Lumps of rock that orbit the Sun are called asteroids. They are also known as minor planets. Most asteroids are in the asteroid belt, which lies between Mars and Jupiter. Some distant asteroids are made of ice and orbit the Sun beyond Neptune. There are more than one million asteroids bigger than one km across. More than 200 asteroids are more than 100 km across. A few asteroids come near Earth. They are called Near Earth Objects. The first asteroid to be discovered was Ceres in 1801. It was detected by Giuseppi Piazzi, one of the Celestial Police, whose mission was to find a ‘missing’ planet. Ceres is the biggest asteroid with 940 km across and 0.0002 percent of the Earth’s mass. Small asteroids are burnt up by the Earth’s atmosphere every day. The chances of a big one colliding with us and destroying the Earth are remote. Every 50 million years, the Earth is hit by an asteroid measuring more than 10 km across.