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.
From its discovery in 1846 until the subsequent discovery of Pluto in 1930, Neptune was the farthest known planet. Upon Pluto's discovery, Neptune became the penultimate planet, save for a 20-year period between 1979 and 1999 when Pluto's elliptical orbit brought it closer to the Sun than Neptune.