420 km
ESTIMATED DIAMETER
1.12 DAYS
ORBITAL PERIOD
117,600 km
AVERAGE DISTANCE FROM NEPTUNE
1989
DISCOVERED
DARK
SURFACE
IRREGULAR
SHAPE
THE DARK MOON
Proteus is the second-largest moon of
Neptune and one of the largest irregular
satellites in the Solar System.
It was discovered in images taken by
Voyager 2 during its flyby of Neptune
in 1989.
Proteus has a dark surface and an
irregular, heavily cratered shape.
Its appearance suggests that it has
experienced many impacts throughout
its history.
The moon is not perfectly spherical
because its gravity is not strong enough
to pull its material into a rounded shape.
Proteus orbits Neptune relatively close
to the planet and completes one orbit
in just over one Earth day.
PROTEUS FEATURES
HEAVILY CRATERED
Proteus has a surface covered with
impact craters created by collisions
with other objects.
IRREGULAR SHAPE
Its gravity is not strong enough to make
the moon spherical, giving Proteus its
distinctive irregular appearance.
VOYAGER 2
Proteus was discovered when Voyager 2
photographed the Neptune system
during its historic 1989 encounter.
DID YOU KNOW?
Proteus is larger than some spherical
moons, but it remains
irregularly shaped
because its gravity is too weak to pull
it into a sphere.
IMAGE:
NASA / JPL / VOYAGER 2
PROTEUS IMAGE VIA WIKIMEDIA COMMONS
PROTEUS IMAGE VIA WIKIMEDIA COMMONS