Galileo first observed Neptune but mistook it for a star. In 1846, Galle and d'Arrest localized Neptune and it was initially called the planet exterior to Uranus. Friedrich von Struve later suggested the name Neptune. Neptune has a solid core and layers of ice, ammonia and water surrounding it. Its atmosphere contains hydrogen, helium and methane with wind speeds up to 2000 km/h. Voyager 2 was the only spacecraft to visit Neptune in 1989 and made discoveries about its magnetic field, weather and 13 moons including Triton.