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In Roman mythology, Mercury was the messenger god. When the ancients
discovered the planet Mercury, they noticed that it moved quickly across
the night skies, unlike the stars. It looked to them as if the planet was
hurrying to deliver messages to the gods in the night sky. The planet Mercury is the closest to the Sun, and because of this, it is also the fastest planet. Now that Pluto has been "demoted" out of the ranks of the major planets, Mercury is the smallest planet as well. Mercury's average orbital velocity is about 30 miles per second. In comparison, the orbital velocity of the Earth is 18.5 miles per second. Mercury completes an orbit around the Sun (its "year") in just 88 days. It is important to realize that those are "Earth days", the ones we're used to here on the Earth. A rotation around its axis, takes 59 days to complete. Another interesting fact about Mercury's days, is that, due to the fact that its orbital period ("year") is about 50% longer than its rotational period ("day"), the time between on sunrise on Mercury and the next is 176 days! There is very little air on Mercury. What little there is is made up of oxygen (42%), sodium (29%), hydrogen (22%), helium (6%), potassium (0.5%), with the rest being vatious other particles. This lack of an atmosphere means that the side facing the Sun gets very hot, and the side facing away gets really cold. While the average temperature on Mercury is 333 degrees Fahrenheit, in the sun the temperature can reach 845 degrees F, while on the dark side, the temperature can drop to around -300 degrees F. Mercury's surface is rocky and littered with craters. Its core is made up of mostly iron. Facts about Mercury:
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