Mercury — The Speedy Planet
MERCURY is the SMALLEST planet in our solar system and the CLOSEST to the sun. It's named after the speedy Roman messenger god — because Mercury moves around the sun faster than any other planet. One year on Mercury (one trip around the sun) is just 88 Earth days!
Mercury is a rocky planet with NO atmosphere to protect it. That makes the temperatures EXTREME — over 800°F (430°C) on the sunny side, and −290°F (−180°C) on the dark side. The biggest swing of any planet. Without an atmosphere, there's no wind, no clouds, no weather — and craters from old asteroid impacts stick around for billions of years.
Why does Mercury have such big temperature changes between its day and night sides?
Mercury is hard to see from Earth because it's usually close to the sun in the sky. The best times to spot it are just after sunset or just before sunrise. It looks like a bright dot, never far from the horizon. NASA's Messenger spacecraft (2011-2015) gave us our best maps of its surface, including ice in shadowed craters at the poles!
Mercury Math
One Mercury year = 88 Earth days. If you're 10 Earth-years old, how many Mercury years old are you? (Hint: how many 88-day periods are in 3,650 days?)
Mercury reminds us that planets are EXTREME places. Tiny, fast, hot, cold — all at once. Our home Earth, with its protective atmosphere, is a rare gem.
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