(The second value represents the quantity as a fraction of the terrestrial value.)
Mass 330.2e21 kg 0.0553 GM 22.03e3 km3/s2 0.0553 Equatorial radius 2440 km 0.383 Polar radius 2440 km 0.384 Flattening 0.0 0.000 Mean density 5427 kg/m3 0.983 Moment of inertia coefficient 0.33 0.998 J2 60e-6 0.055 Surface gravity (equator) 3.70 m/s2 0.378 Escape velocity 4.3 km/s 0.384
Semimajor axis 57.9e6 km 0.387 Sidereal period 87.969 d 0.241 Tropical period 87.968 d 0.241 Eccentricity 0.2056 12.311 Inclination 7.005 deg Synodic period 115.88 d Mean orbital velocity 47.89 km/s 1.608
Bond albedo 0.056 0.145 Visual geometric albedo 0.11 0.300 Visual magnitude V(1,0) -0.42 Solar irradiance 3566 W/m2 2.584 Black-body temperature 442.5 K 1.789
Epoch 1994.0 North pole (RA and Dec) 280.99 deg / 61.44 deg Obliquity 0.0 deg Argument of prime meridian 191.04 deg at epoch Sidereal rotation rate 6.1385025 deg/d Sidereal rotation period 58.646 d
Dipole strength 0.0033 gauss-Rm3
Dipole tilt to spin axis 169 deg
Longitude of tilt 285 deg (from Mercury I flyby)
115 deg (from Mercury III flyby)
Note: Rm denotes Mercurian radii, 2,439 km
Surface pressure ~e-15 bar Average temperature 440 K (590-725 K, sunward side) Composition: Helium (He) 98% Hydrogen (H2) 2%
Epoch JD 2449360.5 Mean distance 0.3871 AU Eccentricity 0.2056 Inclination 7.0053 deg Longitude of ascending node 48.34 deg Longitude of perihelion 77.45 deg Mean longitude at epoch 312.54 deg