TRITON is the largest of Neptune’s moons, and the seventh largest moon in the Solar System. It was discovered by British astronomer, William Lassel, on October 10, 1846, one month after the discovery of Neptune itself.

Triton is the coldest measured object in the Solar System, with a surface temperature of -235ºC. It is so cold that nitrogen in its atmosphere condences on its surface as frost. It is the only satellite in the Solar System known to have a nitrogen ice surface.

Triton’s atmosphere is very tenuous and is composed principally of nitrogen. The moon’s atmospheric pressure is only 15 microbars, or 0.000015 times the sea-level pressure on Earth.

Triton is locked into a synchronous orbit around Neptune, and so like Earth’s Moon always shows the same side to its primary. However, it is the only satellite in the Solar System which orbits its planet in a retrograde direction, that is contrary to Neptune’s rotation. Astronomers consequently believe that Triton was an object from the Kuiper Belt that was captured by Neptune’s gravitation.

Triton is a geologically active world, and has geyers which eject icy, mineral material onto its surface.


This image was taken in 1989 by NASA’s Voyager 2 spacecraft. The pinkish tint of the south polar cap is believed to be caused by traces of methane in the ice reacting to sunlight.

Average distance from Neptune: 354,759 km (219,965 miles)
Diametre: 2707 km (1,680 miles)
Orbital period: 5.87 days
Rotational period: 5.87 days