On September 24, 2182, a relatively large space rock has a 0.037% chance of crashing onto the surface of Earth. Although the chances of impact are slim, Bennu is still one of the most potentially hazardous known asteroids in our solar system, and we need to be prepared for what could come. A first-of-its-kind study simulated the planet-wide damage that would be caused by Bennu’s unlikely impact, leading to a sudden onset of winter and global food shortages.
A group of researchers based in South Korea drew up scenarios indicating how Earth’s climate and life on our planet would be affected by the impact of a medium-sized asteroid like Bennu. The team found that such an impact would cause massive disruptions that could last up to three or four years. In the most intense scenario the team described, several hundred million tons of dust would significantly reduce the sunlight that reaches Earth’s surface, causing temperatures to drop around the world and affecting how plants grow on Earth. The researchers published their study, which is the first to model Earth’s climate after an asteroid impact, in Science Advances.
Bennu is a relatively small near-Earth asteroid that makes a close pass to Earth every six years or so. Scientists believe the space rock may have broken off from a much larger carbon-rich asteroid about 700 million to 2 billion years ago and gradually drifted closer to Earth. The asteroid was the subject of a historic NASA mission, OSIRIS-REx, which snagged a piece of Bennu in October 2020 and dropped it off on Earth in September 2023. The mission allowed scientists to probe the ancient rock up-close, revealing that Bennu contains some of the crucial building blocks of life.
An impact from Bennu would be very destructive, but Earth has seen worse. Around 66 million years ago, an asteroid that was roughly 6 miles wide (10 kilometers across) struck Earth, killing most of its early inhabitants, including the dinosaurs. Compared to Bennu, which is about 0.3 miles (0.5 km) wide, the dinosaur-killing asteroid was massive. Medium-sized asteroids like Bennu are more common in the solar system.
A graphic showing the damage caused by asteroids of different sizes. Graphic: NASA“On average, medium-sized asteroids collide with Earth about every 100–200 thousand years,” Axel Timmermann, director of the IBS Center for Climate Physics (ICCP) at Pusan National University in South Korea, and co-author of the study, said in an emailed statement. “This means that our early human ancestors may have experienced some of these planet-shifting events before with potential impacts on human evolution and even our own genetic makeup.”
To determine the impact of Bennu striking our planet in 157 years from now, the study authors modeled an idealized collision scenario of a medium-sized asteroid on Earth—idealized being used here as a statistical term, as the scenario is obviously very far from ideal.
The collision would inject 100 million to 400 million tons of dust into the upper atmosphere, the team concluded, impacting the global climate, atmospheric chemistry, and photosynthesis of terrestrial plants, as well as plankton in the ocean.
The most dramatic outcome of a Bennu-like asteroid collision would be the voluminous amounts of dust that would cloud the atmosphere, resulting in the dimming of light from the Sun. (A different team posited a similar scenario for the aftermath of the Chicxulub asteroid impact that doomed the dinosaurs.)
The Sun’s dimming could cause global surface cooling of up to 7 degrees Fahrenheit (4 degrees Celsius), a 15% drop in rainfall, and severe depletion of the ozone layer by about 32%, according to the study.
“The abrupt impact winter would provide unfavorable climate conditions for plants to grow, leading to an initial 20–30% reduction of photosynthesis in terrestrial and marine ecosystems,” Lan Dai, a researcher at the ICCP and lead author of the study, said in a statement. “This would likely cause massive disruptions in global food security.”
It’s not all bad news, though. Beneath the surface of the ocean, iron from the asteroid could blast into the stratosphere following the impact and settle in parts of Earth’s oceans, triggering unprecedented blooms of silicate-rich algae. Plankton in the ocean would also recover around six months after the collision, as opposed to two to three years for terrestrial plants, and its growth rates would increase to higher levels compared to before the asteroid impact, according to the study.
“We were able to track this unexpected response to the iron concentration in the dust,” Timmermann said. “The simulated excessive phytoplankton and zooplankton blooms might be a blessing for the biosphere and may help alleviate emerging food insecurity related to the longer-lasting reduction in terrestrial productivity.”
Ejecta streaming from Dimorphos about a day after the DART impact. Image: NASA, ESA, STScI, J. Li (PSI)As unlikely as an impact from Bennu is, researchers are determined to put Earth’s fate firmly in Earthlings’ hands. NASA’s successful Double Asteroid Redirection Test (DART) in September 2022 proved humankind’s ability to change the trajectory of an asteroid, an immeasurably important step in proving out our ability to defend the planet from rocky interlopers from space.
And besides, there are more immediate fish to fry. The recently discovered asteroid 2024 YR4 has a 1.9% chance (1-in-53 odds) of impacting Earth in 2032. Hopefully, the recent team’s simulations never come to pass—if not thanks to luck, than to humankind’s ingenuity and determination in face of a common threat.
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