Will Asteroid Bennu Collide with Earth? Expectations of Massive Destruction on Our Planet

The rocky body called Bennu is classified as a near-Earth asteroid and is currently at its closest approach to Earth, which it reaches every six years, at a distance of 299,000 kilometers.

The asteroid could come even closer in the future, and scientists estimate that it has a one-in-2,700 chance of hitting Earth in September 2182. So what would happen if Bennu did collide with our planet? Well, it wouldn't be pretty, according to new research that used computer simulations of an asteroid about 500 meters in diameter like Bennu.

In addition to the immediate devastation, the study estimated that such an impact could release between 100 and 400 million tons of dust into the atmosphere, causing disruptions to the world's climate, atmospheric chemistry and plant photosynthesis lasting three to four years.

“The sun dimming caused by dust could cause an abrupt global ‘winter effect’ of reduced sunlight and colder temperatures,” said Lan Dai, a researcher at the IBS Center for Climate Physics at Pusan National University in South Korea and lead author of the study published this week in the journal Science Advances.

In the worst-case scenario, the researchers found, Earth's average surface temperature would drop by about four degrees Celsius, average rainfall would fall by 15 percent, plant photosynthesis would shrink by 20 to 30 percent, and the ozone layer that protects the planet from harmful solar ultraviolet radiation would shrink by about 32 percent.

The researchers said that a collision of an object the size of Bennu, a medium-sized asteroid, with the Earth's surface could generate a powerful shock wave, earthquakes, forest fires and thermal radiation, leave a large crater and throw huge amounts of debris upward.

Large amounts of aerosols and gases will reach the upper atmosphere, causing years-long impacts on climate and ecosystems, said Dai and another lead author, Axel Timmermann, a climate physicist and director of the IBS Centre for Climate Physics. The unfavorable climate conditions could prevent plants from growing on land and in the seas, they added.

An asteroid impact of this size could cause massive human casualties, but quantifying that number was beyond the scope of the study. The potential death toll “depends largely on where the asteroid hits,” Day said.

Scientists know a lot about Bennu, a loose jumble of rocky material rather than a solid body. It is the rocky remnant of a larger celestial body that formed near the dawn of the solar system about 4.5 billion years ago. NASA’s robotic spacecraft OSIRIS-REx is set to fly by Bennu in 2020 and collect rock and dust samples for analysis.

"The probability of an asteroid the size of Bennu hitting Earth is very small, 0.037 percent," Timmermann said. "Despite its small size, the potential impact would be very serious, and would likely lead to massive long-term food insecurity on our planet."