According to the Earth Impact Database, a resource maintained by the Geological Survey of Canada and University of New Brunswick, only 173 such impact craters have been discovered in the world. The find will likely deliver a lifetime of peer group kudos to Dr Hickman, a government geologist with the Geological Survey of Western Australia.

"I wasn't looking for it," Dr Hickman recalled in a telephone interview. "I was high up in Google Earth [the free program that enables users to scour the Earth using stitched together aerial and satellite images] when I spotted this little circular structure which struck me as odd." Dr Hickman, who heads his organisation's Pilbara Craton Mapping Project, says he made the discovery last July while he was looking for possible sites of channel iron deposits - highly sought after alluvial deposits from which the ore can be extracted very cheaply. Although the crater is situated about 1000 kilometres north-east of Perth and more than 300 kilometres south-east of Port Headland, it is only 35 kilometres north of the mining town of Newman in an area that has been previously surveyed.

Dr Hickman referred his find to Dr Andrew Glikson, an impact crater expert who is a visiting fellow at the Australian National University's Research School of Earth Sciences. Dr Glikson, who has been studying impact craters since 1968, visited the site in August and corroborated Dr Hickman's hypothesis.

"It's a little beauty," he said in a telephone interview. "It's an absolute gem in terms of youth and preservation." He said the only other explanation for the formation - which is about the same size as the Melbourne Cricket Ground - is a volcanic eruption. But the lack of young volcanic material in area surrounding the crater rules this theory out.

"No other process could have created this type of crater," said Dr Glikson, who estimates the meteorite was between 10 to 15 metres in diameter when it slammed into the Earth. The two geologists - together with a third scientist - have written and submitted a paper on the discovery to the Australian Journal of Earth Sciences, where it will be subjected to peer review.

The next step in the process of formal identification involves returning to the site and trying to find shards of meteorite that have been left behind, or examples of terrestrial rocks that have been fused together with extraterrestrial matter as a result of the violent impact. Dr Hickman, who hopes to visit the site for the first time in May, says the site is about half a day's drive north from the town of Newman following the privately-owned rail line to Port Headland, which is famous for its mile-long trains. He said it was Dr Glikson's decision to name his find the Hickman Crater. "I'm not that conceited," he said modestly.

Dr Glikson, who also has another crater in Western Australia named after him, says he couldn't explain why the crater hadn't been found before. "This one stands out like a sore thumb on Google Earth," he said.

The crater site can be seen on Google Maps (see embedded map, above right) and on Google Earth (requires download).

