Planet Mercury:
	Mercury is the closest planet to the Sun and the second smallest in the solar system.Mercury speeds around the Sun at an amazing 127,000 miles per hour.Because it is so near the Sun,it can be seen from Earth only with difficulty--low in the dawn or twilight sky close to the Sun. It has a high density ,with about 80 percent of its mass in its huge,iron core. Mercury surface is scarred by thousands of craters and by cliffs that form when the planet young core cooled and shrank,contracting  the surface crust. Mercury has almost no atmosphere because its surface gravity is too weak to hold on to one. Mercury has the surface temperature that ranges from  -180 to +430 Celsius (-290 to +800 fahrenheit) Because Mercury is the closest planet to the Sun ,it must race around the sun faster than any other planet in order to maintain a stable orbit.Mercury there fore has the shortest year of any planet ,taking 88 Earth days to orbit the Sun once,at an average speed of about 48 km per second. Mercury surfaceis covered in craters,most of which formed around 3.5 billions years agowhen the planet was bombared by meteorites. Mercury surface is made up of thousands of craters as well as mountains and lava plains. Mercury's surface look quite similar to that of our moon. Mercury has great extremes of temperature.Where it faces the Sun, it can exceed 752 Fahrenheit (400 Celsius), but during the long nights (lasting about 59 earth days) and with no atmosphere to keep the heat in, temperature can plummet to -274 Fahrenheit (-170 celsius).