Neptune is the “newest” of the major worlds, only being discovered in 1846 after theoretical predictions were made given irregularities in the orbit of Uranus. Its observation was a triumph of Newtonian gravitation theory, a feat that was tried again later to detect a planet pre-named Vulcan that were causing discrepancies between Mercury’s orbit and theoretical calculations. This attempt failed however, and the peculiarities were later explained by general relativity.
Modern Exploration of Neptune:
- Voyager 2 (1989) – NASA flyby mission, to date the only probe sent to the ice giant. It therefore provided the only closeup shots of Neptune and its major moon Triton, along with other smaller moons. Investigated the atmosphere and rings of Neptune, while also discovery the Great Dark Spot.