon, Titan, has a thick and hazy atmosphere. Titan’s atmosphere was found to have more than 50 percent higher surface pressure than Earth’s (making it the solar system’s only moon with a thick atmosphere) and to be composed mostly of nitrogen. The orangish color of Titan’s haze was found to be caused by small amounts of methane, ethane, propane, and other organic molecules, some of which were predicted to exist as surface liquids at Titan’s very low temperature. Voyager’s cameras could not penetrate Titan’s haze to view the surface, however. Those discoveries would come some 15 years later, during the Cassini Saturn Orbiter and Huygens Titan Lander missions.

Voyager 1’s planetary exploration mission ended at Saturn. The probe’s trajectory was taken off its “Grand Tour” path (including a possible late-1980s flyby of Pluto) in order to fly it close enough to Titan to study its early Earthlike atmosphere in great detail. Voyager 1 is still operating some 120 astronomical units from the Sun and is the most distant object that humans have ever sent into the cosmos.

Mosaic of images obtained by Voyager 1 during its flyby of the Saturn system in November 1980. Six of Saturn’s largest moons are shown here: Dione (foreground), Tethys and Mimas (lower right), Rhea and Enceladus (upper left), and Titan (upper right).