Solar System: Planets: Mercury

Mercury is the closest planet to the Sun in the Solar System. Some basic facts about Mercury:

• Diameter of 4880 km
• Density of about 5400 kg/cubic meter
• Average distance from the Sun is 57.9 mil. km (0.39 AU), aphelion 70 mil. km, perihelion 46 mil. km.
• Orbiting time 87.97 days
• Rotational period of 38.65 days
• No rotational axis tilt, thus no seasons
• Mass is about 5.5% that of the Earth
• No atmosphere
• Temperature variations from 700 degrees Kelvin at noon to 100 degrees Kelvin at night

Mercury, due to its very small distance from the Sun, has entered a 3:2 spin-orbit coupling with the Sun. Mercury's surface is very heavily cratered. About 45% of its surface was photographed in 1974-1975 by the Mariner-10 mission.

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