In astronomy, the largest of Neptune's moons
and one of the four largest in the solar
system. It has a diameter of 2,720 km/1,690
mi, and orbits Neptune every 5.88 days in a
retrograde (east to west) direction. Its
surface has many fault lines and a bright
polar region that reflects 90% of the
sunlight it receives. Its atmosphere is
composed of methane and nitrogen, and has a
pressure only 0.00001 that of the Earth at
sea level. Triton was discovered by Galle
1846, one month after the discovery of
Neptune. Other surface features include what
appear to be frozen lakes, perhaps formed
when material ejected from Triton's interior
froze in low-lying areas of the surface.
Chemical reaction between the material on
Triton's surface and solar radiation are
probably responsible for the pinkish
colouring across the southern hemisphere. The
low number of craters suggests that the
surface may be fairly young on the geological
time scale, perhaps less than 500 million
years. It is possible that Triton may still
be volcanically active. Dark streaks near its
south pole may be formed from liquid nitrogen
thrown up into the atmosphere to heights of
several tens of kilometres, becoming frozen
and then being blown by gentle winds and
deposited across the surface. The features
resemble streaks seen elsewhere in the solar
system.