The closest planet to the sun is Mercury. The surface has plenty of craters. So, visually it looks like the Moon. Its mean
distance from the sun is approximately 5.8 crore km. Mercury revolves about the sun in a period of 88 days. Radar
observations of the planet show that its period of rotation is 58.7 days, or two-thirds of its period of revolution. The
planet, therefore, rotates one and a half times during each revolution. Due to Mercury's rotation and elongated elliptical
orbit, the Sun appears to rise briefly, set, and rise again before it travels westward across the sky. At sunset,
the Sun appears to set, rise again briefly, and then set again. In Mercury, the day is longer than the year!
In 1974 and 75, the spacecraft Mariner 10 made 3 flybys of Mercury. It took several pictures of the planet from a distance of 327 kms.
The next mission to Mercury, is MESSENGER Spacecraft. It was launched on 3 August 2004. It will go near the planet in the
year 2008 and send detailed information on the planet till 2012.
Mercury is a small planet, we can accommodate about 18 Mercurys inside the Earthís volume.. It is smaller than any other
planet except Pluto. Mercury has no substantial atmosphere. These factors contribute to the fact that the surface of Mercury
has the greatest temperature range of any planet or natural satellite in our solar system. The surface temperature on the
side of Mercury closest to the Sun reaches 427 degrees Celsius, a temperature hot enough to melt tin. On the side facing away
from the Sun, or the night side, the temperature drops to -183 degrees Celsius. Scientists have detected a magnetic field
surrounding Mercury, though it is not as strong as the field around the Earth. Mercury's field is due to an iron-bearing core
of Mercury .
Sunís massive gravitational force pulled almost all its atmosphere. So its atmosphere is very thin and is composed of helium and sodium. Mercury does not have any naturally occurring satellites.
It moves within the orbit of the Earth, because of this, as viewed from Earth, the Mercury never moves beyond 28 degrees.
Consequently, Mercury is visible to us only just before dawn or just after sunset. Also it shows waxing and waning phases
like the Moon.