Mercury Fact Sheet

Mercury/Earth Comparison

Bulk parameters

                                   Mercury        Earth      Ratio (Mercury/Earth)
Mass (1024 kg)                      0.3302        5.9736     0.0553
Volume (1010 km3)                   6.085       108.321      0.0562
Equatorial radius (km)	            2440          6378       0.383
Polar radius (km)                   2440          6356       0.384
Volumetric mean radius (km)         2440          6371       0.383
Ellipticity                         0.0000        0.0034     0.000
Mean density (kg/m3)                5427          5520       0.983
Surface gravity (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                         0.056         0.385      0.145
Visual geometric albedo             0.11          0.367      0.300
Visual magnitude V(1,0)            -0.42         -3.86         -
Solar irradiance (W/m2)             9214          1380       6.677
Black-body temperature (K)           442.5         247.3     2.531
Moment of inertia (I/MR2)           0.33          0.3308     0.998
J2 (x 10-6)                          60.         1082.63     0.055

Orbital parameters

                                   Mercury        Earth      Ratio (Mercury/Earth)
Semimajor axis (106 km)             57.9         149.6        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)                 46.0         147.1        0.313
Aphelion (106 km)                   69.8         152.1        0.459
Synodic period (days)              115.88          -            -
Mean orbital velocity (km/s)        47.87         29.79       1.607
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
Obliquity to orbit (deg)            ~0.1          23.45       0.004     

Mercury Observational Parameters

Discoverer:      Unknown
Discovery Date:  Prehistoric

Apparent diameter from Earth
        Maximum (seconds of arc)    13.
        Minimum (seconds of arc)     4.5
Distance from Earth
        Minimum (106 km)            77.3
        Maximum (106 km)           221.9
Apparent magnitude near opposition  -1.9      

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 

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

Surface Pressure: ~10-15 bar (0.001 picobar)
Average temperature: 440 K (590-725 K, sunward side)

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)

(Compositional values not well constrained, values from "Mercury" Vilas,
Chapman, and Matthews, eds., University of Arizona Press, 1988)

NASA Official: J. H. King, joseph.h.king@gsfc.nasa.gov
Last Updated: 27 November 1998, DRW