After a massive fireball smashed into southeastern Peru last fall, scientists dismissed a shot-down spy satellite as the cause. But many questions remain about the unusual crater it left behind. Andrew Westoll reports

When the Pentagon announced last Monday that it had successfully shot down a wayward U.S. spy satellite, political-conspiracy theorists went wild. Officials called the cosmic potshot a matter of international security - the bus-sized satellite, too big to burn up on re-entry, was carrying more than 500 kilograms of toxic hydrazine gas - but America-watchers worldwide wondered aloud whether the satellite story was a pretext for the U.S. military to flex its space-racing muscles.

For me, though, the event reminded me not of the Star Wars debate, but instead whisked me back to a tiny farming village in southeastern Peru I had visited last November.

I had travelled to the hamlet of Carancas, located a llama's throw from the Bolivian border on the stark plains of the Andean Altiplano, to investigate the Carancas crater, another cosmic event that had also been shrouded in conspiracy theories and, more recently, has posed a profound scientific riddle.

On Sept. 15 of last year, at 11:45 in the morning, a massive fireball streaked across the sky above southeastern Peru and slammed into a dry stream bed in Carancas.

The resulting explosion shook the earth and threw a mushroom cloud of corkscrewing smoke and scorched rock hundreds of metres into the air. Hundreds of Aymaran villagers, who had otherwise been enjoying a restful Saturday, flocked to the site to see what had happened.

The impact made international headlines and set the Internet alight with rumours - 600 villagers were rushed to the hospital; police confiscated fragments of the extraterrestrial object and sold them to rabid American space-junk collectors; the Russian tabloid Pravda said the impact was caused by a downed American spy satellite and the mass sickness was the result of hydrazine leakage from its fuel tank - a claim that seemed laughable at the time, but now seems frighteningly within the realm of possibility.

Meanwhile, it took scientists from Lima a week to visit the site, during which time the prevailing wisdom among locals was that Chile had dropped a bomb on them.

In time, most of these rumours were laid to rest. Scientists confirmed that the object that landed in Carancas was a meteorite; that roughly 30 villagers had developed nausea and headaches - likely symptoms of mild psychological trauma and not, as many had claimed, a Michael Crichton-style Andromeda strain; and that Peru was not at war with its southern neighbour.


At the same time, though, a bona fide scientific mystery was presenting itself. Out of that blackened hole in the Peruvian high plain emerged a puzzle that threatens to turn the science of crater formation on its head.

"The Carancas impact crater should not have happened," says Dr. Peter Schultz, a professor of planetary impacts in the geological sciences Department at Brown University and the lead author of a paper on the Carancas event to be given this month at the Lunar and Planetary Science Conference in League City, Tex.

For researchers who have relied for years upon an established model, Dr. Schultz says, the Carancas meteorite has thrown a "hypervelocity curveball."

An analysis of fragments suggest that the Carancas object was an ordinary chondrite, or stony meteorite, a remnant from the ancient asteroid belt that spawned the planets of our solar system. Chondrites, being relatively weak, typically lose most of their velocity as they enter the Earth's atmosphere. They ablate, or burn up, and break into fragments, which land with little fanfare at a speed of no more than 100 and 150 metres per second - as if they had simply been dropped from an airplane.

This is not what happened at Carancas.

"Although we don't know what size it was when it entered the atmosphere," Dr. Schultz says, "the fact is, by the time is got through, this thing was still more than a metre wide and still going incredibly fast."

Acoustical data reveal that the Carancas meteorite was travelling at a speed of four to six kilometres a second. The resulting hole in the ground has all the characteristics of an impressive "shock-produced" crater, as opposed to the far less dramatic "penetration" craters usually caused by chondrites: It's circular, nearly 15 metres wide, at least three metres deep, has a well-defined rim and a long ray of ejected debris stretching more than 300 metres to the southwest. A nearby house had a hole punched through its metal roof by a flying piece of stone. Seismic evidence suggests that the meteorite landed with a force equivalent to the detonation of more than two tonnes of TNT.

"When this thing landed," Dr. Schultz says, "many of us said, 'No. This can't be.' Up until now, conventional wisdom has been that these sorts of small craters are caused by iron meteorites, not stone."

Although chondrites are the most common type of meteorite to enter the Earth's atmosphere, they account for only about 5 per cent of those that make it through intact. The majority of meteorites found on the ground are made of much heavier iron, which is more likely to survive the baptism-by-fire of atmospheric entry.

"Without Carancas," Dr. Schultz says, "we wouldn't have known this was possible."

The event has sparked an ongoing collaboration among researchers in Canada, the U.S., Peru, Bolivia and Uruguay. But Dr. Schultz admits to having an early favourite among the theories to explain Carancas. It stems from a surprising discovery he and his colleagues made while working on the National Aeronautics and Space Administration's Magellan Mission to Venus in the early 1990s.

"We found that when you increase the atmospheric pressure on a cloud of debris, individual particles tend to line up in a narrow, needle-like fashion," Dr. Schultz says. "They align themselves like a flock of geese does in order to reduce the aerodynamic drag."

He wonders if the Carancas chondrite did, indeed, break up upon entry, but then the fragments reshaped themselves into a sort of extraterrestrial drill, maintaining much of their speed and then boring into the ground one after the other in rapid succession.

Whatever the explanation, the Carancas event has sent a shockwave of second-guessing throughout this small corner of the planetary sciences. Conventional models of meteorite cratering and entry physics may need to be recast. Circular depressions on the Earth's surface that had previously been dismissed as potential craters because of the absence of iron may, indeed, be meteor footprints. And chondrites may be contributing more than initially thought to the surface composition of planets such as Mars, where a number of similar small craters have been found.


Comment: In other words, impacts from cometary and asteroidal debris may be much greater than previously thought.


"I wouldn't say we're grasping at straws here," Dr. Schultz says, with the laugh of a scientist who has glimpsed the impossible. "But nature sure is amazing. And, well, we're essentially grasping at straws."

When I arrived at the Carancas crater site two months after the event, I found the surrounding high plains cold and deserted. I gazed into the pond of murky water that had collected at the bottom of the crater and tried to imagine it roiling violently, a column of blue smoke spiralling into the air. Then a chorus of voices reached me from a far-off church and three Aymaran ladies appeared, wrapped in traditional cloaks and skirts.

They told me that they won't know how to feel about the meteorite until next year's harvest. Only then will they decide if it was a good meteor - un meteoro simpatico - or a bad one. These ladies and their neighbours may have been the first humans in recorded history to witness the formation of an impact crater, but they didn't seem impressed. Their goal, they said, was to dig up the meteorite and put it on display, right next to the crater, for tourists.

Comment: They may be the first humans to witness and survive the formation of an impact crater.


Sadly, the meteorite, or what remains of it, may never be recovered. Chondrites tend to ionize and dissolve in water, and as I write this, the rainy season is arriving in southeastern Peru.

As for the crater itself, experts believe that, without the resources to protect it, this remarkable site and the mysteries it spawned may soon be washed away.

Andrew Westoll is a writer who lives in Toronto. His first book, The Riverbones, is a travel memoir set in Suriname and will be published this fall by McClelland & Stewart.