According to the passage, how many moons does Mercury have?

Mercury is the smallest planet in our solar system, only a little bigger than our Moon, and the closest planet to the Sun. From its surface, the Sun would look about three times larger and seven times brighter than it does from the Earth.

You might expect such a planet to be the hottest of all. It is not; Venus is hotter. But Mercury is certainly a place of extremes. During the day its surface can reach about 430 degrees Celsius, hot enough to melt some metals. At night it can fall to about 180 degrees below zero.

The reason for this wild swing is partly that Mercury has almost no air. Instead of a proper atmosphere, it has only a very thin layer of atoms, blasted off its surface by the solar wind and by small rocks from space. With no thick blanket of air to hold in heat, the warmth of the day escapes quickly into space once night falls.

Like the Earth, Mercury is a rocky planet with a solid surface, and that surface is covered in craters. It has no moons at all.