Mercury is the smallest and innermost planet in the Solar System. Its orbit around the Sun is the shortest of all the planets in the Solar System, and it has no known natural satellites. Mercury is similar in appearance to the Moon, but with one-third the albedo of lunar surface.
It was named after Roman deity Mercury, messenger of gods.
Mercury orbits around the Sun once every 87.969 Earth days, completing three rotations about its axis for every two orbits. The axial tilt of Mercury’s pole has an unusually large obliquity of 2°28′31″ (about 176°), which gives it seasons more extreme than any other planet except Venus. Because mercury orbits so close to sun, it can only be seen near sunset or sunrise, making it a morning star or evening star. However, transits of mercury across the face of sun are among rarest planetary orbital phenomena that occur just 13 times per century on average, next only to solar eclipses in rarity.
Mercury’s surface is heavily cratered and similar in appearance to Earth’s Moon, indicating that it has been geologically inactive for billions of years. Due to its small size and rapid rotation, Mercury has a weak induced magnetic field about 0.1% as strong as Earth’s.
The planet appears to have cooled completely since forming billion years ago. It craters range in diameter from small bowl-shaped depressions to multi-ringed impact basins several hundred kilometers across. They appear to have mostly formed as a result of asteroid impacts during late heavy bombardment period 4 billion years ago.. There are also some evidence for volcanism on Mercury,, although interpretations remain controversial because data from Mariner 10 mission suggest that surface temperature may not have been high enough for significant outgassing event occurred since formation time.
At present there are no plans for another dedicated mission to Mercury, although ESA and JAXA proposed BepiColombo mission which will include two separate orbiters ,one European(MOSIF) and one Japanese(MPO),and will study different aspects of planet including interior structure, composition and environment .BepiColombo is scheduled for launch in 2018.