Mercury Fact Sheet

Mercury

Mercury/Earth Comparison

Bulk parameters

                                   Mercury        Earth      Ratio (Mercury/Earth)
Mass (1024 kg)                      0.3301        5.9726     0.0553    
Volume (1010 km3)                   6.083       108.321      0.0562  
Equatorial radius (km)	            2439.7        6378.1     0.383      
Polar radius (km)                   2439.7        6356.8     0.384      
Volumetric mean radius (km)         2439.7        6371.0     0.383
Ellipticity (Flattening)            0.0000        0.00335    0.000     
Mean density (kg/m3)                5427          5514       0.984       
Surface gravity (eq.) (m/s2)        3.70          9.80       0.378     
Surface acceleration (eq.) (m/s2)   3.70          9.78       0.378     
Escape velocity (km/s)              4.3          11.2        0.384     
GM (x 106 km3/s2)                   0.02203       0.3986     0.0553  
Bond albedo                         0.068         0.306      0.222
Visual geometric albedo             0.142         0.367      0.387    
Visual magnitude V(1,0)            -0.42         -3.86         -  
Solar irradiance (W/m2)             9126.6        1367.6     6.673     
Black-body temperature (K)           440.1         254.3     1.731
Moment of inertia (I/MR2)           0.35          0.3308     1.058      
J2 (x 10-6)                          50.3        1082.63     0.055
Number of natural satellites           0             1
Planetary ring system                 No            No

Orbital parameters

                                   Mercury        Earth      Ratio (Mercury/Earth)
Semimajor axis (106 km)             57.91        149.60       0.387     
Sidereal orbit period (days)        87.969       365.256      0.241
Tropical orbit period (days)        87.968       365.242      0.241 
Perihelion (106 km)                 46.00        147.09       0.313 
Aphelion (106 km)                   69.82        152.10       0.459
Synodic period (days)              115.88          -            -     
Mean orbital velocity (km/s)        47.36         29.78       1.590     
Max. orbital velocity (km/s)        58.98         30.29       1.947
Min. orbital velocity (km/s)        38.86         29.29       1.327
Orbit inclination (deg)              7.00          0.00         -   
Orbit eccentricity                   0.2056        0.0167    12.311    
Sidereal rotation period (hrs)    1407.6          23.9345    58.785      
Length of day (hrs)               4222.6          24.0000   175.942
Obliquity to orbit (deg)             0.034        23.44       0.001

Mercury Observational Parameters

Discoverer:      Unknown
Discovery Date:  Prehistoric

Distance from Earth
        Minimum (106 km)            77.3
        Maximum (106 km)           221.9
Apparent diameter from Earth
        Maximum (seconds of arc)    13.
        Minimum (seconds of arc)     4.5
Maximum visual magnitude            -1.9      
Mean values at inferior conjunction with Earth
        Distance from Earth (106 km)         91.70    
        Apparent diameter (seconds of arc)   11.0

Mercury Mean Orbital Elements (J2000)

Semimajor axis (AU)                  0.38709893  
Orbital eccentricity                 0.20563069   
Orbital inclination (deg)            7.00487    
Longitude of ascending node (deg)   48.33167     
Longitude of perihelion (deg)       77.45645  
Mean Longitude (deg)               252.25084

North Pole of Rotation

Right Ascension: 281.010 - 0.033T
Declination    :  61.416 - 0.005T
Reference Date : 12:00 UT 1 Jan 2000 (JD 2451545.0)
T = Julian centuries from reference date

Mercurian Magnetosphere

Dipole field strength: 0.0033 gauss-Rh3
Dipole tilt to rotational axis: 169 degrees
Longitude of tilt: 285 degrees (from Mercury I flyby)
                   115 degrees (from Mercury III flyby)

Note: Rh denotes Mercurian radii, 2,439 km

Mercury Atmosphere (Exosphere)

Surface pressure: ~10-15 bar (0.001 picobar)  
Average temperature: 440 K (167 C) (590-725 K, sunward side)
Total mass of atmosphere: <~1000 kg

Atmospheric composition: 42% Oxygen (O2), 29% Sodium (Na), 
22% Hydrogen (H2), 6% Helium (He), 0.5% Potassium (K),
possible trace amounts of Argon (Ar), Carbon Dioxide (CO2), 
Water (H2O), Nitrogen (N2), Xenon (Xe), Krypton (Kr), 
Neon (Ne), Calcium (Ca and Ca+), Magnesium (Mg)

(The atmosphere of Mercury is essentially a vacuum. Compositional 
values are variable and not well constrained, values from "Mercury",  
Vilas, Chapman, and Matthews, eds., University of Arizona Press, 1988)

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