Mercury is the closest planet to the Sun. Mercury has a diameter of about 4,900 km. It is a small planet, while revolving around the sun, its distance from the sun changes. It has been found that the maximum distance of Mercury is double its minimum distance from the sun. It has no sub-planets.
It takes about 88 days to complete one revolution around the Sun. This is the time it takes to complete one rotation about its axis. Hence, it always shows the same face towards the sun. The side of Mercury facing the Sun has a temperature of about 400oC, but the opposite face perpetually in the dark has temperature of -200oC. This planet has low gravity which caused the planet to lose its atmosphere.
A spacecraft known as Mariner 10 has taken its photographs on March 29, 1974. The dominant features are meteoritic craters which in the absence of atmospheric erosion have retained many of their impact features. The large craters display central peaks and rings just like lunar craters. The biggest crater is Calorios Basin 1300 km across terrin appears bright while the smooth plains appear dark suggesting basaltic composition.
Mercury rises a little earlier than the sunrise and sets a little after sunset. Though it is a bright planet, it cannot be studied much because of the small duration during which it can be seen.
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