Summary:
- Mercury is the smallest planet with no moon.
- It is also the planet closest to the Sun.
- The surface of Mercury is covered with craters, like Earth’s Moon.
- Mercury is extremely hot and has a liquid metal core.
- Scientists think that there may be a small amount of water, in the form of ice, at the planet's poles.
- Mercury has a very short year, but it also has very long days.
- It rotates slowly on its axis, turning exactly three times for every two times it orbits the sun.