Bennu, a near-Earth asteroid, is classified as a “rubble pile” object a loose collection of rocky materials rather than a solid mass. It currently makes its closest approach to Earth every six years, coming within about 186,000 miles (299,000 km). Scientists estimate there is a one-in-2,700 chance that Bennu could collide with Earth in September 2182.
If Bennu were to strike our planet, the consequences would be catastrophic. New research based on computer simulations has outlined the likely effects of such an impact, which would include immediate devastation and long-term global disruptions to climate, atmospheric chemistry, and photosynthesis. These disruptions could last for three to four years, according to the study published in the journal Science Advances.
Lan Dai, a postdoctoral research fellow at the IBS Center for Climate Physics (ICCP) at Pusan National University in South Korea and the lead author of the study, explained that a Bennu impact would release between 100 and 400 million tons of dust into the atmosphere. “The solar dimming due to dust would cause an abrupt global ‘impact winter’ characterized by reduced sunlight, cold temperatures, and decreased precipitation at the surface,” Dai said.
In the worst-case scenario, Earth’s average surface temperature could drop by about 7 degrees Fahrenheit (4 degrees Celsius), while rainfall could fall by 15%. The research also predicts a 20-30% reduction in plant photosynthesis and a 32% depletion of the ozone layer, which protects the planet from harmful ultraviolet (UV) radiation.
The impact would trigger powerful shockwaves, earthquakes, wildfires, and thermal radiation, leaving a massive crater and ejecting debris high into the atmosphere. Aerosols and gases released into the upper atmosphere would cause long-term climate and ecosystem effects, study senior author Axel Timmermann, a climate physicist and ICCP director, noted.
The unfavorable climate conditions would severely inhibit plant growth on land and in the ocean. While land-based plants would take around two years to recover, ocean plankton could rebound within six months due to iron-rich dust deposited in the water, which could trigger unprecedented algae blooms, Dai explained.
The researchers also highlighted severe ozone depletion in the stratosphere due to the warming effects of dust particles absorbing sunlight. This would lead to increased UV radiation reaching Earth’s surface, further stressing ecosystems and human health.
Although the study did not estimate potential human casualties from such an impact, Dai said the number of deaths would largely depend on where the asteroid struck. A collision in a densely populated area would be particularly devastating.
Bennu has been extensively studied, especially after NASA’s OSIRIS-REx spacecraft visited the asteroid in 2020 and collected samples for analysis. Earlier studies revealed that Bennu contains some of the chemical building blocks of life, supporting the idea that asteroids may have delivered the ingredients for life to early Earth.
Asteroids have hit Earth throughout its history, sometimes with catastrophic results. One such impact, estimated to have been caused by a 6-9 mile (10-15 km) wide asteroid, struck off the coast of Mexico’s Yucatán Peninsula 66 million years ago. That impact wiped out about three-quarters of Earth’s species, including the dinosaurs.
In 2022, NASA tested a planetary defense strategy by using its DART spacecraft to successfully alter the trajectory of the asteroid Dimorphos. This proof-of-concept mission demonstrated the possibility of changing the path of a potentially hazardous asteroid.
Timmermann emphasized the importance of considering Bennu’s risks despite its relatively low 0.037% likelihood of impact. “Even though small, the potential impact would be very serious and would likely lead to massive longer-term food insecurity on our planet and climate conditions that are similar to those seen only for some of the largest volcanic eruptions in the last 100,000 years,” he said.
“As rare as it may be, it’s crucial to think about the risk,” Timmermann added.