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Dino-killing meteorite identified

Scientists say collision in asteroid belt led to mass extinction

By Paul Voosen
Staff Writer, The Prague Post
September 19th, 2007 issue

The extinction of the dinosaurs was 100 million years in the making.
In the most prominent recent case of collaboration between Czech and U.S. scientists, a team of researchers has identified the interstellar collision that was the likely source of a meteorite that plummeted into the Yucatan Peninsula 65 million years ago — a strike believed to have caused the extinction of 70 percent of the planet’s species, including the dinosaurs.
The team’s investigations began modestly, attempting to account for a strange spread in impact craters on the Gaspra asteroid, said David Vokrouhlický, an astronomer at Charles University and co-author, along with William Bottke and David Nesvorný of the Southwest Research Institute, of a paper on the topic that appeared in the U.S. journal Nature Sept. 5.
“It hit us that a recent breakup of a large asteroid in the inner belt might be the solution,” he said.
The team then identified Baptistina, a family of asteroids, as a possible source. After vigorous rounds of computer modeling, the researchers established that Baptistina was created by a violent crash 160 million years ago between two large asteroids of approximately 170 kilometers (106 miles) and 60 kilometers in diameter, respectively.
After the impact, remnants of Baptistina, which included some 300 bodies larger than 10 kilometers, escaped the asteroid belt by drifting into a “dynamical superhighway” that set their course for Earth, resulting in a twofold increase in asteroid strikes over the past 100 million to 150 million years, peaking 100 million years ago, Vokrouhlický said.
Following their re-created trail, the team then investigated the composition of the Yucatan’s 180-kilometer-wide Chicxulub crater. Studies of the crater’s sediment eliminated many other potential asteroids, leading the researchers to state that there is a “90 percent probability that the object that formed the Chicxulub crater was a refugee from the Baptistina family.”
While a general consensus has formed in the scientific community that whatever struck the Yucatan was responsible for the extinction of the dinosaurs, it has been an open debate as to how exactly the extinction occurred, possibly through a cocktail of catastrophes that included a global cloak of ash, wildfires and the impact itself, which would have been 2 million times stronger than the largest nuclear weapon ever detonated.
Also debated has been whether it was an asteroid or comet that flattened Chicxulub. The research team’s findings seem to tip the consensus to the former.
The Baptistina breakup is likely the largest crash to occur in the past 200 million years of the inner asteroid belt, which is closer to Mars, Vokrouhlický said. The outer belt saw a similar impact only 8.2 million years ago, but — fortunately enough — that collision’s location prevented any escaping asteroids from heading toward Earth.
Today, the Baptistina collision represents the source of 20 percent of all the large asteroids located near Earth, Vokrouhlický said. Many more craters can be tied to Baptistina, beginning with the Moon’s distinctive Tycho crater.
“It is likely that more breakup events in the asteroid belt are connected in some fashion to events on the Earth, Moon and other planets,” Bottke said when announcing their findings. “The hunt is on!”

Paul Voosen can be reached at pvoosen@praguepost.com


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