E ven though Mercury was visited by just one explorer spacecraft, Mariner 10, we received a great deal of data about its make-up and history. This probe was launched on November 3, 1973 and made three passes of the planet in a two year period between 1973 and 1975. You can't find a completely accurate picture of this planet because Mariner 10 only mapped out about half of the planets surface. Scientists can't get accurate pictures of the planet because it is located so close to the sun.

T he Mariner 10 satellite also found a magnetic field that surrounds the planet which is about 1% as strong as the one on Earth. Scientists assumption that Mercury is very dense turned out to be true. It's density is comparable with that of Earth which is about 5.5 g/cm³. It was also found to be made up of 60 - 70 percent by weight metal, and 30 percent by weight silicate. The core radius covers about 75 percent of the planet and accounts for 42 percent of the total volume.

S cientists used the different phases of Mercury in order to calculate the planets rotation period. In 1965, using radar, Pennengill and Dyce deduced that the planets rotation period must be 59.5 days. Then later in 1971 Goldstein, also using radar, narrowed down the rotation period to 58.9 days. Then finally, the accurate rotation period was discovered when the Mariner 10 space probe studied Mercury. It was found to be 58.6462 days exactly.

M ercury's orbit around the Sun is extremely elliptic, at aphelion it is about 70 million kilometers from the Sun and at perihelion its only about 46 million. Before Einstein came up with his Theory of relativity, scientists could not explain Mercury's orbital parameters. Previously, scientists used Newtonian mechanics to figure out the orbit of a planet. As scientists observed Mercury the inconsistency between predicted values and the actual values of the orbit bewildered the scientists. Some even believed that another near by planet might exist (some called it Vulcan) that was altering Mercury's course. Mercury was one of the key examples that helped to prove the accuracy of Einstein's theory. The temperature variations on the planet were found to be the most extreme of any celestial body in our solar system. They range from a high of 450 degrees Celsius to a low of -160 degrees Celsius. The only planet that is hotter than mercury is Venus but its temperature is a lot more stable.