<html>
<head>
<title>Neptune Fact Sheet</title>
</head>
<body text="#337ABB" background="../images/stars">
<h3>Neptune Fact Sheet</h3>
<img src="../images/neptune">Neptune
<hr>
<h4>Neptune/Earth Comparison</h4>
<h5>Bulk parameters</h5>
<pre>
                                   Neptune      Earth   Ratio(Neptune/Earth)
Mass (10<sup>24</sup> kg)                     102.43      5.9736        17.147
Volume (10<sup>10</sup> km<sup>3</sup>)                    6,254   108.321         57.74 
Radius (1 bar level) (km)
    Equatorial                     24,766      6,378          3.883
    Polar                          24,342      6,356          3.830
Volumetric mean radius (km)        24,624      6,371          3.865
Ellipticity                         0.0171     0.0034         5.03
Mean density (kg/m<sup>3</sup>)                1,638      5,520          0.297
Gravity (eq., 1 bar) (m/s<sup>2</sup>)        11.00       9.78           1.125
Escape velocity (km/s)             23.5       11.19           2.10
GM (x 10<sup>6</sup> km<sup>3</sup>/s<sup>2</sup>)                   6.8351     0.3986        17.15 
Bond albedo                         0.82       0.385          2.13
Visual Geometric Albedo             0.41       0.367          1.12
Visual magnitude V(1,0)            -6.87      -3.86             -
Solar irradiance (W/m<sup>2</sup>)             1.47       1,380          0.00107
Black-body temperature (K)         33.2      247.3            0.134
J<sub>2</sub> (x 10<sup>-6</sup>)                      3411.      1082.63           3.151    
</pre>
<hr>
<h5>Orbital parameters</h5> 
<pre>
                                   Neptune      Earth   Ratio(Neptune/Earth)
Semimajor axis (10<sup>6</sup> km)           4,496.6       149.6        30.06
Sidereal orbit period (days)     60,189.        365.256     164.79   
Tropical orbit period (days)     59,799.9       365.242     163.73
Perihelion (10<sup>6</sup> km)               4,458.0       147.1        30.31      
Aphelion (10<sup>6</sup> km)                 4,535.2       152.1        29.82
Synodic period (days)               367.49        -             -
Mean orbital velocity (km/s)          5.48       29.79        0.184
Orbit inclination (deg)               1.773       0.00          -
Orbit eccentricity                    0.00858     0.0167      0.514
Sidereal rotation period (hours)     16.11*      23.9345      0.673
Obliquity to orbit (deg)             29.56       23.45        1.261
</pre>
<p>
* Magnetic coordinates (as determined by the Voyager 2 Radio Science experiment)
<hr>
<h4>Neptunian Magnetosphere</h4>

Goddard Space Flight Center OTD (O8) Model
<pre>
    Dipole field strength: 0.142 gauss-Rn<sup>3</sup>
    Dipole tilt to rotational axis: 46.9 degrees
    Longitude of tilt: 288 degrees (IAU convention)
    Dipole offset (planet center to dipole center) distance: 0.55 Rn
</pre>
<p>
<b>Note:</b> Rn denotes Neptunian radii, here defined to be 24,765 km
<hr>

<h4>Neptunian Atmosphere</h4>
<pre>
Surface Pressure: &gt;&gt;100 bars  
Average temperature: ~58 K
Temperature at 1 bar: ~72 K
Density at 1 bar: ~0.45 kg/m<sup>3</sup>
Wind speeds: 0-200 m/s
Scale height: 19.1 - 20.3 km
Mean molecular weight: 2.53 - 2.69 g/mole
Atmospheric composition
    Major:       Molecular hydrogen (H<sub>2</sub>) - 89%; Helium (He) - 11%
    Minor (ppm): Methane (CH<sub>4</sub>)
    Aerosols:    Ammonia ice, water ice, ammonia hydrosulfide, methane ice(?)
</pre>
</body>
</html>