Large asteroids like the one that wiped out the dinosaurs may be more common than previously thought, scientists have discovered.
The space rock that caused the dinosaurs' extinction, known as the Chicxulub impactor, is thought to have slammed into our planet about 66 million years ago.
The asteroid, around 10 kilometers wide, produced a blast equal to 100 million megatons that devastated the Gulf of Mexico region, triggered a mass extinction event and produced a crater around 180 kilometers across.
Scientists have previously questioned where the Chicxulub impactor came from and how often impacts like it have occurred. To find an answer, researchers from the Department of Space Studies at the Southwest Research Institute (SRI) in Colorado used NASA's Pleiades supercomputer to model how asteroids from the outer half of the asteroid belt might end up colliding with the Earth.
The asteroid belt is a vast ring of space rocks that circles the sun between the orbits of Mars and Jupiter.
David Nesvorný, lead author of the pre-print paper describing the SRI research, said in a statement: "We decided to look for where the siblings of the Chicxulub impactor might be hiding."
The researchers found that 6-mile-wide (10 km) asteroids from this region hit the Earth at least 10 times more often than previously thought.
Thankfully, such impacts are still rare. The SRI team states that the occurrence rate of asteroid impacts from space rocks bigger than 5 kilometers wide is between 16 and 32 every billion years.
The SRI paper also states that the Chicxulub impactor is likely to have come from a distant part of the asteroid belt and its chemical composition is unusual, leading the researchers to suggest that the Chicxulub asteroid was "a special circumstance."
According to the study, most asteroid impacts that have been recorded are classed as ordinary chondrites (OCs), based on their composition.
This is backed up by theoretical models that show the vast majority of asteroid impacts came from the innermost part of the asteroid belt—objects in the asteroid belt often have the OC composition.
But the Chicxulub asteroid appears to stray from this pattern. Sediment samples taken from sites around the extinction event suggest the asteroid had a carbonaceous chondrite composition, described in the study as "quite rare." The space rock is also thought to have come from the outer half of the main asteroid belt.
The paper, titled "Dark primitive asteroids account for a large share of K/Pg-scale impacts on the Earth" is due to be published in the journal Icarus. A pre-print version was uploaded to the arXiv document hub on July 7.
Nesvorný added: "This work will help us better understand the nature of the Chicxulub impact, while also telling us where other large impactors from Earth's deep past might have originated."
