... One planetary astronomer has likened our solar system to a "cosmic shooting gallery,'' with asteroids and comets whizzing through space, occasionally zooming perilously close to Earth. ... What about the comet that's supposed to hit the Earth in 130 years? ... Most scientists now agree that, 65 million years ago, a six-mile-wide asteroid hurtling through space at 15 kilometers/second (9 miles/second), a hundred times faster than a speeding bullet, slammed into the Earth. ...