1. Around every year, an asteroid the size of a car hits earth's atmosphere, creates an impressive fireball, and burns before reaching earth's surface.
2. Every 2000 years, a meteoroid as big as a football field hits earth and causes a huge amount of damage.
3. Sometimes an object large enough to threaten earth's civilization come along...but this happens once every few million years.
4. Space rocks smaller than 25metres will probably burn up as they enter the earth's atmosphere and cause little or no damage.
5. If a meteoroid bigger than 25metres, but smaller than a kilometre hits earth, it would cause local damage at the impact zone.
6. Anything larger than one or two kilometres could have worldwide effects. Toutatis is the largest known potentially hazardous asteroid. It measures 5.4 kilometres.
7. However, asteroids in the main belt between Mars and Jupiter can be as big as 940 kilometres and pose no threat to earth.
Is it an asteroid, comet or meteor?
An asteroid is a relatively small, inactive, rocky body that orbits the sun.
Also relatively small, a comet is active at times. It's ices can vaporize in sunlight forming an atmosphere (coma) of dust and gas and, at times, a tail of dust or gas.
A meteoroid is a small particle from a comet or asteroid that orbits the sun.
The light phenomena which results when a meteoroid enters the earth's atmosphere and vaporizes is a meteor or shooting star.
A meteoroid that survives its passage through the earth's atmosphere and lands on earth is called a meteorite.
For more information, visit NASA.
