15 miles across – asteroid that formed Earth’s largest crater, larger than previously thought

University of Rochester researchers have created a more accurate simulation of the impact that created Vredefort Crater two billion years ago.

An impactor raced toward Earth about two billion years ago, crashing into the planet not far from present-day Johannesburg, South Africa. The impactor, most likely an asteroid, created what is now the largest crater on Earth. Based on previous research, it is widely accepted by scientists that Vredefort Crater was created by an object about 15 kilometers (about 9.3 miles) in diameter and traveling at 15 kilometers per second.

However, a recent study from the University of Rochester suggests the impactor may have been significantly larger, which would have had catastrophic effects across the planet. This study, recently published in the Journal of Geophysical Researchimproves our understanding of massive impact and paves the way for more realistic simulations of impact events that have occurred on Earth and other planets, both in the past and in the future.

“Understanding the largest impact structure we have on Earth is critical,” says Natalie Allen ’20, now Ph.D. Student at Johns Hopkins University. Allen is the first author of the article, which is based on research she did as a student at Rochester with Miki Nakajima, an assistant professor of earth and environmental sciences. “Having access to the information provided by a structure like Vredefort Crater is a great opportunity to test our model and understanding of the geological evidence so we can better understand the impacts on Earth and beyond.”

An impactor — most likely an asteroid — raced toward Earth about two billion years ago and crashed into the planet near present-day Johannesburg, South Africa. The impactor formed the Vredefort crater, the largest crater on our planet today. Using updated simulation data, University of Rochester researchers discovered that the impact body that shaped Vredefort Crater was much larger than previously thought. Photo Credit: NASA Earth Observatory Image by Lauren Dauphin / University of Rochester Illustration by Julia Joshpe

Updated simulations point to “devastating” consequences

The Vredefort crater has eroded over a period of two billion years. For this reason, it is difficult for scientists to determine the exact size of the crater at the time of the original impact, and therefore the size and speed of the impactor that created the crater.

A crater 172 kilometers (107 miles) in diameter would be created by an object 15 kilometers (9.3 miles) across and moving at a speed of 15 kilometers (9.3 miles) per second. However, this is significantly smaller than the current estimates of the Vredefort crater. Based on new geological evidence and measurements, scientists estimate that the structure’s original diameter at the time of impact would have been between 250 and 280 kilometers (155 and 174 miles).

Allen, Nakajima and their colleagues ran simulations to adjust for the crater’s updated size. Their results showed that an impactor would have to be much larger – about 20 to 25 kilometers (12.5 to 15.5 miles) – and moving at a speed of 15 to 20 kilometers (9.3 to 12.4 miles) per second would have to move to explain a crater 250 kilometers deep.

That means the impactor that formed Vredefort Crater would have been larger than the asteroid that killed the dinosaurs and formed Chicxulub Crater 66 million years ago. These impacts have had detrimental effects around the world, including warming of greenhouses, widespread wildfires,

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