If a one-kilometer asteroid hit the Earth, it would launch massive amount of dirt and debris in the atmosphere. During that time, all that material is blocking the sun from heating the planet. So it gets cooler on the planet and agriculture worldwide is disrupted. The Earth in 'bake mode' More massive asteroids could do worse damage. Such asteroids could cause the atmosphere to heat up and turn much of the planet into a fireball.
Most asteroids remain in the main belt between Mars and Jupiter.
But sometimes collisions can launch large chunks into unstable orbits that move them into what could become collision courses with our planet. Astronomers have identified about 40 percent of the candidate killer space rocks. The computer map model should help them locate many others, said Bottke, a Cornell University astronomer. In some places, asteroids experience traffic jams. In others they have plenty of space, he said.