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Only fifty percent larger than our moon and the planet closest to the sun, Mercury is 3,026 miles in diameter. It rotates around the sun every 88 days at a distance of 36 million miles away. Since the sun and mercury are so close together the planet is difficult to see from earth. Mercury is a waterless and airless planet scarred by craters of all sizes. The side of Mercury that faces the sun heats up to a temperature of 742 degrees fahrenheit while the dark side of the planet is bitterly cold at a temperature of -360 degrees fahrenheit.

Trying to study Mercury from the earth was so difficult a task that for years astronomers couldn't be sure how long it took the planet to rotate on its axis. With the discovery of radar waves it was learned that the planet rotates in 59 days. Mercury's orbit is much farther out of round that the orbit of the earth. The planet will, at times, come as close as 29 million miles from the sun and at other times be as far away as 43 million miles. Under normal circumstances, Mercury cannot be seen during the day. During a total solar eclipse the planet is visible and occasionally around sunrise or sunset if the conditions are right. Even then the planet will appear blurred due to the slanted path passing through miles of moving air which distorts our perception. When weather is permitting, Mercury will appear as the brightest star in the night sky two or three times a year.

The atmosphere on Mercury is practically non existent with traces of sodium. Particles near the planet are given so much energy by the sun that they easily escape the weak gravity. In 1974 and 1975 NASA's Mariner 10 visited Mercury giving us much of the data we have today on the planet. According to this information Mercury is covered by a fine dust and craters. The craters appear to be much more shallow than those on the moon. Even though the planet gets a great deal of light the surface is fairly dark. It has large lines of cliffs which are called scarps. It is believed these scarps formed when the planet contracted as it cooled shortly after it was formed. This cooling had a wrinkling effect on the surface.

Soon after Mercury formed it is apparent another object collided with the planet stripping off the outer most parts. Smooth plains were found in some regions that were believed to be formed over 3 billion years ago. In the last 100 years Mercury has gone into transit ten times appearing as a small black dot on the sun's disk. No moons were discovered around the planet.