Asteroid Breakup May Have Doomed Dinosaurs

[American Patriot]

Asteroid Breakup May Have Doomed Dinosaurs
Centauri Dreams ^ | 9/5/07

It’s a disaster scenario that Hollywood has picked up on (think Deep Impact). An incoming object menaces the Earth. Scientists try to destroy it with nuclear weapons, but the horrified populace soon discovers that the blast has simply broken the object into pieces, each with the potential to wreak havoc planet-wide. Now we learn that an impact between two asteroids causing a similar crack-up may have resulted in the cataclysmic event some 65 million years ago that destroyed the dinosaurs.

Researchers from Southwest Research Institute and Charles University (Prague) have been studying the asteroid (298) Baptistina, combining their observations with numerical simulations to model the impact event. As the theory goes, Baptistina’s parent body, some 170 kilometers in diameter, was hit by another asteroid approximately 60 kilometers wide. The result: The Baptistina asteroid family, a cluster of fragments in similar orbits that once included 300 bodies larger than 10 kilometers and 140,000 bodies larger than one kilometer.

Asteroid strike on Earth

With all the characteristics of a carbonaceous chondrite meteorite, the Baptistina parent asteroid makes a nice match for the impactor that created the Chicxulub crater in the Yucatan. Sediment samples show that it, too, had a carbonaceous chondrite composition, and the team’s simulations produced a ninety percent probability that it was indeed a member of the Baptistina family. Moreover, the simulations indicate that the lunar crater Tycho may also have been produced by an impactor with a Baptistina pedigree.

The original breakup is thought to have occurred some 160 million years ago, after which the fragments’ orbits would have evolved as they absorbed sunlight and re-radiated energy away as heat. Many of the fragments escaped the main asteroid belt and became potential Earth-crossers. The researchers believe that about two percent of these objects actually went on to strike Earth. Call it the ‘Baptistina bombardment,’ a surge in impacts that peaked 100 million years ago.

“We are in the tail end of this shower now,” says William Bottke (Southwest Research Institute). “Our simulations suggest that about 20 percent of the present-day, near-Earth asteroid population can be traced back to the Baptistina family.”

The impact histories of both Earth and Moon seem to support the supposition, showing a two-fold increase in the formation rate of large craters over the past 100 to 150 million years. That should make an emphatic point about the asteroid belt: Its history of collision and orbital change may well play a significant role in the history of our planet. We need to develop and deploy the tools that can alter the orbits of potential impactors, or do we want to assume that our inadequate catalog of Earth-crossing objects will give us time enough to act?

The paper is Bottke et al., “An asteroid breakup 160 Myr ago as the probable source of the K/T impactor,” Nature 449 (September 6, 2007), pp. 48-53 (abstract).

[American Patriot]

Czech scientists: extinction of dinosaurs was caused by asteroid collision

[10-09-2007] By Ruth Frankova

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65 million years ago a huge cosmic body crashed into the Earth, causing large fires all over the globe. The sudden change of climate wiped out most of the planet's vegetation and species, including the dinosaurs. Scientists have long argued whether the Earth was hit by a comet or an asteroid. Until recently, chemical evidence indicated it was a comet. Now, however, a team consisting of two Czech and one US scientist has come up with new facts.



The trace of the collision called Tertiary Mass Extinction can be still seen today at the Yucatan peninsula in Mexico. It is a huge crater with a diameter of about 180 kilometres. Not long ago, a team of three scientists, including David Vokrouhlicky of the Astronomical Institute of Charles University, collected some sediment samples at the site of the clash and made some interesting discoveries.


David Vokrouhlicky, photo: utf.mff.cuni.cz
"The basis of our work was the discovery of a new asteroid family - a group of asteroids that share roughly the same orbit around the Sun and have about the same mineralogy of their surface which points to their common origin in a break-up of a larger asteroid, that was hit by another asteroid and got disrupted into pieces. What we observe now are fragments of this larger precursor."


The discovery of a new group of asteroids is not that exceptional. What is, however, is that the Baptistina family (as the new group of asteroids is called) contains minerals that are very similar to those in comets. On top of that, Mr Vokrouhlicky explains, the location of the asteroids makes them a much more likely missile than the comet.



"The Baptistina family is special in terms of its location in what we call the main asteroid belt, its age and the size of its precursor. The special thing about the conjunction of the three things related to the Baptistina family is that it is located in the inner part of the main belt of asteroids. It is much easier to transfer asteroids from the inner part into planet crossing orbits than from the outer part. So Baptistina is sort of strategically located to provide fragments into orbits, which cross the orbits of the Terrestrial planets: Mars, Earth, Venus and Mercury."


According to the scientists, about twenty percent of the asteroids circulating close to the Earth today can be traced back to the Baptistina family.