Neptune from Voyager 2 with Great Dark Spot at left and Small
Dark Spot at lower right. White clouds are composed of methane
ice; overall blue coloration is due at least in part to methane
absorption of red light. |Discovery date||23 September 1846|
|Semi-major axis||4,503,443,661 km |Orbital period||60,190.03
days 89,666 Neptune solar days |Synodic period||367.49 day|
|Average orbital speed||5.43 km/s| |Inclination||1.767975° to
Ecliptic 6.43° to Sun’s equator 0.72° to Invariable plane
|Longitude of ascending node||131.794310°| |Argument of
perihelion||265.646853°| |Equatorial radius||24,764 ± 15
km[b]Refers to the level of 1 bar (100 kPa) atmospheric
pressure</ref> |Polar radius||24,341 ± 30 km[b]
|Flattening||0.0171 ± 0.0013| |Surface area||7.6183×109 km2[b]
|Mean density||1.638 g/cm3[b]| |Equatorial surface
gravity||11.15 m/s2[b] |Escape velocity||23.5 km/s[b]| |Sidereal
rotation period||0.6713 day 16 h 6 min 36 s |Equatorial rotation
velocity||2.68 km/s |North pole right ascension||19h 57m 20s
|North pol