Dinosaur-Killing Asteroid Came From The ‘Dark Corners’ Of Our Solar System

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A meteorite about 10 kilometers (6.2 miles) in diameter believed to have wiped out about 76% of all species on Earth – including dinosaurs – some 66 million years ago likely came from the outer half of the main asteroid belt, a region previously thought to produce few impactors.

The impact formed the Chicxulub crater, which is around 200 kilometers (90 miles) wide, along the coast of the Yucatan Peninsula. The impact would have thrown trillions of tons of dust into the atmosphere, cooling the Earths climate significantly, which may have been responsible for the mass extinction. A layer of iridium-rich clay marking the boundary betwee the Cretaceous and Paleogene period is thought to be the remnants of the impact debris.

Researchers from the independent Southwest Research Institute (SwRI) in San Antonio, Texas, combined chemical traces of the impactor preserved in the impact crater, observations of the trajectories of known asteroids and computer models to investigate the origin and frequency of so-called Chicxulub events.

Geologists have previously examined 66-million-year-old rock samples recovered from drill cores within the Chicxulub crater. The results indicate the impactor was similar to the carbonaceous chondrite class of meteorites, believed to be primordial leftovers of the solar system’s formation.

While carbonaceous chondrites are common meteorites, none today are close to the sizes needed to produce the Chicxulub impact.

“We decided to look for where the siblings of the Chicxulub impactor might be hiding,” said study lead author Dr. David Nesvorný in a statement published by the SwRI.

“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 Dr. 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.”

The researchers used computer models that track how objects escape the main asteroid belt, a zone of small planetary bodies located between the orbits of Mars and Jupiter. Over eons, gravitational forces can push asteroids 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 10-kilometers-wide asteroids from this region strike the Earth at least 10 times more often than previously calculated.

“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 co-author Dr. 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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