Last week a small asteroid became the closest-known natural celestial object to pass by the Earth.
By Dr David Whitehouse
BBC News Online science editor
It was found by astronomers at the Lowell Observatory in Arizona, which conducts a sky survey for so-called Near Earth Objects.
It posed no danger but it was close
The 4-8-metre rock passed just 88,000 kilometres from the Earth on 27 September. That is 0.23 of the distance from the Earth to the Moon.
"In a good month, we find five to 10 near-Earth asteroids, but usually, the ones we discover are as big as mountains, or at least football stadiums, so this one was unique for us," said Edward Bowell, director of the Lowell's Near-Earth-Object Search (Loneos).
Designated 2003 SQ222, the rock was detected 11 hours after its closest approach.
Observations made by professionals and amateurs have allowed its orbit to be determined. It circles the Sun every 1.85 years.
Experts say the object is far too small to have posed a danger to Earth, although it would have been a spectacular fireball had it entered and partially fragmented in our atmosphere.
The previous record for closest approach of an asteroid was 108,000 km in 1994 by an object named 1994 XM1 that was about the same size as 2003 SQ222.