Mercury is the first planet in the Solar System as well as the smallest. One year on Mercury is about 88 days, which makes it the fastest planet. The surface of Mercury can get as hot as 800 degrees Fahrenheit. This is because of how close it is to the Sun. However, it also has a cold side - the side that doesn't receive sunlight (click here for a better explanation). This side can get as cold as -290 degrees. Despite this, Mercury isn't the hottest planet in the Solar System. That would be Venus - our next planet!
[ADD PHOTOS OF MERCURY'S SURFACE, INTERIOR, MOONS?, AND MORE]