On this day in space! Aug. 20, 1977: Voyager 2 launches to the outer planets

On Aug. 20, 1977, NASA launched the Voyager 2 spacecraft on a mission to explore the outer planets. Despite its name, this was the first of the two Voyager missions NASA launched that year. Voyager 2: Sailing Among Giant PlanetsThanks to a rare alignment of the planets, NASA had the opportunity to send a spacecraft on an unprecedented journey to Jupiter, Saturn, Uranus and Neptune.While Voyager 1 ended its planetary mission after Saturn, Voyager 2 completed a 12-year journey to Neptune. But they didn't stop there! Voyager 1 left the solar system and entered interstellar space in 2012, and Voyager 2 followed suit in 2018. As it approaches 50 years of operation, the probe continues to return data from three functioning science instruments. NASA's Voyager 2 launched on Aug. 20, 1977. (Image credit: NASA)Why it matteredNearly half a century later, it remains the only spacecraft to visit all four has giants in our solar system, and the only spacecraft humanity has ever sent past Uranus and Neptune. Some of Voyager 2’s biggest surprises came from the moons orbiting those planets. Its images of Neptune’s largest moon, Triton, revealed active geyser-like plumes blasting nitrogen miles above the surface — making it one of only three geologically active moons in the solar system (maybe four, depending on what Europa Clipper finds).Decades beyond its original mission, Voyager 2 has begun studying the Kuiper Belt environment beyond the Sun’s protective heliosphere, giving scientists measurements from a region no spacecraft had been designed to reach. Voyager 2's plutonium power supply drops in efficiency about four watts per year, and NASA engineers were recently able to reduce how much power Voyager 2 needs by switching off a number of non-science components to adapt a less demanding method of warming the spacecraft while it continues traveling ever farther away from the sun.