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Professor solves a meteor mystery

Last September, something strange landed near the rural Peruvian village of Carancas. Two months later, so did Peter Schultz.

One was an extraterrestrial fireball that struck the Earth at 10,000 miles per hour, formed a bubbling crater nearly 50 feet wide and afflicted local villagers and livestock with a mysterious illness. The other is the Brown geologist who may have figured out why.

The fiery mass shot across the morning sky bursting and crackling like fireworks, villagers said after the Sept. 15 impact. An explosive crash tossed nearby locals to the ground, shattered windows one kilometer away and kicked up a massive dust cloud, covering one man from head to toe in a fine white powder. Many thought the streaking fireball - brighter than the sun, by some accounts - was an aerial attack from neighboring Chile.

Curious shepherds and farmers approached the crash site to find a smoking crater reminiscent of a Hollywood film, laden with rocks and stirring with bubbling water that emitted a foul vapor. But curiosity turned to fear when unexplained symptoms began to crop up in Carancas: headaches, vomiting and skin lesions struck more than 150 villagers, Peru's Ministry of Health stated days later. Locals reported that their animals lost their appetites and bled from their noses. Children were restless and cried through the night.

But according to Schultz, the professor of geological sciences who visited the site last December, the true mystery in Carancas is how any of this happened in the first place.

Sophisticated theory and conventional wisdom have long agreed that most meteors break into fragments and fizzle out before they can reach the Earth's surface. Even those large and durable enough to make it through the atmosphere hit the ground as ghosts of their former selves, "plopping out of the sky and forming a bullet hole in the Earth," Schultz said. "This meteor crashed into the Earth at three kilometers per second, exploded and buried itself into the ground."

Last month, Schultz delivered a highly anticipated lecture at the 39th Lunar and Planetary Science Conference in League City, Texas. And if he's right, the bold theory he proposed there may shake loose a "gut response" entrenched within the geological, physical and astronomical sciences: "Carancas simply should not have happened."

A Web of speculation

The handful of shepherds who happened to lead their Alpaca herds near the arroyo that day may have been the first humans ever to witness an explosive meteor impact. But the rest of the world quickly got its chance, if vicariously, through a flurry of activity in the blogosphere.

Hundreds of scientists, journalists and captivated amateurs weighed in on the bizarre events as they unfolded, offering scores of pet theories and radically revising them as more information streamed in from Peru.

Pravda, a Russian online newspaper born out of a print version run by the country's former Communist Party, ran the headline "American spy satellite downed in Peru as U.S. nuclear attack on Iran thwarted" five days after the impact. The story attributes the villagers' illness to radiation poisoning from the satellite's plutonium power generator.

Other proposed explanations were less sensational. Nevadan wildlife biologist and amateur geologist David Syzdek wrote a Sept. 18 blog post titled "Meteorite strike in Peru gassing villagers? Maybe not." In it, he proposed that a mud volcano producing toxic gases was responsible for both the illness and the crater.

"The Andes are very active geologically so I think there is a good possibility that this crater was caused by an outburst of geothermal activity," he wrote.

As for the blinding light shooting across the sky, Syzdek chalked it up to coincidence.

"Fireballs are quite common," he wrote. "One possible scenario is that the people who saw the fireball just happened on a recently formed mud volcano while they were out looking for the fireball impact site."

Though Pravda and Syzdek drew radically different conclusions from the reports, what they shared with each other, many bloggers and even some scientists was a healthy skepticism about reports coming out of Peru. Pravda and Syzdek both pointed out in their posts that an explosion powerful enough to create such a large crater would be equivalent to 1,000 tons of TNT, or a tactical nuclear strike.

"When I first saw the news reports, they just didn't seem right," Syzdek later said in an interview. "Explosive impacts like this just don't happen."

'A hyperspeed curveball'

Gonzalo Tancredi, a Uruguayan astronomer who collaborated with Schultz in Carancas, said initial reports of the impact confounded amateurs and Ph.D.s alike. Bewildered scientists even entertained the possibility of a hoax as rumors floated around the scientific community.

"At the beginning, there were some doubts about what really happened there," Tancredi said. "We thought maybe it was a meteor fall or maybe it was something else, even something fake."

But when Tancredi visited Carancas a few weeks later, what he observed silenced the conspiracies and pointed unequivocally to one conclusion.

Tancredi interviewed locals, who reported a large mushroom cloud that formed over the crater and compression waves that knocked villagers to the ground. He also found pieces of soil and rock that had been launched over three football fields from the crater - one piece even pierced the roof of a barn 100 meters away. Combined with analyses of infrasound detectors and the patterns of crater "ejecta," the evidence pointed to a genuine and very powerful meteorite impact.

But the question that remained on everyone's mind was how the meteor got there at all - a scientific riddle that was made even more challenging by Michael Farmer.

Farmer is a controversial figure in the geological community. He is a meteorite hunter, a poacher of alien rocks who travels to impact sites around the world - usually the "bullet hole in the Earth" type mentioned by Schultz - and collects whatever he can find, often brushing up against authorities and other hunters. Meteorite hunting is Farmer's full-time job; he profits from selling what he finds.

Farmer, who said he is "totally self-taught" when it comes to meteors, said he was as skeptical as the rest when he first heard the reports coming out of Peru while on hunt in Spain. But 16 days later, he and his partners found themselves staring into the Carancas impact crater, the first Americans on the scene - and they stumbled on an extraterrestrial gold mine.

"We got there and just started picking up pieces off the ground," Farmer said. "The entire ground was white, just white powder which was all meteor."

Farmer and his team eventually accumulated 10 kilograms of small meteorite fragments and sold them to private collectors and universities for an astronomical $100 per gram.

But despite his rocky past with the geological community, Farmer and his expensive fragments made a priceless contribution to scientists. Within minutes of arriving on the scene, Farmer discovered that the Carancas meteorite was a chondrite, or stony meteorite, as opposed to an iron meteorite.

Though far more common than iron meteorites, chondrites are highly vulnerable to ablation - the cracking, eroding and even exploding that occurs when a meteor enters the atmosphere and undergoes extreme changes in temperature and pressure. As a result, chondrites are far less likely than the more durable iron meteorites to make it to the Earth's surface in large pieces - which makes the Carancas meteorite all the more baffling.

"For a while, the only information we were getting was from Farmer's Web site," Schultz said. "This was not the type of object you'd expect to get through the atmosphere in a tight clump."

With most pieces of the geological puzzle on the table, the stage was set for Schultz to visit the site for himself. But when he arrived there in December with a Brown graduate
student, Tancredi and Peruvian astrophysicist Jose Ishitsuka, a budding geologist actually made the crucial discovery. Scott Harris GS said he collected some soil samples "initially out of curiosity" to look for evidence of shock deformation, which occurs when an object rapidly decelerates in cases like impacts or explosions. When Harris looked at the material under a microscope, he found tiny mineral grains that had turned into glass because of heat and massive shock forces, indicating a very high-speed impact. Here was yet another mystifying piece of evidence.

"At the minimum," Harris said, "this would support a velocity of three kilometers per second - a real high-velocity explosion instead of just a plop in the ground."

By this time, more reputable scientific theories of the impact had supplanted the initial speculation, the most popular of which came from a group in Germany and Russia. They proposed that the meteor entered the Earth's atmosphere at a very shallow angle, allowing it to reach the surface gradually and avoid a sudden increase in pressure - "the difference between diving in and doing a belly flop," Schultz said.

But their theory's relatively low impact velocity of 180 meters per second, or about 400 miles per hour, was consistent with every piece of evidence but Harris', which pointed to a velocity of about 10,000 miles per hour at impact.

"This was nature's way of throwing us a curveball," Schultz said. "A hyperspeed curveball."

Changing shape, changing theory

Back home in Providence, Schultz was now faced with the task of fitting the puzzle pieces together into a cohesive theory. And to do it, he looked to Earth's closest planetary neighbor, Venus.

"Our models make predictions about what kind of objects can make it to the surface at what velocity, and the Carancas meteor isn't usually one of them," Schultz said. "But Venus has a much denser atmosphere and we still find craters on its surface. How did they get there? I think it might be the same thing here."

To explain the alternative theory he developed, Schultz compared a typical meteor's descent to a waterskier behind a boat.

"Normally when you're on the outside of the wake, you're pushed out further," Schultz said. "From my experience looking at Venus, I realized that there was a certain condition where the waterskier will stay inside the wake, and actually get pushed inward."

At last month's Lunar and Planetary Science Conference, Schultz proposed that the meteor did break up into pieces, but shock waves created by the speeding mass may have kept them close together. And since the meteor descended as a clump of fragments instead of one large piece, it reshaped itself along the way to become more aerodynamic, like a football or a javelin cutting through the air instead of a poorly shaped hunk of rock.

"It's like having a Volkswagen turn into a Ford Taurus," Schultz said, adding that this sort of reshaping is well known to geologists who study islands and land-water interaction. "If you put a big pile of dirt in a stream, that mound will eventually turn into a teardrop shape. It's trying to minimize the friction."

Tancredi, who co-authored the paper with Schultz, Harris and Ishitsuka, said Schultz's theory is gaining popularity but is still being debated, even among the group that proposed it.

"This is the hot question right now," he said. "We still have to demonstrate that this phenomenon is possible."

In the meantime, another hot question had remained without a definitive answer - the etiology of the strange illness that afflicted the people of Carancas. But the group may solve that mystery, too.

Schultz, Harris and Tancredi all dismissed the possibility of the meteorite emitting harmful gases that would sicken villagers. Instead, they proposed a simpler cause: the power of the mind.

The meteorite impact sent out a powerful compression wave that knocked nearby villagers and animals to the ground and injected the soil with air, which later bubbled up through the crater. Shepherds and cattle may also have breathed in the thick dust thrown up by the crash and smelled the sulfurous gases produced as water reacted with iron sulfide in the meteor.

But what the group thinks later spread through the town was not disease, but panic.

"We think it was probably more of a psychological response," Harris said, adding that commonplace symptoms like headaches and nausea could easily have been caused by the disorienting impact and then mirrored by frightened villagers.

Harris also admitted the possibility of the meteorite releasing arsenic deposits, which are known to exist in Peru, but said it would be very unlikely for those gases to have caused the illness.

"In order to really get arsenic poisoning, you'd need high concentrations," he said. "You'd have to be there inhaling the vapor filled with the stuff right after the meteorite hit."

Poisonous or not, the Carancas meteorite could have important implications for public safety. Tancredi said there's no reason an impact like this couldn't happen in a major city, wiping out a few city blocks. He also pointed out that today's most advanced meteor detectors aren't nearly powerful enough to detect an object as small as the Carancas meteorite.

"Near-Earth detectors detect objects that could create a global catastrophe, something maybe a kilometer across," he said. "We don't have any kind of technology that could detect this object before reaching the atmosphere, so it will not be possible to know when and where one of these objects could strike again."

But Schultz said the most important lesson to learn from Carancas is that the foundation of good science is hard empirical evidence, even - and especially - when it contradicts established principle.

"We tried to understand what the rocks told us rather than looking at the theory," he said. "Nature trumps theory, every time."


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