Closest encounter of asteroid

A 100-foot-diameter asteroid passed close but harmlessly by Earth on Thursday, astronomers said. The hurtling rock passed about 26,500 miles above the southern Atlantic Ocean at 2:08 p.m. PST.

It was the closest recorded encounter between Earth and an asteroid, said Steven Chesley, an astronomer at NASA's Jet Propulsion Laboratory who works on a program looking for such objects.

If it had hit Earth it probably would have broken up in the atmosphere. Its shock wave could have been strong enough to break windows on the ground, but nothing like the disastrous climate-changing effects that could result from the impact of an asteroid more than a half-mile in diameter, Chesley said, informs &to=http://www.mercurynews.com' target=_blank>Mercurynews.com

Steven Chesley, an astronomer at NASA in Pasadena, said such encounters probably happened about every two years but are not detected. "There certainly have been closer encounters that we didn’t know about," he added.

Astronomers were continuing to observe the asteroid, 2004 FH, which was expected to be beyond the moon’s orbit by today. It will not come fairly close to Earth again until 2044, when it will be within 930,000 miles.