(c) Anthony K. Grafton 2003

Our Solar System, Part 2: Mercury: Small, Hot, and Fast

Mercury is the second smallest planet in our solar system, but it is the closest planet to the sun. In many ways, Mercury is a planet of extremes.

At its closest approach, Mercury is only 46 million kilometers from the sun. Compare this to the Earth, which is more than 147 million kilometers away from the sun. Because of its nearness to the sun, Mercury gets very hot during the day. In fact, it gets hot enough to melt lead.

With all this heat, one might hope that Mercury has a short day. Unfortunately, that’s not the case. One day on Mercury lasts about 6 months on Earth. At night, the temperatures reach down to other extremes, with average temperatures dipping to a couple of hundred degrees below zero.

Because Mercury is so close to the sun, it has a very short year. One year for a planet is the time it takes that planet to go all the way around the sun. One year on Mercury would last only 88 days on Earth.

Much of what we know about Mercury comes from data recorded by the Mariner 10 probe. This probe was launched by the United States and reached Mercury in 1974. The surface of Mercury was found to very cratered, much like our own Moon. In addition, the Mariner 10 probe showed that Mercury does have a thin atmosphere made mostly of helium.

Because the sun is so bright and Mercury is so near to it, this small planet is not easy to observe, but you can see it with the naked eye if you look at the right time. Next month, look low on the eastern horizon just before sunrise. Mercury will appear as a small, twinkling light. The only other time of the year you can see Mercury easily is in May, just after sunset low in the western sky.