What is the chance of an asteroid hitting Earth and how do astronomers calculate it?
Perry A. Gerakines, an assistant professor in the department of physics at the University of Alabama at Birmingham, explains. We have extensive evidence that Earth has already been hit by asteroids many times throughout history-the most famous (or infamous) example is probably the asteroid or comet that created the Chicxulub crater in the Gulf of Mexico and may have contributed to the extinction of the dinosaurs at the end of the Cretaceous Period 65 million years ago. A more recent but less devastating example, called the Tunguska event, occurred in 1908, when a meteor or comet exploded over the wilderness of Siberia, damaging farmland and leveling trees for miles around. Because most of the earth is covered by oceans, there may also be many small impacts that go unnoticed. There are thousands of small bodies that we call asteroids or meteoroids in orbit around the sun. Many of these objects are called near-Earth asteroids (or NEAs) because they have orbits that repeatedly bring them
