By Konstantin Kakaes WASHINGTON — About midafternoon Friday
(Eastern time), a 160-foot asteroid known as 2012 DA14 will whip
by the Earth, 17,000 miles (27,000 kilometers) above the Earth's
surface. The asteroid poses no danger to anyone — its trajectory
is well known, and it will miss the Earth. But it "poses no
danger" in the same way that a gun fired a half-inch above your
head does. If you were absolutely certain of the trajectory of
the bullet and knew that it wouldn't hurt anyone else nearby,
and there was nothing you could to stop it anyway, you could be
comfortable in the knowledge that it would not affect you at
all. But it doesn't make much sense to ignore the shot entirely.
Impacts of large asteroids on Earth are rare. Asteroids the size
of Friday's would cause only localized damage. The orbits of
larger objects are better known, and so imminent danger of mass
extinction is low. It is unlikely that astronomers will soon
discover a "potentially hazardous asteroid" (PHA) high on what
astronomers have