Neptune has 13 known moons. The largest by far is Triton,
discovered by William Lassell just 17 days after the discovery
of Neptune itself. It took a hundred years to discover the
second, Nereid. Triton orbits Neptune on a circular but
retrograde orbit. While retrograde orbits are common among
distant irregular satellites, Triton is a unique case of
retrograde moon so close to its planet. The third largest moon
of Neptune, Nereid follows a prograde but the most eccentric
orbit among the moons of the solar system, being at its
apocenter more than 7 times further from the planet than at its
pericenter. Two natural satellites discovered in 2002 and 2003,
Psamathe and S/2002 N 4, have the largest orbits of any natural
satellites discovered in the Solar system to date. They take 25
years to orbit Neptune at an average of 125 times the distance
between Earth and the Moon. It is likely that Neptune's inner
satellites are not the original bodies that formed with Neptune
but accreted rubble from the havoc that was wre