Image credit: NASA
Mercury is the smallest planet. It is a small, rocky ball in space. You could not live on Mercury. Days are very hot - the surface of Mercury is hot enough to melt some metals! Nights are very, very cold. But if you could go to Mercury, things would seem very strange.
All of Mercury's surface is dry and rocky. There are no seas. There are no rivers or lakes. There are many craters like on our moon.