Mercury

The most fascinating thing about mercury is it's craters. Some say that there was a planet between Mars and Jupiter that exploded and the rocks from that planet fell on mercury and created the craters. Mercury is small, in fact it is the smallest planet because Pluto is known as a dwarf planet. Mercury is just the same size as our moon. Mercury is the closest planet to the sun. So you are wondering, if Mercury is the closest planet to the sun it never gets cold there. Well actually it gets cold on Mercury when it is night time but its not the hottest planet, Venus is. Why? You ask. Because Venus' atmosphere is much thinner than Mercury. Isn't that amazing?

 Why is Mercury so cold at night even though it is right next to the sun?
 Mercury is cold at night even though it is right next to the sun because Mercury's atmosphere is thinner than ours. An atmosphere covers the planet and holds the heat inside it so it would be warm at night.

Why is Mercury's sky always look dark?
Mercury's sky always looks dark because the air of the atmosphere doesn't scatter the light waves from the sun.

This is the picture taken by MESSENGER. An unmanned spaceship that NASA  built to go close to Mercury.