Mercury is the innermost planet in the Solar System. It orbits the Sun once in about 88 Earth days completing three rotations about its axis for every two orbits.
Mercury is one of four terrestrial planets in the Solar System and is a rocky body like the Earth. It is the smallest planet in the Solar System with an equatorial radius of 2439.7 km.
Mercury's core has a higher iron content than that of any other major planet in the Solar System.
Mercury's surface indicating that it has been geologically inactive for billions of years.
Mercury's axis has the smallest tilt of any of the Solar System's planets, but Mercury's orbital eccentricity is the largest.
Mercury and Venus can each make appearances in Earth's sky both as a morning star and an evening star and at times Mercury can technically be regarded as a very bright object when viewed from Earth.