Mean orbital velocity per second: 29.7 miles (47.9 km)
Inclination of axis: 0░
Orbital eccentricity: 0.206
Orbital inclination: 7 00'
Diameter at equator: 3,033 miles
4,879 km
0.38 x Earth's diameter
Oblateness: 0
Escape velocity per second: 2.6 miles (4.3 km)
Mean surface temperature: 662 F / 350 C / 623 K (day)
-274 F / -170 C / 103 K (night)
Mass: 3.30 x 10^23 kg
(Earth = 1): 0.055
Volume (Earth =1): 0.056
Density (water = 1): 5.43 g/cm^2
Surface gravity: 2.78m/s^2
(Earth = 1): 0.38
Albedo: 0.1
Number of known satellites: 0
Maximum apparent diameter as seen from Earth (seconds of arc): 12".9
Mean diameter of Sun as seen from the planet: 1 22' 40"
Planet composition
Mercury's high mean density (5.5 grams/cc as compared to 3.34 grams/cc for the Moon) prompts researchers to speculate that the planet has a thin mantle and a relatively large iron core approximately 3,600 km (2,200 miles) across. With a core composition of 65-70 percent iron (by weight), Mercury is twice as rich in iron as any other planet in the solar system.
Core=3,600 km in diameter
Mantle=275 km thick
Crust = 415 km thick
Atmosphere
The planet has only a trace atmosphere, composed mainly of argon, neon, and helium, and its surface pressure is one trillionth of the pressure on Earth.
Mercury boasts the largest surface temperature variance in the solar system, ranging from -298░ F / -183░ C / 90░ K on the dark side to 872░ F / 467░ C / 740░ K on the light side.
Magnetic fields and gravity
Mercury's weak magnetic field (about 1/100 of Earth's) is closely-aligned with planet's axis of rotation. The surface gravity on Mercury is 0.377.
Orbit and rotation
Obit has a mean radius of only 36 million miles (58 million km), which means it's usually too close to the sun to be seen. Mercury spins only three times on its axis in the course of two of its years.
With the exception of Pluto, Mercury has the most eccentric orbit of all the planets.
Topography
Mercury is difficult to observe from Earth because it's never seen against a dark background (the best observation times being near sunrise and sunset, when the same feature are always pointed toward Earth). Most of our knowledge of Mercury is a result of the 1974 Mariner 10 flyby.
Craters are the main topographical feature on the planet. Most were created approximately 4 to 4.5 million years ago and range from 100m to 1,000 km in diameter. Mercury also has plains, which researchers believe were formed later in Mercury's evolution. Other features include scarps and troughs, which are probably the result of tectonic activity.
The planet's northwest quadrant is dominated by the Caloris Basin (1,300 km in diameter), the largest structural feature on Mercury. The northeast quadrant contains a smooth plain (Borealis Planitia) and a large lava-flooded basin, 310 km in diameter. There are also several prominent ray craters, including Rodin; a double ring basin surrounded by other major craters. The southwest quadrant consists mainly of inter-crater plains. The largest crater in the region is Beethoven (625 km wide; the second-largest known crater on Mercury). The southeast quadrant is the most heavily cratered and probably the oldest. This region also hosts three relatively young ray craters (Coply, Snorri, and Kuiper) and eight of 16 named scarps on the planet.
Moons and/or rings
There are no known moons or rings associated with Mercury.
Mythology
This planet was known to the Egyptians and Greeks, who named it after Hermes (Mercury), the messenger of the Gods and deity of science, eloquence, and cunning. In ancient astrology, a child born under Mercury loved learning, travel, and art. Wednesday was dedicated to Mercury, which was known to influence the kidneys of the human body.
Discovery and exploration
The first Mercurian observer is believed to be Johannes Hevelius in the 17th century. First maps of Mercury were created by G. V Schiaparelli beginning in 1821 (in Milan). The only exploratory probe to visit Mercury was Mariner 10. Its flyby in March 1974 provided most of what we know about Mercury today.
[Rick: No data found on belief in early life forms.]