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) 6.083 108.321 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 5515 0.984
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 0.119 0.306 0.389
Visual geometric albedo 0.106 0.367 0.289
Visual magnitude V(1,0) -0.42 -3.86 -
Solar irradiance (W/m2) 9126.6 1367.6 6.673
Black-body temperature (K) 442.5 254.3 1.740
Moment of inertia (I/MR2) 0.33 0.3308 0.998
J2 (x 10-6) 60. 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) 47.87 29.78 1.607
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) 0.01 23.45 0.0004
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: 281.01 - 0.003T Declination : 61.45 - 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
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) (The atmosphere of Mercury is essentially a vacuum. Compositional values are not well constrained, values from "Mercury", Vilas, Chapman, and Matthews, eds., University of Arizona Press, 1988)