Asteroid Chicxulub which is 9.6 kilometers wide is believed to have hit the earth 66 million years ago causing 75% of life on earth to be destroyed leading to the extinction of the dinosaurs. Since then in various works of fiction, the human species is also believed to be extinct if an asteroid the size of Chicxulub hits the earth again.
Therefore scientists from NASA and ESA track asteroids in space with those located within 45 million kilometers categorized as near-Earth asteroids. Now they report 30,039 near-Earth asteroids have been successfully tracked so far. Of this number, 1425 have a probability of hitting the earth within a period of 100 years.
Astronomers have detected asteroids since the first one, Ceres, was discovered in 1801. Then the first near-Earth asteroid was discovered in 1898. Any asteroid with a width exceeding 140 meters has the potential to destroy a small town.
Because there is a small probability that an asteroid will hit the earth in the future, NASA has done DART recently which successfully deflects the course of the asteroid hit as the earth's defense system.