Introduction
Mercury is the first planet in our solar system. From the Earth, Mercury is
seen as a slightly pinkish disk or at times as a
crescent.
It has a diameter 0.38 times that of Earth (= 4,880 km), a mass of 0.055 that of
the Earth's and a density of 5.43g/cm3. It rotates
once on its axis in 58.65 days.
Atmosphere
Mecury has a surface temperature that varies the most, ranging from 90 K to
700 K. It has no permanent atmosphere since the atmosphere consists of air
molecules that move fairly fast. However, traces of hydrogen and helium gases
could be detected.
These gases are captured from the solar wind
and are able to remain on the planet for a few weeks before escaping into
interplanetary space. Earth-bound astronomers have also found an extremely
tenuous envelope of sodium and potassium around Mercury.
Terrain
The
surface of Mecury resembles that of the Moon most. There are cratered highlands
such as those in the Discovery quadrangle, the Bach area and the Shakespeare
quadrangle, but few maria. Thus it resemble the
Moon's far side and the cratered highlands.
Special Features
Mercury has no permanent atmosphere as compared to other terrestrial planets. This is due to the lower escape velocity of Mercury.