Asteroids
Asteroids are pieces of metal and rock which are left over from when the Solar System was formed. They form a belt between Mars and Jupiter. If an asteroid strayed from the belt and collided with Earth we may not survive the collision. It has happened before when the Dinosaurs ruled.
Asteroids are like comets but are larger and are made up of rock and metals much like the inner planets.
Even asteroids can have moons like Ida and its moon Dactyl.
No human has ever set foot on an asteroid. It's not likely we will until we devolop space ships that can fly very fast, otherwise it may take over a year to get to the belt.
Ceres is one of the largest asteroids in the Solar System. It's just about 1,000 km across. That is a quarter the size of our Moon. If all the asteroids could overcome the gravity of the Sun and Jupiter they could form a planet the size of our Moon.
In the near future an expedition might be launched to mine an asteroid. This is because they may contain valuble minerals.
