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Pioneer 11 Becomes First Spacecraft to Reach Saturn on Sept. 1, 1979

Confirmed1 source · Sep 1, 2026

NASA's robotic probe, originally a Jupiter backup mission, used gravitational assist to reach Saturn and paved the way for later Voyager missions.

Pioneer 11 Becomes First Spacecraft to Reach Saturn on Sept. 1, 1979
Image via Space.com

What happened

On September 1, 1979, NASA's Pioneer 11 became the first spacecraft to fly by Saturn, passing within 13,000 miles of the planet's cloud tops. Launched in April 1973 as a backup to Pioneer 10, the probe initially traveled to Jupiter, then used gravitational assist to redirect toward Saturn, arriving four years and nine months later. During its encounter, Pioneer 11 deliberately flew through Saturn's outer rings to test whether the trajectory would be safe for the incoming Voyager probes. The spacecraft discovered several moons and a new ring, gathered evidence of Saturn's magnetic field, and captured 440 images during its encounter. Pioneer 11 photographed Titan and captured images of Jupiter's Great Red Spot during its earlier flyby. Despite being designed to last 21 months, Pioneer 11 functioned for 22 years, with NASA receiving its final signal on November 24, 1995, when the probe was 4 billion miles from Earth.

Context

Pioneer 11's mission was repurposed based on the success of Pioneer 10, which had proven that spacecraft could safely traverse the asteroid belt and survive Jupiter's radiation environment. This validation was critical because NASA planned to launch Voyager 1 and Voyager 2 in 1977 to tour the outer planets during a rare once-in-175-year planetary alignment. By establishing a safe trajectory through Saturn's rings and gathering data on the planet's atmosphere and magnetic field, Pioneer 11 directly enabled the subsequent Voyager missions to proceed with greater confidence. The probe also carried a message plaque designed by Carl Sagan, Frank Drake and Linda Salzman Sagan intended to communicate information about humanity to potential alien civilizations.