But what cosmic machinations flung that particular asteroid at Earth at that moment in history?

A new computer simulation suggests that a wobble in the orbit of Mercury may be the root cause of the dinosaur disaster. The speculative work, led by Bruce Runnegar from the University of California at Los Angeles' Center for Astrobiology, was reported this week by New Scientist magazine.

Asteroid experts and paleontologists generally agree that a large space rock hit Earth and brought on the end of the Cretaceous period, along with the downfall of dinosaurs and many other species. Solid evidence exists in the form of a large, mostly submerged crater centered on Mexico's Yucatan Peninsula. The crater is dated to a time when fossil evidence shows a mass die-off of small critters around the world.

Runnegar says changes in Earth's orbit triggered a significant adjustment in Mercury's orbit 65 million years ago, which caused a tug on the asteroid belt, a region of space between Mars and Jupiter that is littered with space rocks. Asteroids in a certain part of the belt would have then had a greater chance of getting knocked out of place, Runnegar and his colleagues claim.

While the shake-up would not have sent a shower of asteroids Earthward, at least one rock might have been dislodged and sent on a course toward Earth, Runnegar said. "It's quite plausible that some of the asteroids were affected," he told the magazine.

Other researchers were skeptical.

"I can't believe that Mercury has an effect on anything in the Solar System," said Mark Bailey, director of the Armagh Observatory in Northern Ireland.

Bailey did not discount the computer modeling itself, but said the link between that and the dinosaurs was tenuous at best.

Runnegar and his colleagues mapped out 250 million years of solar system dynamics, studying in particular the times when each planet was closest to the Sun, a point called perihelion. Because all the planets exert a tug on each other, the period of this perihelion changes slightly over time.