Asteroid's chance of hitting Earth in 2032 not high after all

New observations of a small asteroid discovered in December have led astronomers to conclude that the chances of it striking Earth are almost zero, after earlier data had indicated a higher risk of a collision with this space rock about 40 to 90 metres wide.

The asteroid — called 2024 YR4 — is orbiting on a path that will bring it close to Earth in 2032, with scientists previously calculating impact probability at around three per cent, the highest value ever recorded for such an object.

The new data, obtained by the European Southern Observatory's Chile-based Very Large Telescope and other facilities, gave a more precise picture of the asteroid's future trajectory. The impact probability has been lowered to 0.001 per cent, according to the European Space Agency's Near-Earth Objects Coordination Centre, while NASA's Jet Propulsion Laboratory put it at 0.004 per cent.

"The risk is plummeting," said Olivier Hainaut, an astronomer with the European Southern Observatory in Germany.

NASA put the probability of the asteroid striking the moon at 1.7 per cent.

The asteroid has been closely monitored since its discovery because of the potential threat it poses. An impact potentially could cause regional devastation and significant loss of life.

"An object 10 metres across would create an impact with the same energy as the Hiroshima bomb," said Hainaut, who estimated that an impact by YR4 would be 500 times more energetic than that.

"Fortunately, it is very likely that most of that energy would be dumped in the high atmosphere when the asteroid comes in. Still, it is a pretty big blast that could damage a city-wide area," Hainaut added.

Asteroids have struck Earth occasionally over its long history, often with cataclysmic results. For example, an asteroid estimated at 10 to 15 kilometres wide — much larger than 2024 YR4 — hit off the coast of Mexico's Yucatan Peninsula 66 million years ago, eradicating about three-quarters of the world's species and ending the age of dinosaurs.

NASA in 2022 carried out a proof-of-principle planetary defence mission by using its robotic DART spacecraft to change the trajectory of the asteroid Dimorphos, with an eye toward doing this in the future if one appears on a collision course with Earth.

Astronomers are learning more and more about asteroids. For instance, NASA's robotic OSIRIS-REx spacecraft journeyed to an asteroid named Bennu and, in 2020, collected samples of rock and dust that bore some of the chemical building blocks of life, according to a study published in January.

Another study estimated the potential damage that would be caused if an asteroid the size of Bennu — with a diameter of roughly 500 metres — strikes Earth. Scientists have estimated a one-in-2,700 chance of a Bennu collision with Earth in 2182.

Aside from the immediate devastation, researchers estimated an impact by a Bennu-sized asteroid would inject 100 million to 400 million tonnes of dust into the atmosphere, causing disruptions in climate, atmospheric chemistry and global photosynthesis lasting three to four years.