Two Hours Before Neptune . ... Credit Copyright: Voyager 2, NASA Explanation: Two hours before closest approach to Neptune in 1989, the Voyager 2 robot spacecraft snapped this picture . Clearly visible for the first time were long light-colored cirrus -type clouds floating high in Neptune's atmosphere . ... Most of Neptune's atmosphere is made of hydrogen and helium , which is invisible. ... Neptune has the fastest winds in the Solar System , with gusts reaching 2000 kilometers per hour. ...