Facts about planet Mercury

View of planet Mercury

Mercury, named by the Romans after the messenger of the gods, is the closest planet to the Sun, and second smallest planet in the Solar System. It is believed that Mercury resembles very much the Moon (its diameter is almost as twice as the diameter of Earth's only satellite).

Its surface carries the signature of heavy asteroid and meteorite bombardment that took place since its early ages, recognisable by the huge amount of craters of all sizes that dots the surface.

Mercury basically doesn't have any atmosphere, so the 'sky' surrounding it is always black. Differently from Mars and Venus, the planet has a weak magnetic 'dipole' field (like the one on Earth), indicating that it may also have an iron core that is at least partially molten (planetary magnetic fields are generated from the rotation of a conductive molten core and is known as the 'dynamo effect'). The planet's high density indicates that Mercury is composed by 60 to 70 percent of high-density metallic elements, and about 30 percent of silicate.

Some Mercury statistics:

Mercury's Diameter:

4878 km 0.382 Earth diameters
Equatorial radius (km): 2439.7
Polar radius (km): 2439.7
Planetary Mass: 3.3x1023 kg (= 330 000 billions of billions of kg) 0.055 Earth masses
Average Distance from Sun: 57.91 million km 0.387 AU
(=Astronomical Units, each
corresponding
to 150 million km)
Length of Day:
(Sidereal rotation period)
58.6462 Earth days 1407.6 hrs
Length of Year: 87.969 Earth days
Synodic period: 115.88 Earth days The time interval
between similar configurations
in the orbit (e.g. opposition)
of the body and Earth
Eccentricity: 0.205632
Inclination: 7.004986
Mean density: 5427 kg/m3
Average temperature: 500 degrees Celsius (Day)
150 degrees Celsius (Night)
440 K (167ºC)
(590-725 K, sunward side)
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)
Surface Pressure: ~10-15 bar (0.001 picobar)

Last update: 7 December 2007

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