Planet Neptune
Discovered by Johann Gotfried Galle Date of discovery September 23, 1846 Mass (kg) 1.024e+26 Mass (Earth = 1) 1.7135e+01 Equatorial radius (km) 24,746 Equatorial radius (Earth = 1) 3.8799e+00 Mean density (gm/cm^3) 1.64 Mean distance from the Sun (km) 4,504,300,000 Mean distance from the Sun (Earth = 1) 30.0611 Rotational period (hours) 16.11 Orbital period (years) 164.79 Mean orbital velocity (km/sec) 5.45 Orbital eccentricity 0.0097 Tilt of axis (degrees) 28.31 Orbital inclination (degrees) 1.774 Equatorial surface gravity (m/sec^2) 11.0 Equatorial escape velocity (km/sec) 23.50 Visual geometric albedo 0.41 Magnitude (Vo) 7.84 Mean cloud temperature -193 to -153C Atmospheric pressure (bars) 1-3 Atmospheric composition: Hydrogen 85%, Helium 13%, Methane 2% 
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