When we talk about planetary defense, especially in the context of the DART mission, mass extinction events – such as the Chicxulub impact – tend to come up in conversation. That particular event involved an impactor about ten kilometers in diameter which left a crater 180 kilometers across. Not only did the dinosaurs die off, other global effects included atmospheric heating, forest fires, acid rain… basically global devastation. Hence the importance of the DART mission.

It’s easy to focus on that one single event as being a reason to work toward planetary defense, but Chicxulub was by far not the only impact or even the largest. That designation goes to the Vredefort crater in South Africa, which up until recently, was thought to have been formed by an object measuring 15 kilometers in diameter. Now, in a new paper published in the Journal of Geophysical Research: Planets and led by Natalie Allen, computer simulations based on new geological evidence have upped that estimate to between 20 and 25 kilometers.

Estimating the size of the original crater and therefore the size of the impactor is a difficult process due to the erosive properties of our planet. The crater is two billion years old, and that is a lot of erosion to account for. The new evidence supports an original size of 250 to 280 kilometers, and the simulations show that the object had to have been traveling at 15 to 20 kilometers per second to leave such a huge crater.

Upon impact, dust and aerosols would have spread in the atmosphere, blocking sunlight. As for what was living on Earth at that time, co-author Miki Nakajima explains: Unlike the Chicxulub impact, the Vredefort impact did not leave a record of mass extinction or forest fires given that there were only single-cell lifeforms and no trees existed two billion years ago; however, the impact would have affected the global climate potentially more extensively than the Chicxulub impact did.

On top of there not being a lot of biological evidence of the Vredefort impact, the locations of landmasses two billion years ago would have been vastly different. Error bars on just what that looked like get larger the farther back in geologic time simulations go, but this new research could provide a better understanding of the makeup of the ejecta and how far it might have traveled after the initial impact. Finding that ejecta around the world would make it easier to create a more precise picture of the Earth at the time.

Once again, we remind you that there are presently no known asteroids greater than 140 meters in size that are known to be a threat to Earth for at least 100 years. All of the research into craters and asteroids helps us understand the potential threats that are out there and what effects they could have on our world.

More Information

University of Rochester press release

“A Revision of the Formation Conditions of the Vredefort Crater,” Natalie H. Allen et al., August 2022 8, Journal of Geophysical Research: Planets