A satellite of Neptune, ninth from the planet at a distance of 5 513 818 km, orbital period 360.13 days; also known as Neptune II. Its orbit is one of the most elliptical of any satellite in the Solar System, with an eccentricity of 0.75, and is inclined at 7°.1 to Neptune’s equator. Nereid’s diameter is 340 km. It was discovered in 1949 by G. P. Kuiper.