Mercury is the smallest and closest to the Sun of the eight planets in the Solar System, with an orbital period of about 88 Earth days. Seen from Earth, it appears to move around its orbit in about 116 days, which is much fster than any other planet in the Solar System. It has no known natural satellites. The planet is named after the Roman deity Mercury, the messenger to the gods.
Because it has almost no atmosphere to retain heat, Mercury's surface experiences the greatest temperature variation of the planets in the Solar System, ranging from 100 K(-173 ºC and -280 ºC) at night to 700 K (427 ºC; 800 ºF) during the day at some equatorial regions. The poles are constantly below 180 K (-93 ºC; -136 ºF).
Mercury's axis has the smallest tilt of any of the Solar System's planets (about 1/30 of a degree), but ithas the largest orbital eccentricity. At aphelion, Mercury is about 1,5 times as far from the Sun as it is at perihelion. Mercury's surface is heavily cratered and similar in appearance to the Moon, indicating that it has been geologically inactive for billions of years.
