Two Hours Before Neptune
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 . Shadows of these clouds can even be seen on lower cloud decks. Most of Neptune's atmosphere is made of hydrogen and helium , which is invisible. Neptune's blue color therefore comes from smaller amounts of atmospheric methane , which preferentially absorbs red light. Neptune has the fastest winds in the Solar System , with gusts reaching 2000 kilometers per hour. Speculation holds that diamonds may be created in the dense hot conditions that exist under the clouds-tops of Uranus and Neptune.