Fires From Asteroid May Have Spared Some Regions

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"The computer simulation keeps track of the velocity of material being ejected from the crater," said Kring. "A small fraction of the material achieves escape velocities and, thus, escapes Earth."

The debris ejected from the crater and lofted far above Earth's atmosphere rained back down over a period of about four days, said Kring. As the debris rained down, it heated the atmosphere and surface temperatures so intensely that the ground vegetation spontaneously ignited.

This high energy debris concentrated both around the Chicxulub crater and on the opposite side of the Earth around India, the researchers report.

"The pileup of debris on the opposite of the Earth occurs because material is reaching that spot from all directions," said Kring. "Material launched from the crater in an easterly direction runs into material launched from the crater in a westerly direction."

As the Earth rotated, it turned beneath this returning plume of debris, causing the wildfires to migrate to the west, as illustrated by the researchers' computer simulation of the wildfire spread.

Modeling Assumptions

Some asteroid experts, including Melosh, question the pulsing results of the computer model. "The pulsing is probably the result of the assumed ejecta distribution that they choose, but there is no reason to think that what they do is, in fact, correct," he said.

Melosh believes that the proper way to determine the pattern of wildfire spread is to do numerical simulations of the full ejection process and then follow the velocity and direction of the ejected debris to determine the rain back pattern.

Kring and Durda based their computer simulation of the wildfire spread on models of the Chicxulub impact run by Elisabetta Pierazzo, a research scientist at the Planetary Science Institute in Tucson, Arizona, to determine how impact angle affects the results of impact events.

"We had to estimate what the range in those launch conditions could be for a range of plausible Chicxulub impact events," said Durda. Thus, he added, Melosh is correct to say that their results are only as good as the assumptions in the inputs to the model.

Durda and Kring are currently working on a way to get a direct hand-off of the results from Pierazzo's models of the impact itself to their model that follows the debris trajectories around the planet.

"That will allow us to more rigorously follow changes in our global fire distribution as a result of various impact conditions," said Durda.

Nevertheless, Kring and Durda said that they have run a broad range of possible ejecta launch conditions and certain aspects of the wildfire pattern are the same from model to model, such as the pileup of debris on the opposite side of the Earth from the Yucatan Peninsula.

"Different trajectories can modify the distribution of fires in small ways, but not significantly alter the general pattern," said Kring.

Kring and Durda plan to apply their modeling efforts to other impact events, such as the Manicouagan event in Canada some 200 million years ago and the Popigai impact in Russia some 35 million years ago, to determine the extent of wildfires produced.

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