Mercury

Mercury, or Sol I, is the first planet in the Sol System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. It is named after the Roman god Mercurius (Mercury), god of commerce, messenger of the gods, and mediator between gods and mortals, corresponding to the Greek god Hermes (Ἑρμῆς). Like Venus, Mercury orbits the Sun within Earth's orbit as an inferior planet, and its apparent distance from the Sun as viewed from Earth never exceeds 28°. This proximity to the Sun means the planet can only be seen near the western horizon after sunset or the eastern horizon before sunrise, usually in twilight. At this time, it may appear as a bright star-like object, but is more difficult to observe than Venus. From Earth, the planet telescopically displays the complete range of phases, similar to Venus and the Moon, which recurs over its synodic period of approximately 116 days.
Mercury rotates in a way that is unique in the Sol System. It is tidally locked with the Sun in a 3:2 spin–orbit resonance, meaning that relative to the fixed stars, it rotates on its axis exactly three times for every two revolutions it makes around the Sun. As seen from the Sun, in a frame of reference that rotates with the orbital motion, it appears to rotate only once every two Mercurian years. An observer on Mercury would therefore see only one day every two Mercurian years.
Mercury has no permanent population due to its close proximity to the sun, but both the UNF and USSR have mining outposts that are regularly rotated out because of solar radiation.

Mercury

Astrorgraphical Information

System

Sol System

Orbiting

Sol

Orbital Position

First planet

Moon(s)

None

Physical Details

Diameter

4,879 km (3,032 miles)

Gravity

3.7 m/s²

Length of day

4,224 hrs (176 days)

Length of Year

88 days

Atmosphere

None

Surface Temperature

-180°C to 430°C (-290°F to 800°F)