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San Antonio-Based Research Institute Zeroes In On Dino-Killing Asteroid

New research reveals a large asteroid breakup to be the likely source of the impactor that caused a mass extinction event on Earth 65 million years ago.
New research reveals a large asteroid breakup to be the likely source of the impactor that caused a mass extinction event on Earth 65 million years ago.

A team of researchers from the San Antonio-based Southwest Research Institute combined computer models of asteroid evolution with observations of known asteroids to determine where the dinosaur-killing asteroid might have come from.

They found that it likely came from the outer half of the main asteroid belt and, perhaps more importantly, how often asteroids of that size hit Earth.

The 6-mile-wide asteroid created the Chicxulub crater more than 90 miles wide off Mexico's Yucatán Peninsula some 66 million years ago. So what are the odds of a similar-sized asteroid hitting the Earth in the future?

The lead researcher David Nesvorny said we have millions of years to relax.

"We found that it's typical that one 10-kilo meteor or larger impacts on the earth every 250 million years," he said.

Nesvorny said the research was driven by the question where might the siblings of the Chicxulub impactor be hiding in space. The outer half of the main asteroid belt was previously thought to produce few impactors.

To probe the Chicxulub impact, geologists have previously examined ancient rock samples found on land and within drill cores. The results indicate the impactor was similar to the carbonaceous chondrite class of meteorites, some of the most pristine materials in the solar system.

While carbonaceous chondrites are common among the many mile-wide bodies that approach the Earth, none today are close to the sizes needed to produce the Chicxulub impact with any kind of reasonable probability, according to a news release from the institute.

To explain their absence, several past groups have simulated large asteroid and comet breakups in the inner solar system, looking at surges of impacts on Earth with the largest one producing Chicxulub crater,” said William Bottke, one of the paper’s co-authors.

“While many of these models had interesting properties, none provided a satisfying match to what we know about asteroids and comets. It seemed like we were still missing something important," he said.

To solve this problem, the team used computer models that track how objects escape the main asteroid belt, a zone of small bodies located between the orbits of Mars and Jupiter.

Over eons, thermal forces allow these objects to drift into dynamical “escape hatches” where the gravitational kicks of the planets can push them into orbits nearing Earth.

Using NASA’s Pleaides Supercomputer, the team followed 130,000 model asteroids evolving in this slow, steady manner for hundreds of millions of years. Particular attention was given to asteroids located in the outer half of the asteroid belt, the part that is furthest from the Sun. To their surprise, they found that 6-mile-wide asteroids from this region strike the Earth at least 10 times more often than previously calculated, the news release stated.

“This result is intriguing not only because the outer half of the asteroid belt is home to large numbers of carbonaceous chondrite impactors, but also because the team’s simulations can, for the first time, reproduce the orbits of large asteroids on the verge of approaching Earth,” said another researcher, Simone Marchi. “Our explanation for the source of the Chicxulub impactor fits in beautifully with what we already know about how asteroids evolve.”

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Brian Kirkpatrick has been a journalist in Texas most of his life, covering San Antonio news since 1993, including the deadly October 1998 flooding, the arrival of the Toyota plant in 2003, and the base closure and realignments in 2005.