Mercury is a very small planet, with a surface that is exposed directly to space. This is because the planet has practically no
atmosphere. Normally, no atmosphere would mean very cold, but it is very hot on Mercury. Why?
The surface of Mercury looks much like Earth's moon. ... On its dark side, Mercury gets very cold because it has almost no atmosphere to hold in heat and keep the surface warm. The temperature can drop down to minus 300 degrees Fahrenheit. Sunlight never reaches into the bottoms of some craters near Mercury's poles.
