How does Mercury compare to Earth?
Mercury is much smaller than Earth. It’s actually a lot closer to the size of Earth’s moon. It has a shorter year, but a much longer day. There is no air to breath and the temperature changes wildly each day (even though it’s a really long day!). Mercury is similar in that it has a hard rocky surface like Earth’s. You could walk around on Mercury if you had a space suit and could take the extreme temperatures. How do we know about Mercury? There is evidence that the planet Mercury has been known since 3000 BC by civilizations such as the Sumerians and Babylonians. Galileo was the first to observe Mercury by telescope in the early 1600’s. Several other astronomers since then have added to our knowledge about the planet. Since Mercury is close to the Sun, it is very difficult to send a space craft to explore the planet. The gravity from the sun is constantly pulling on the space craft causing the ship to need lots of fuel in order to stop or slow down at Mercury. There have been two spac
