A team of planetary scientists at the Southwest Research Institute have combined computer models of asteroid development with observations of known asteroids in order to determine the frequency of Chicxulub events.
Ankylosaurus magniventris, a large armored dinosaur species, witnesses the impact of an asteroid, falling on the Yucatan peninsula 66 million years ago. Image credit: Fabio Manucci.
At the end of the Cretaceous period, about 66 million years ago, a 10-km impactor crashed into Earth near the site of the small town of Chicxulub in what is now Mexico.
The impact unleashed an incredible amount of climate-changing gases into the atmosphere, triggering a chain of events that led to the extinction of non-avian dinosaurs and 75% of life on the planet.
Over the past several decades, much was learned about Chicxulub, but each advance has brought new questions.
“Two crucial questions remain unanswered: “What was the source?’ and “How often did such impacts occur on Earth in past times?” Dr. William Bottke is co-author of this study.
The Chicxulub Impactor was very similar to the meteorite class carbonaceous chondrite, which are some of the most beautiful materials in the Solar System.
Curiously, although carbonaceous chondrites can be found in many large bodies approaching the Earth, they are not nearly as common as the ones needed to cause the Chicxulub Impact with any reasonable probability.
” We decided to search for the Chicxulub siblings,” Dr. David Nesvorny said, the lead author of this study.
The researchers used computer models to track how objects escape from the main asteroid Belt, which is a region of small bodies between Jupiter and Mars.
Over eons, thermal force allows these objects to drift into dynamical escape hatches where the gravitational kicks from the planets can push them towards Earth’s orbit.
Using NASA’s Pleaides Supercomputer, they followed 130,000 model asteroids evolving in this slow, steady manner for hundreds of millions of years.
Particular attention was paid to asteroids found in the outer half the asteroid belt. This is the area that is farthest from the Sun.
To their surprise, the scientists found that 10-km-wide asteroids from this region strike the Earth at least 10 times more often than previously calculated.
” This result is fascinating not only because large numbers of carbonaceous-chondrite impactors are found in the outer half the asteroid belt, but also because simulations by the team can reproduce large asteroids orbits on the verge approaching Earth,” Dr. Simone Marchi, coauthor of the study, said.
” Our explanation of the Chicxulub’s source fits perfectly with what we know about how asteroids develop .”
Overall, the authors found that 10-km-wide asteroids hit the Earth once every 250 million years on average, a timescale that yields reasonable odds that the Chicxulub crater occurred 66 million years ago.
Moreover, almost half of the impacts were made from carbonaceouschondrites. This is a good match to what we know about the Chicxulub Impactor.
” This work will allow us to better understand the Chicxulub impact and also tell us where other large impactors of Earth’s deep history might have originated,” Dr. Nesvorny stated.
The findings appear in the journal Icarus.
David Nesvorny et al. 2021. A large proportion of K/Pg-scale Earth impacts are caused by dark primitive asteroids. Icarus 368: 114621; doi: 10.1016/j.icarus.2021. 114621