Voyagers Ready to Go Dark

W hen the two Voyager probes launched into space in 1977, they were headed to uncharted territory. It was the first time humanity had sent robot spacecraft to study up close the four giant outer planets of our solar system: Jupiter, Saturn, Uranus, and Neptune. Stunning images and scientific data captured by the probes over the next few decades altered our understanding of the cosmos. Through the Voyagers, we learned of Jupiter’s turbulent atmosphere, the tilted magnetic field of Uranus, a rotating storm on Neptune called the Great Dark Spot, and Saturn’s dynamic rings. We also discovered 23 new moons of the outer planets and found that these moons were not the dead, frozen worlds scientists had suspected. Saturn’s moons appeared to be composed mostly of water ice, while active volcanoes on Jupiter’s moon Io spewed lava dozens of miles high. Eventually, the two spacecraft would explore not just the four giant planets, but 48 of their moons, as well as the rings, atmospheres, and magnetic fields those planets possess.

Once the Voyagers’ tour of the four planets was complete in 1990, the world’s attention faded; but the probes continued to provide remarkable insights into the dynamics of the solar system, including ultraviolet sources among the stars and the boundary between the sun’s influence and interstellar space. Even today, both probes continue sending back data about the interstellar medium, the space between the stars, says Linda Spilker, NASA’s project scientist for the Voyager missions—including precise measurements of the density and temperature of the thin ionized gases it contains and the incidence of high-energy cosmic rays.

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