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Image courtesy USGS, and NASA

Origin of name
Mercury is named after the Roman messenger god Mercurius because it moves so swiftly across the sky.

Naming convention
Craters: famous artists, musicians, painters and authors.

ESA mission


BepiColombo, an ESA mission in cooperation with Japan, will explore Mercury, the planet closest to the Sun. Europe's space scientists have identified the mission as one of the most challenging long-term planetary projects, largely because Mercury's orbit so close to the Sun makes the planet difficult for a spacecraft to reach and difficult to observe from a distance. Scientists want to study Mercury because of the valuable clues it will provide in understanding how planets form.



Physical Properties


Property Unit Value Earth = 1
Equatorial radius km 2439.7 0.383
Polar radius km 2439.7 0.384
Flattening   0.0000 0.000
Mass  (x1024) kg 0.3302 0.055
Volume  (x1010) km3 6.083 0.056
Mean density kgm-3 5427 0.984
Surface gravity at equator ms-2 3.70 0.378
Escape velocity kms-1 4.3 0.384
Magnetic field at equator  (x10-4) T 0.0033 0.01
Magnetic dipole moment  (x1012) Tm3 ~ 5.54 ~ 0.0007
Tilt of dipole axis ° 14  
Dipole field centre offset from planet centre (equatorial radii)   0.05  


Orbital Parameters


Property Unit Value
Perihelion  (x106) km 46.00
Aphelion  (x106) km 69.82
Mean distance from the Sun  (x106) km 57.91
Mean distance from the Sun AU 0.387
Eccentricity   0.2056
Sidereal orbit period d 87.969
Sidereal rotation period d 58.65
Length of day d 175.94
Orbit inclination to Ecliptic ° 7.00
Mean orbital velocity kms-1 47.87
Maximum orbital velocity kms-1 58.98
Minimum orbital velocity kms-1 38.86
Axial tilt ° 0.01



  • Sidereal orbit period
    The time taken by the planet to complete exactly one orbit around the Sun with respect to the celestial sphere.
  • Sidereal rotation period
    The time in which the planet rotates around its axis exactly 360° with respect to the celestial sphere.
  • Length of a day
    Defined as the time between two successive sunrises over the meridian.
  • Magnetic dipole moment
    Calculated as the ratio of the magnetic field strength at the equator divided by the cube of the equatorial radius.


Last Update: 1 September 2019
27-Sep-2020 03:45 UT

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