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University of Alberta researchers have discovered one of the youngest impact craters in the world.

It was formed after a hunk of asteroid hurtled to Earth 1,100 years ago and smashed into the west central part of what is now Alberta, and is one of only 10 craters in the world that date to within the past 10,000 years, says meteorite expert Chris Herd.

The bowl-shaped scar was hidden by trees about 200 kilometres west of Edmonton near Whitecourt. Local hunters thought it was a sinkhole.

But some residents suspected it was a crater, and went looking for space rocks with metal detectors. In July, 2007, they contacted Dr. Herd after finding several pieces of metallic rock next to a large hole in the ground. Tests confirmed they were meteorite fragments, and that the hole was part of a crater.

"I was skeptical," says Dr. Herd, lead author of a paper on the discovery published in this month's edition of the journal Geology.

But the residents, who he says have asked to remain anonymous, were right.

Dr. Herd and his colleagues tried to see the entire crater on satellite images, but it was covered with too many aspen trees and shrubs.

Duane Froese, an assistant professor in the department of earth and atmospheric sciences, suggested they try LiDAR, a remote-sensing technology that uses laser light bounced from the Earth's surface.

Using LiDAR data, they created an image of the area without any vegetation. It revealed a crater 36 metres wide and six metres deep.

That's peanut-sized compared to the 180-kilometre-wide crater in Mexico created 65 million years ago when an asteroid or comet 10 to 15 kilometres in diameter smashed into the Yucatan Peninsula. That cataclysmic collision has been linked to the demise of the dinosaurs and 70 per cent of other species that were alive at the time.

The Whitecourt event would have been much less explosive. It probably wasn't much of a fireball, but would have flattened trees. It is hard to know exactly how much damage it would cause if it hit today, says Randy Kofman, a graduate student who worked on the paper. "If it had hit a building, it would certainly have done considerable damage," says Mr. Kofman.

The researchers are still working out how big it was, but they estimate it was roughly one metre in diameter, and was likely travelling at two kilometres per second when it landed.

It was composed mostly of iron with some nickel. It was probably a hunk from the core of an asteroid that originated between the orbits of Mars and Jupiter that was formed 4.5 billion years ago.

It created the youngest and best preserved crater in Canada, says Dr. Herd.

Small craters like this one are rare because they tend to disappear over time with erosion. Similar craters have been found on the surface of the moon and Mars.

Some researchers say the Earth's surface should have more craters like it. LiDAR could be a new tool to find them, says Dr. Herd.

It is also one of less than a dozen craters in the world found littered with hunks of space rock. So far, 160 meteorites have been recovered. Some are the size of small grains - less than a centimetre across, while others measure 10 cm and weigh over a kilogram.

Meteorites can be sold for thousands of dollars, but the crater and the surrounding area have been designated a provincial historic resource, says Dr. Herd. Anyone who disturbs the area or tries to collect rocks there could face a fine of up to $50,000 or a year in jail.

Search begins for fireball fragments

University of Calgary researcher Alan Hildebrand headed to western Saskatchewan yesterday to look for remnants of the fireball that flashed across the Alberta boundary last Thursday night.

He says tens of thousands of people saw it streak across the sky, observed a blue flash and heard a number of explosions.

The asteroid fragment weighed approximately 10 tonnes when it entered the Earth's atmosphere, says Peter Brown, Canada research chair in meteor physics at the University of Western Ontario.

It is likely more crumbly than the rock that created the crater near Whitecourt 1,100 years ago.

"Many witnesses reported seeing a cluster of red fragments continuing downwards in the sky after the fireball exploded. These represent the rocks slowing down that will eventually fall to the ground as meteorites," Dr. Brown says. He expects they will be scattered in area about eight kilometres long and three kilometres wide, with larger stones to the southeast.

They can be worth a lot of money, he says, as would be the property of the person who owns the land where they are found. Anne McIlroy

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A tale of two meteorites

Alberta researchers are tracing the history of two space rocks. The first cratered in the west central part of the province roughly 1,100 years ago. The second streaked through the sky Thursday night.

THAT WAS THEN

900 AD

Size: The chunk of asteroid is estimated to have been a metre in diameter.

Impact: It didn't break up before it hit the ground and carved a crater.

Location: Whitecourt, 200 kilometres west of Edmonton. Scientists used remote sensing technology called LiDAR to find the crater, which was hidden by trees.

Speed: It was travelling an estimated two kilometres per second when it hit.

The rock: A hunk of iron mixed with nickel.

THIS IS NOW

Last Thursday

Size: It weighed about 10 tonnes when it entered Earth's atmosphere.

Impact: It broke up before it hit the ground, scattering debris that scientists are hoping to recover.

Location: The fireball lit up the skies of Alberta and Saskatchewan, and the scientists hope to locate the space rocks in Western Saskatchewan.

Speed: It was travelling at 14 kilometres per second.

The rock: More crumbly, with iron distributed throughout.

THE GLOBE AND MAIL // PHOTO: ANDREW BARTLET