Mean distance from Sun: 30.06 Astronomical Units
4,497,000,000 km
Diameter: 49,500 km
Mass: 17.23 Earths
Density: 1.7 grams per cubic centimeter
Surface temperature: Less than -250 F
Orbital period: 164.79 years
Rotational period: Approximately 17 hours, 50 minutes

Similar in size and composition to Uranus, the eighth planet is so far from Earth that ground-based observations reveal little detail. Voyager 2 data confirm the presence of a tenuous ring system. Neptune's largest moon, Triton, may be glimpsed in telescopes of apertures of 30 cm.