SAN FRANCISCO (Reuters) - About 1,000 asteroids big enough to
cause catastrophic damage if they hit Earth are orbiting relatively
nearby, a NASA survey shows.
In a project known as Spaceguard, the U.S. space agency was
ordered by Congress in 1998 to find 90 percent of objects near
Earth that are 1 km (0.62 of a mile) in diameter or larger.
The survey is now complete, with 93 percent of the objects
accounted for, astronomer Amy Mainzer of NASA's Jet Propulsion
Laboratory in Pasadena, California, said at the American
Geophysical Union conference in San Francisco on Tuesday.
Using NASA's recently retired Wide-field Infrared Survey
Explorer (WISE) telescope, scientists also found about 20,500
smaller asteroids near Earth.
Previous studies estimated there were 36,000 to 100,000 of these
objects, which have a diameter of about 100 meters (110 yards).
"They could still pack quite a punch," Mainzer told Reuters,
adding that "any impact is not a very likely event."
But a major asteroid strike could and has happened.
An asteroid or comet between 5 and 10 km (3.1 and 6.2 miles) in
diameter is believed to have smashed into Earth some 65 million
years ago, triggering global climate changes that led to the
extinction of dinosaurs and other animals.
"We know something that big could wipe out mostly all life on
Earth," Mainzer said.
Scientists are now using archived WISE observations to home in
on potentially hazardous objects whose orbits come within about 4.6
million miles (7.4 million km) of Earth.
So far, there is no plan about what to do if an asteroid was
discovered to be on a collision course with Earth.
(Editing by Jane Sutton and John O'Callaghan)