Space Rock's Close Call

Wed. 24 Sept. British Broacasting Company News: --

A small rock about five metres across flew past the Earth a few days ago. Only four other such celestial bodies have come closer since monitoring began. It is actually next to the bright, arrowed object The rock, designated 2003 SW130, was far too small to pose any risk. Had it entered the Earth's atmosphere, it would have fragmented in a spectacular meteor display.

But its detection demonstrates just how efficient astronomers are becoming at picking up such rocks, even those that are the size of a living room.

Half of the top 10 approaches to the Earth by space rocks have been detected in the past two years.

From Venus to the Earth

The rock was discovered about 21 hours after its closest approach by Arianna Glearson and Tom Gehrels observing with the Spacewatch 1.8-metre telescope in Arizona, US.

The following night, the Klet Observatory in the Czech Republic picked it up. It was almost obscured by the glare of Mars which was nearby in the sky.

Observations suggest that it came within about 168,000 kilometres of the Earth at 0600 GMT on 19 September.

It has an orbit that takes it from just inside the orbit of Venus to just outside the orbit of the Earth.

Astronomers are becoming increasingly efficient at detecting small rocks moving in the Earth's vicinity. Last year, they found 2002 XV90 and 2002 MN, which occupy number two and three in the list of close approaches by celestial objects.

'Lots of them'

The closest known approach was 1994 XM1, which came within 112,000 km.

Of course, many large objects do strike the Earth from time to time, such as the Tunguska impactor in 1908.

Brian Marsden, of the Minor Planet Center in the US, said: "There must be lots of objects as tiny as 2003 SW130 that pass closer than the Moon and are missed.

"Spacewatch did a great job finding it, and the Klet Observatory in following it up. Nice cooperation - even if the object would likely burn up high in the atmosphere if it were to hit," he told BBC News Online.

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