All clear for asteroid fly-by

Astronomers continued to observe an asteroid Friday that they said made the closest recorded brush with Earth.

The 30-metre-diameter rock passed harmlessly about 43,000 kilometres above the southern Atlantic Ocean on Thursday. Asteroid 2004 FH was expected to be beyond the moon's orbit by Friday.

Steven Chesley, an astronomer with the near-Earth object program at NASA's Jet Propulsion Laboratory, said it was the closest recorded encounter.

If the asteroid had hit Earth, it would likely have broken up in the atmosphere, producing shock waves strong enough to break windows on the ground.

Chesley estimated there's a one-in-a-million chance Asteroid 2004 FH could hit in the future. Scientists expect to eliminate the possibility as they learn more about its orbit.

It won't hurtle by Earth again until 2044, when it should pass within 1.5 million kilometres.

Brushes with asteroids of this size are believed to occur about once every two years on average, but most pass by undetected, Chesley added.