On September 24, 2182, a relatively large space rock will hit the Earth’s surface with a probability of 0.037%. Although the probability of a collision is low, Bennu is still one of the most potentially dangerous known asteroids in our solar system, and we should be prepared for what could happen. A first-of-its-kind study has modeled the damage to the entire planet that could be caused by a possible Bennu impact, leading to a sudden onset of winter and global food shortages.
A group of researchers from South Korea has developed scenarios that show how the Earth’s climate and life on our planet would be affected by a collision with a medium-sized asteroid like Bennu. The team found that such a collision would cause massive destruction that could last up to three to four years. In the most intense scenario described by the team, several hundred million tons of dust would significantly reduce the amount of sunlight reaching the 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 the Earth’s climate after an asteroid impact, in the journal Science Advances.
Bennu is a relatively small near-Earth asteroid that approaches Earth about every six years. Scientists believe that 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 target of NASA‘s historic OSIRIS-REx mission, which captured a chunk of Bennu in October 2020 and dropped it to Earth in September 2023. The mission allowed scientists to examine the ancient stone up close, discovering that Bennu contains some of the most important building blocks of life.
A collision with Bennu would have been very destructive, but the Earth has seen worse. Around 66 million years ago, an asteroid about 6 miles (10 kilometers across) slammed into the Earth, killing most of its first inhabitants, including the dinosaurs. Compared to Bennu, which is about 0.3 miles (0.5 km) wide, the asteroid that killed the dinosaurs was massive. Medium-sized asteroids like Bennu are more common in the solar system.
Asteroids of medium size collide with Earth approximately every 100,000–200,000 years on average, said Axel Timmermann, director of the IBS Center for Climate Physics (ICCP) at Pusan National University in South Korea and co-author of the study, in an email. “This means that our early human ancestors may have already experienced some of these planet-altering events, potentially impacting human evolution and even our own genetic makeup.”
To determine the consequences of Bennu’s collision with our planet in 157 years, the authors of the study simulated an idealized scenario of a medium-sized asteroid impact on Earth—”idealized” is used here as a statistical term, as this scenario is obviously far from ideal.
The collision would eject between 100 and 400 million tons of dust into the upper layers of the atmosphere, affecting global climate, the chemical composition of the atmosphere, and the photosynthesis of terrestrial plants, as well as plankton in the ocean, the research team concluded.
The most dramatic consequence of an asteroid impact similar to Bennu would be the formation of a large amount of dust, which would cloud the atmosphere, leading to a dimming of sunlight. (Another research team proposed a similar scenario for the aftermath of the Chicxulub asteroid impact, which doomed the dinosaurs.)
According to the study, the dimming of the Sun could cause a global surface cooling of up to 7 degrees Fahrenheit (4 degrees Celsius), a 15% reduction in precipitation, and a significant depletion of the ozone layer by approximately 32%.
“Abrupt cooling will create unfavorable climatic conditions for plant growth, leading to an initial reduction in photosynthesis in terrestrial and marine ecosystems by 20–30%,” said Lan Dai, ICCP researcher and lead author of the study. “This is likely to result in a massive decline in photosynthesis levels. It will probably lead to widespread disruptions in global food security.”
But that’s not all the bad news. Under the ocean’s surface, iron from the asteroid could rise into the stratosphere after impact and settle in certain parts of Earth’s ocean, triggering an unprecedented bloom of silicate-rich algae. Ocean plankton would also recover approximately six months after the impact, compared to two to three years for terrestrial plants, and its growth rates would increase beyond pre-impact levels, according to the study.
“We were able to track this unexpected response to iron concentration in the dust,” said Timmermann. “The simulated excessive bloom of phytoplankton and zooplankton could be a blessing for the biosphere and might help mitigate the food security threat associated with the long-term decline in terrestrial productivity.”
No matter how unlikely Bennu’s impact may be, researchers are determined to put Earth’s fate in the hands of its inhabitants. NASA’s successful Double Asteroid Redirection Test (DART) in September 2022 proved humanity’s ability to alter an asteroid’s trajectory, an immeasurably important step in demonstrating our capability to protect the planet from rocky invaders from space.
Besides, there are more pressing matters. The recently discovered asteroid 2024 YR4 has a 1.9% probability (1 in 53) of colliding with Earth in 2032. Let’s hope that the team’s recent simulations never come to pass—whether due to luck or thanks to humanity’s ingenuity and determination in the face of a common threat.
