Bulk parameters

• Parameter ** Mercury Value ** Earth Value ** 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 ** 9.80 ** 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 ** 0.119 ** 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

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Orbital parameters

• Parameter ** Mercury Value ** Earth Value ** 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

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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

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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

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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

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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)