In 1801, an Italian Astronomer named Guiseppe Piazzi was searching for planets. What he found was a much smaller, unusual object that he named Ceres . Soon other astronomers saw similar objects that shone like faint stars but behaved like planets. We now know of thousands of these objects floating around in space.
Carbonaceous asteroids are the most common.
Scientists are still gathering more information about the origins of these space rocks and why they are there. Trojans, are clusters of asteroids caught in Jupiter's gravity. Some are trapped in front of the giant planet and others are caught in its wake. Near-Earth Asteroids, or Apollo asteroids sometimes come very near the Earth's orbit but, usually stay well away from the sun. Astronomers know of at least 200 large asteroids that have Earth-crossing orbits.