Animation of the Voyager 2 spacecraft passing Neptune. Voyager 2 was launched in August 1977, taking advantage of a rare planetary alignment to visit the four outer planets in the Solar System. It arrived at Neptune in August 1989, finding huge storm systems, including the Great Dark Spot seen here, and the fastest winds in the Solar System in its upper atmosphere. It used the gravity of Neptune to change its course to pass the largest moon, Triton, where it discovered cryovolcanism, including geysers of liquid nitrogen. After this encounter with Triton, Voyager 2 continued on that path, and is due to leave the Solar System entirely around 2019.