Asteroid Bennu could trigger a global winter lasting more than 3 years and here’s what’s known

At the latest count there were more or less 1.5 million asteroids and minor planets which have been identified, named and numbered in our solar system. The vast majority can be found in the asteroid belt, orbiting the Sun between Mars and Jupiter.

Asteroid approaches happen every day while close approaches with Earth and near misses are less frequent but inevitable. The Center for Near-Earth Object Studies (CNEOS) tracks the orbits of asteroids and computes the chances of them impacting Earth.

2025 CZ1 a small asteroid the size of a family car will come within 195,000 miles of Earth today, 7 February. 2016 CO248, which is a similar size to a school bus, is further out - 3.21 million miles is the closest it will get to us here on planet Earth.

How big is the asteroid Bennu and what is it made of?

The CNEOS is more concerned with other asteroids such as Bennu which is classified as a medium-sized Near Earth Asteroid (NEA). Bennu passes close to Earth every six years, coming within 186,000 miles (299,000 kilometers). A carbon-rich, rock asteroid about one-third of a mile wide (about the same height as the Empire State Building), Bennu formed around 1 to 2 billion years ago.

Originally named 1999 RQ36, it was renamed in 2013. Bennu is an ancient Egyptian deity linked with the Sun, creation, and rebirth.

A report published in Science Advances journal this week looks at the chances that Bennu could strike Earth and the consequences of such an impact. There is an estimated 0.037% possibility that Bennu will collide with Earth in September 2182.

The reports explains how such a collision would launch 400 million tons of dust into the stratosphere. This is turn, would produce “marked disruptions in climate, atmospheric chemistry, and global photosynthesis”.

What would happen if a medium-sized asteroid collided with Earth?

The impact would cause regional to large-scale devastation and long-lasting climatic effects. The gases, dust and aerosols in the atmosphere would block out the sun’s rays causing global mean temperatures to drop by 4°C, plunging the planet into an “impact winter”.

Earth would also lose around 32 percent of the Ozone layer that protects us from ultraviolet radiation.

Such an event likely triggered the Cretaceous–Paleogene event approximately 66 million years ago which caused the mass extinction of three-quarters of the plant and animal species on Earth.

The impact winter would last between two to three years, having serious repercussions for those on tierra firme but with less of an effect on marine life. The study indicates that marine plankton growth would behave differently, recovering within six months and even increasing to levels above normal.

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