page_title: Exploration of Neptune
section_title: Voyager 2
hierarchical_section_title: Exploration of Neptune / Voyager 2
caption_attribution_description: Voyager 1 / Voyager 2 English: NASA photograph of one of the two identical Voyager space probes Voyager 1 and Voyager 2 launched in 1977. The 3.7 metre diameter high-gain antenna (HGA) is attached to the hollow ten-sided polygonal body housing the electronics, here seen in profile. The Voyager Golden Record is attached to one of the bus sides. The angled square panel below is the optical calibration target and excess heat radiator. The three radioisotope thermoelectric generators (RTGs) are mounted end-to-end on the left-extending boom. One of the two planetary radio and plasma wave antenna extends diagonally left and down, the other extends to the rear, mostly hidden here. The compact structure between the RTGs and the HGA are the high-field and low-field magnetometers (MAG) in their stowed state; after launch an Astromast boom extended to 13 metres to distance the low-field magnetometers. The instrument boom extending to the right holds, from left to right: the cosmic ray subsystem (CRS) above and Low-Energy Charged Particle (LECP) detector below; the Plasma Spectrometer (PLS) above; and the scan platform that rotates about a vertical axis. The scan platform comprises: the Infrared Interferometer Spectrometer (IRIS) (largest camera at right); the Ultraviolet Spectrometer (UVS) to the right of the UVS; the two Imaging Science Subsystem (ISS) vidicon cameras to the left of the UVS; and the Photopolarimeter System (PPS) barely visible under the ISS. Suggested for English Wikipedia:alternative text for images: A space probe with squat cylindrical body topped by a large parabolic radio antenna dish pointing upwards, a three-element radioisotope thermoelectric generator on a boom extending left, and scientific instruments on a boom extending right. A golden disk is fixed to the body.
context_page_description: The exploration of Neptune has only begun with one spacecraft, Voyager 2 in 1989. As of July 2020 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.
context_section_description: 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 started taking navigation images of Neptune in May 1988. Voyager 2's observation phase proper of Neptune began 5 June 1989, the spacecraft officially reached the Neptunian system on 25 August and the data collection stopped on 2 October. Initially it was planned to use a trajectory that resulted in Voyager 2 passing around 1,300 km (810 mi) from Neptune and 8,200 km (5,100 mi) from Triton. The need to avoid ring material detected by stellar occultations resulted in this trajectory being abandoned and a trajectory that largely avoided the rings but resulted in more distant flybys of both targets.
  On 25 August, in Voyager 2's last planetary encounter, the spacecraft swooped only 4,950 km (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".
  The fly-by of the Neptunian system provided the first accurate measurement of Neptune's mass which was found to be 0.5 percent less than previously calculated. The new figure disproved the hypothesis that an undiscovered Planet X acted upon the orbits of Neptune and Uranus.
  Neptune's magnetosphere was also studied by Voyager 2. The magnetic field was found to be highly tilted and largely offset from the planet's centre. The  probe discovered auroras, but much weaker than those on Earth or other planets. The radio instruments on board found that Neptune's day lasts 16 hours and 6.7 minutes. Neptune's rings had been observed from Earth many years prior to Voyager 2's visit, but the close inspection revealed that the ring systems were full circle and intact, and a total of four rings were counted.
  Voyager 2 discovered six new small moons orbiting Neptune's equatorial plane, and they were named Naiad, Thalassa, Despina, Galatea, Larissa and Proteus. Only three of Neptune's moons were photographed in detail: Proteus, Nereid, and Triton; of which the last two were the only Neptunian moons known prior to the visit. Proteus turned out to be an ellipsoid, as large as gravity allows an ellipsoid body to become without rounding into a sphere. It appeared very dark in color, almost like soot. Nereid, though discovered in 1949, still has very little known about it. Triton was revealed as having a remarkably active past. Active geysers a
caption: Voyager 2 spacecraft
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