The
Exploration of Neptune
started on August 25, 1989, when
Voyager 2
became the first and so-far only spacecraft to visit the planet. Like the other gas giants,
Neptune
has no solid land on its surface so landing on Neptune would be impossible.
NASA
is thinking to send another spacecraft known as the
Neptune Orbiter
to study more about Neptune; the spacecraft is planned to be probably launched on 2035. It would release atmospheric probes, and possibly release a Triton Lander.
NASA
has said the earliest possible launch date is 2030. Budget cuts may eliminate this proposal.
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In Voyager 2's last visit with a planet before leaving the
solar system
, Voyager 2 came 3000 miles (5000 km) above Neptune's north pole, the closest approach it made to any planet after it left
Earth
. Voyager 2 studied
Neptune's atmosphere
, its
rings
, its
magnetosphere
, and its
moons
. Several discoveries were made, including the discovery of the
Great Dark Spot
and
Triton
's geysers.
Voyager 2 found that Neptune's atmosphere was very active, even though it gets only 3% of the sunlight
Jupiter
receives. Voyager 2 discovered an
anticyclone
called the
Great Dark Spot
, similar to Jupiter's
Great Red Spot
. However, pictures taken by the
Hubble Space Telescope
showed that the Great Dark Spot had disappeared. Also seen in Neptune's atmosphere at that time was an
almond
-shaped spot called "
D2
", and a bright, quickly moving cloud high above the cloud decks named
Scooter
.
Voyager 2 also found four
rings of Neptune
and found proof for
ring arcs
, or incomplete rings around Neptune. Neptune's magnetosphere was also studied by Voyager 2. The planetary radio astronomy instrument found that Neptune's day is sixteen hours, seven minutes. Voyager 2 also discovered
auroras
, like on
Earth
, but much more complicated.
Voyager 2 discovered
six moons
orbiting Neptune, but only three were photographed in detail:
Proteus
,
Nereid
, and
Triton
. Proteus turned out to be an
ellipsoid
, as large as an ellipsoid could become without turning into a
sphere
. Proteus is very dark in color. Nereid, although discovered in 1949, is still not well known even after Voyager 2 passed by. Triton was flown by at about 25,000 miles (40,000 km) away, and became the last object Voyager 2 would ever explore. Triton was shown to have extraordinary active
geysers
and
polar caps
. A very thin atmosphere was found, as well as thin clouds.