Exploration of Neptune

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. Some mission plans are still active, while others have been abandoned or put on hold.

Neptune has also been scientifically studied from afar with telescopes, primarily since the mid 1990s. This includes the Hubble Space Telescope but most importantly ground-based telescopes using adaptive optics.

After having visited Saturn successfully, it was decided to continue and fund further missions by Voyager 2 to Uranus and Neptune. These missions were conducted by the Jet Propulsion Laboratory and the Neptunian mission was dubbed "Voyager Neptune Interstellar Mission". Voyager 2's observation phase of Neptune began 5 June 1989, the spacecraft officially reached the Neptunian system on 25 August and the data collection stopped 2 October.

On 25 August, in Voyager 2's last planetary encounter, the spacecraft swooped only 4,950 kilometres (3,080 mi) above Neptune's north pole, the closest approach it made to any body since it left Earth in 1977. When the spacecraft visited the Neptunian system, Neptune was the farthest known body in the Solar system. It was not until 1999, that Pluto was further from the Sun in its trajectory. Voyager 2 studied Neptune's atmosphere, Neptune's rings, its magnetosphere, and Neptune's moons. The Neptunian system had been studied scientifically for many years with telescopes and indirect methods, but the close inspection by the Voyager 2 probe settled many issues and revealed a plethora of information that could not have been obtained otherwise. The data from Voyager 2 are still the best data available on this planet in most cases.

The exploration mission revealed that Neptune's atmosphere is very dynamic, even though it receives only 3% of the sunlight that Jupiter receives. Winds on Neptune were found to be the strongest in the Solar System, up to three times stronger than Jupiter's and nine times stronger than the strongest winds on Earth. Most winds blew westward, opposite the planets rotation. Separate cloud decks were discovered, with cloud systems emerging and dissolving within hours and giant storms circling the entire planet in 16–18 hours in the upper layers. Voyager 2 discovered an anticyclone dubbed the Great Dark Spot, similar to Jupiter's Great Red Spot. However, images taken by the Hubble Space Telescope in 1994, revealed that the Great Dark Spot had disappeared. Also seen in Neptune's upper atmosphere at that time was an almond-shaped spot designated D2, and a bright, quickly moving cloud high above the cloud decks, dubbed "Scooter".

...
Wikipedia