Twelve years after launch, Voyager 2 passed within 3,000 miles of Neptune's cloud tops, sending back the first close-up images of the giant blue planet. The spacecraft discovered new moons, confirmed Neptune's rings, and revealed active nitrogen geysers on the moon Triton, the coldest object then measured in the solar system. It remains humanity's only visit to Neptune.
Voyager 2 had already toured Jupiter, Saturn, and Uranus by the time it reached Neptune, riding a rare planetary alignment that allowed a single spacecraft to visit all four gas giants using gravity assists. Engineers and scientists at JPL treated the Neptune encounter as an emotional finale; many had worked on the mission since its 1977 launch and understood no follow-up mission was likely for decades.
The images revealed a deep blue world marked by the Great Dark Spot, a storm system comparable to Jupiter's Great Red Spot, and winds clocked at over 1,300 miles per hour, the fastest recorded in the solar system. Neptune's moon Triton stunned scientists with active cryovolcanism, spewing nitrogen gas and dark material across its frozen, cantaloupe-textured surface despite surface temperatures near -235°C.
After Neptune, Voyager 2 continued outward, and in 2018 it crossed into interstellar space, joining its twin Voyager 1. The Neptune flyby data, transmitted across nearly 2.7 billion miles at the speed of light with a delay of over four hours, still represents the only spacecraft data ever collected at the planet, making every image an irreplaceable scientific record.