Mercury is the smallest planet in our solar system. This rocky planet looks a lot like our moon. It has a lot of craters. If you were to visit Mercury during the day, you would need a lot of sunscreen! Mercury is the closest planet to the sun. This means that it is really hot. During the day, it can be 840 degrees Fahrenheit! At night, though, you'd need a lot of blankets! Overnight, it can be as cold as 275 degrees below zero. These hot days and cold nights seem to last forever. That is because this planet rotates very slowly. One day on the planet Mercury would be .....