If any was detected, work would begin on interceptors to deflect a doomsday rock.

SOMEWHERE in space at this moment, hurtling toward Earth at roughly 16 miles a second, is the doomsday rock.

The doomsday rock is an asteroid large enough to severely disrupt life on Earth upon impact, lofting pulverized rock and dust that blocks most sunlight.

The bigger ones would truly be doomsday rocks.

It was caused by a doomsday rock from space that hit the Earth in a fiery collision and carved a 185-mile-wide crater on what is now the northern Yucatan Peninsula.

Evidence soon began to accumulate that the catastrophe was temporally and geographically variable, leading some scientists to dismiss altogether the idea of a doomsday rock and a global pall of dust.

In the plan, ground-based telescopes would scan the heavens to warn of impending danger as work began on interceptors that would deflect a doomsday rock headed for the planet.

Scientists say that "doomsday rocks" a few miles wide might hit once every 10 million years or so, causing mayhem on a planetary scale.

More worrisome are proposals to mount an attack on any doomsday rock that seems headed this way.

The new information will help scientists calculate how often these strikes occur and the odds of "doomsday rocks" hitting the planet.