Composite of video images from Mariner 10 after it flew past Mercury in March 1974.

Orbital Elements
Mean distance from Sun57,910,000 km    =    0.3871 astronomical unit
Perihelion distance45,900,000 km=    0.3068 astronomical unit
Aphelion distance69,700,000 km=    0.4659 astronomical unit
Eccentricity of orbit0.2056
Inclination of orbit7.004relative to Earth's orbit
Period of orbit0.2408445 year=    87.96845 days    =    87:23:14:34
Synodic period116 daysrelative to Earth
Mean orbital speed47.88 km/s
Minimum orbital speed38.86 km/s
Maximum orbital speed58.98 km/s
Physical Properties
Diameter4,879.4 km=    0.3825  Earth diameter
Radius2,439.7 km
Mass3.303 x 1023 kg=    0.055271  Earth mass
Mean density5.42 g/cm3
Rotational period58.6462 days=    58:15:30:30    =    2/3 of a Mercury year
Length of day175.9421 days
Inclination of axis0.00relative to the axis of its orbit
Gravity at surface2.78 m/s2=    0.38  Earth gravity
Escape speed4.25 km/sfrom surface
Visual geometric albedo0.10
Visual magnitude (Vo)-1.9maximum, as seen from Earth
Mean surface temperature179C
Minimum surface temperature-173C
Maximum surface temperature    427C
Atmospheric pressure0.0 barsMercury has very little atmosphere
Atmosphere   composition
Helium (He)
Sodium (Na)
Neon (Ne)
Argon (Ar)
Hydrogen (H)

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Jeff Root
September 4, 2003