Mercury

Mercury is the smallest of the planets and is closest to the Sun. Due to its closeness to the Sun, it circles the sun faster than all the other planets, that is why the ancient Romans named it after their swift-footed messenger god. Mercury has the longest period of rotation and shortest ‘year’, taking only 88 days to orbit the Sun.

Mercury has almost no atmosphere. As it is very small in size, its gravity is too weak to hold down a normal atmosphere. However, around the planet, there is a very thin atmosphere, which is constantly being ‘blown away’ into the space by the pressure of sunlight and by the solar wind. Gases are also constantly being added to Mercury's atmosphere. The atmosphere of Mercury contains small amounts of hydrogen, helium, and oxygen.

In size, it is slightly larger than Earth's moon and like the moon, the planet is also pockmarked with craters. Mercury's interior is dominated by a large iron core, which is denser than that of any other major planet in the Solar System.

Mercury records a very high temperature, as it is very near the Sun. Until recently it was thought that Mercury completed one rotation as well as one revolution in 88 days and that is why one side of Mercury always faced the Sun. So, the side facing the Sun had extremely high temperatures and the side away from the Sun had extremely low temperatures. However, radar observations show that the planet complete one rotation in about 58 days. This means that Mercury has a solar day equivalent to 58 earth days. So, any spot on Mercury faces the ferocious heat of the Sun continuously for 58 days. Thus the sunlit side records more than 400ºC, while the dark side may have a temperature of 180º below the freezing point.

There is no water in Mercury. The planet is very hot, and its atmospheric mantle is so thin that it can be safely concluded that, Mercury is airless too. It is therefore obvious that, no life can exist on Mercury.

Mercury can be seen in the sky in the early evenings of March and April, as the Sun begins to set and just before the sunrise in September and October.