If you've opened a fortune cookie, you've probably read an aphorism, like this one, 'The world may be your oyster, but that doesn't mean you'll get its pearl.' In just a few words this quote tells the reader a lesson about life, that you have nearly limitless possibilities, but not all of them lead to a great reward.
The exploration of Neptune has only begun with one spacecraft, Voyager 2 in 1989. Currently there are no approved future missions to visit the Neptunian system. NASA, ESA and also independent academic groups have proposed future scientific missions to visit Neptune.
For many, centuries people did not know that this planet even existed. It was discovered by Johann Galle and Heinrich D'Arrest in 1846. Neptune is the smallest of the four gas giants in our Solar System. Much like Saturn and Uranus, Neptune's atmosphere contains hydrogen, helium and methane.