The planet Mercury is the smallest planet in our solar system, and the one that is closest to the sun. This proximity to the sun has made it difficult to study the planet. The closest look that we have ever had was in 1974 and 1975 when the unmanned Mariner 10 was sent to map the surface of Mercury. Only about 40% to 45% of the surface was actually mapped.
Mercury resembles our moon in appearance as it is heavily cratered. There is an atmosphere of sorts on Mercury but not one that would sustain life as we know it. The atmosphere is very unstable and is made up of hydrogen, helium, oxygen, sodium, calcium and potassium.
Records of studies made of Mercury date back to 300 BC. The name "Mercury" was given to the planet by the Romans after the god Mercurius. Chinese, Korean, Japanese, and Vietnamese cultures refer to Mercury as the water star based on the Five Elements. Other cultures have called the planet by other names. The Babylonians, for example, called the planet Nabu or Nebu after the messenger to the Gods in their mythology.
The temperature on Mercury varies. The average temperature is 179° C, but the extremes are a low of -183 °C to a high of 427° C. Sunlight on Mercury is six and a half times stronger than it is on Earth.
There is evidence that water does exist on Mercury despite the extreme temperature variations. The bottoms of some of the deepest craters near the poles are never exposed to direct sunlight. Temperatures in these areas remain far lower than the global average, so it is possible for ice to exist.
