The near-Earth asteroid Bennu, classified as such due to its relatively close proximity to Earth, orbits our planet every six years, passing at a distance of approximately 299,000 kilometers (186,000 miles). While the current trajectory poses no immediate threat, scientists have calculated a small but non-zero probability – one in 2,700 – of a potential collision with Earth in September 2182.
This raises a crucial question: what would be the potential consequences of an impact by an asteroid of Bennu’s size, roughly 500 meters (three-tenths of a mile) in diameter? New research, based on extensive computer simulations, paints a concerning picture.
Beyond the immediate devastation caused by the impact itself, the study predicts significant long-term disruptions to Earth’s environment. The impact is estimated to inject a substantial amount of dust, ranging from 100 to 400 million tons, into the atmosphere.
This dust cloud would have profound consequences, including disruptions to climate patterns, alterations in atmospheric chemistry, and a significant decline in global photosynthesis, potentially lasting for three to four years.
“The solar dimming due to dust would cause an abrupt global ‘impact winter’ characterized by reduced sunlight, cold temperature 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 lead author of the study published this week in the journal Science Advances, opens new tab.
The researchers’ worst-case scenario projections reveal a significant decline in Earth’s average surface temperature, estimated at approximately 4 degrees Celsius (7 degrees Fahrenheit). Concurrently, average rainfall is predicted to decrease by 15%.
Furthermore, the study anticipates a substantial reduction in plant photosynthesis, ranging from 20% to 30%, and a concerning 32% depletion of the ozone layer, which plays a crucial role in shielding Earth from harmful solar ultraviolet radiation.
The impact of an asteroid of Bennu’s size – categorized as a medium-sized asteroid – on Earth’s land surface would have devastating consequences. This includes the generation of a powerful shockwave, triggering earthquakes, widespread wildfires, and the release of intense thermal radiation.
The impact would leave a massive crater and eject a colossal amount of debris into the atmosphere, according to Dai and study senior author Axel Timmermann, a climate physicist and director of the International Center for Climate and Environment (ICCP).
The researchers emphasize that the injection of large quantities of aerosols and gases into the upper atmosphere would have long-lasting repercussions on Earth’s climate and ecosystems, extending for several years. These unfavorable climatic conditions would severely hinder plant growth, both on land and in the oceans.
“In contrast to the rapid reduction and slow two-year-long recovery of plants on land, plankton in the ocean would recover within six months – and even increase afterwards with unprecedented diatom (a type of algae) blooms triggered by iron-rich dust deposition into the ocean,” Dai said.
The researchers attribute the severe ozone depletion in the stratosphere – the second layer of the atmosphere – to the significant warming caused by the absorption of solar radiation by the dust particles injected into the atmosphere.
While the study did not explicitly quantify the potential loss of human life, it is acknowledged that an asteroid impact of this magnitude would have catastrophic consequences. Dr. Dai emphasized that the extent of human casualties would largely depend on the specific location of the asteroid impact.
Bennu, classified as a “rubble pile” asteroid – a loosely bound collection of rocky material rather than a solid object – is a remnant from the early solar system, dating back approximately 4.5 billion years. NASA’s OSIRIS-REx spacecraft successfully collected samples of rock and dust from Bennu’s surface in 2020, providing valuable insights into the asteroid’s composition.
A study published in January revealed the presence of key chemical building blocks of life within these samples, strongly suggesting that asteroids may have played a crucial role in seeding early Earth with the essential ingredients for the emergence of life.
Throughout Earth’s history, asteroid impacts have occurred periodically, often with devastating consequences. A prime example is the asteroid estimated to be 10-15 kilometers (6-9 miles) wide that struck the Yucatan Peninsula in Mexico 66 million years ago, leading to the extinction of approximately three-quarters of all species on Earth, marking the end of the dinosaur age.
In 2022, NASA successfully demonstrated a planetary defense strategy through its DART mission. This mission involved intentionally crashing a spacecraft into the asteroid Dimorphos, successfully altering its trajectory.
This groundbreaking achievement paves the way for future planetary defense efforts, providing a crucial capability to deflect potentially hazardous asteroids that may pose a threat to Earth.
“The likelihood that a Bennu-sized asteroid will strike Earth is quite small at 0.037%. 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,” Timmermann said.
“So it is important to think about the risk,” Timmermann added.
