WASHINGTON—Bennu, a rocky object classified as a near-Earth asteroid, is currently making its closest approach to Earth every six years at a distance of about 186,000 miles. Scientists estimate a one-in-2,700 chance of a collision with Earth in September 2182, potentially bringing it even closer.
If Bennu were to strike our planet, the consequences would be severe, according to new research based on computer simulations of an impact by an asteroid similar in size to Bennu, with a diameter of approximately three-tenths of a mile.
Aside from the immediate devastation, such an impact could inject 100–400 million tons of dust into the atmosphere, leading to disruptions in climate, atmospheric chemistry, and global photosynthesis lasting three to four years.
“The solar dimming caused by the dust would result in a sudden global ‘impact winter,’ characterized by reduced sunlight, lower temperatures, and decreased precipitation at the surface,” said 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 published in the journal Science Advances.
In a worst-case scenario, the research indicates that Earth’s average surface temperature could decrease by approximately 7 degrees Fahrenheit (4 degrees Celsius), rainfall could decrease by 15 percent, plant photosynthesis could be reduced by up to 20–30 percent, and the planet’s ozone layer could experience a 32 percent depletion, leaving it vulnerable to harmful solar ultraviolet radiation.
If a Bennu-sized object were to impact Earth’s land surface, it would generate a powerful shockwave, earthquakes, wildfires, thermal radiation, create a massive crater, and eject large amounts of debris into the atmosphere, according to the researchers.
Significant quantities of aerosols and gases would reach the upper atmosphere, leading to long-term effects on climate and ecosystems, as explained by Dai and study senior author Axel Timmermann, a climate physicist and ICCP director.
This mosaic image of asteroid Bennu, composed of 12 PolyCam images collected by the OSIRIS-REx spacecraft from a range of 15 miles on Dec. 2, 2018. NASA/Goddard/University of Arizona/Handout via Reuters
The adverse climate conditions resulting from the impact would hinder plant growth on both land and in the ocean, the researchers noted.
“Unlike the rapid decline and slow recovery of terrestrial plants, ocean plankton would recover within six months—and potentially thrive with remarkable diatom blooms triggered by iron-rich dust entering the ocean,” Dai added.
The researchers also highlighted severe ozone depletion in the stratosphere—the second layer of the atmosphere—as a consequence of the strong warming caused by the solar absorption of dust particles.
While a collision with an asteroid of this magnitude could lead to significant loss of human life, the study did not delve into the specifics of this calculation. Dai mentioned that the potential death toll would “largely depend on the location of the asteroid impact.”
Scientists have gathered substantial knowledge about Bennu, which is considered a “rubble pile” asteroid—a loose collection of rocky material rather than a solid entity. It is a rocky remnant of a larger celestial body that formed near the beginning of the solar system approximately 4.5 billion years ago. NASA’s OSIRIS-REx spacecraft traveled to Bennu and collected samples of rock and dust for analysis in 2020.
Earlier research published in January indicated that samples from Bennu contained some of the chemical building blocks essential for life, providing strong evidence that asteroids may have delivered the raw materials that facilitated the emergence of life on Earth.
Throughout Earth’s history, asteroids have occasionally collided with the planet, often resulting in catastrophic outcomes. One such event occurred 66 million years ago when an asteroid estimated to be 6–9 miles wide struck off the coast of Mexico’s Yucatan Peninsula, leading to the extinction of approximately three-quarters of the world’s species.
In 2022, NASA conducted a planetary defense mission as a proof of concept by using its robotic DART spacecraft to alter the trajectory of the asteroid Dimorphos, with the intention of employing similar strategies in the future if an asteroid is on a collision course with Earth.
“The probability of a Bennu-sized asteroid impacting Earth is quite low at 0.037%. Despite its low likelihood, the potential impact would be severe and could result in significant long-term food shortages and climate conditions comparable to some of the most massive volcanic eruptions in the past 100,000 years,” Timmermann emphasized.
“Therefore, it is crucial to assess the risk,” Timmermann concluded.
