Why Voyager 1 skipped Pluto for Titan at Saturn in 1980

Voyager 1 made its closest approach to Saturn at 23:46 UT on November 12, 1980, passing about 78,000 miles (126,000 km) from the planet, but the flyby’s real prize was the giant moon Titan. To study it up close, NASA gave up any chance of sending Voyager 1 on to another world, Pluto included.

The Titan trade-off

NASA says Voyager 1 could have been aimed onward to Pluto, but exploring Titan and Saturn’s rings was a primary goal. Its route was designed to pass within about 2,550 miles of Titan, and that close pass bent its path northward out of the ecliptic, the plane in which most planets orbit. No further planetary encounters were possible.

The gamble also decided the fate of its twin. Voyager 2’s trajectory kept open an option to continue to Uranus and Neptune, and NASA let it go on only after Voyager 1 had successfully gathered its Titan data. Pluto had to wait until New Horizons flew past in July 2015.

Titan repaid the effort. Its thick atmosphere hid the surface completely and turned out to be about 90% nitrogen, with methane and more complex hydrocarbons that hinted at prebiotic chemistry. NASA’s mission fact sheet puts the surface at 94 kelvins (−292 °F) and 1.5 atmospheres, a denser blanket than Earth’s.

Saturn itself delivered too: Voyager 1 found five new moons, a new ring now called the G ring, and “shepherd moons” that keep some rings sharply defined. Its icy moons, from Mimas to Rhea, all appeared to be largely water ice.

After Saturn the probe headed north at about 3.5 AU a year, the escape route that made it, in 2012, the first spacecraft to leave the heliosphere.