Odds of ‘city killer’ asteroid hitting Earth increase again
2024 YR4 was first detected on December 27 last year by the El Sauce Observatory in Chile.
Astronomers estimate its size to be between 40 to 90m wide, based on its brightness. Analysis of its light signatures suggests it has a fairly typical composition, rather than being a rare metal-rich asteroid.
The International Asteroid Warning Network (IAWN), a worldwide planetary defence collaboration, issued a warning memo on January 29 after the impact probability had crossed 1%. Since then, the figure has fluctuated but continues to trend upward.
Nasa’s latest calculations estimate the impact probability at 3.1%, with a potential Earth impact date of December 22, 2032.
That translates to odds of one in 32 – roughly the same as correctly guessing the outcome of five consecutive coin tosses.
The last time an asteroid of greater than 30m in size posed such a significant risk was Apophis in 2004, when it briefly had a 2.7% chance of striking Earth in 2029 – a possibility later ruled out by additional observations.
Surpassing that threshold is “historic”, said Richard Moissl, head of the European Space Agency’s planetary defence office, which puts the risk slightly lower at 2.8%.
Webb observations in March
“It’s a very, very rare event,” he told AFP, but added: “This is not a crisis at this point in time. This is not the dinosaur killer. This is not the planet killer. This is at most dangerous for a city.”
Data from the Webb telescope – the most powerful space observatory – will be key in better understanding its trajectory, said the Planetary Society’s Betts.
“Webb is able to see things that are very, very dim,” he said – which is key because the asteroid’s orbit is currently taking it out towards Jupiter, and its next close approach will not be until 2028.
If the risk rises over 10%, IAWN would issue a formal warning, leading to a “recommendation for all UN members who have territories in potentially threatened areas to start terrestrial preparedness,” explained Moissl.
Unlike the 10km-wide asteroid that wiped out the dinosaurs 66 million years ago, 2024 YR4 is classified as a “city killer” – not a global catastrophe, but still capable of causing significant destruction.
Its potential devastation comes less from its size and more from its velocity, which could be nearly 64,000km/h if it hits.
If it enters Earth’s atmosphere, the most likely scenario is an airburst, meaning it would explode midair with a force of approximately eight megatons of TNT – more than 500 times the power of the Hiroshima bomb.
But an impact crater cannot be ruled out if the size is closer to the higher end of estimates, said Betts.
The potential impact corridor spans the eastern Pacific, northern South America, the Atlantic, Africa, the Arabian Peninsula and South Asia – though Moissl emphasised it is far too early for people to consider drastic decisions like relocation.
The good news: there’s ample time to act.
Nasa’s 2022 DART mission proved that spacecraft can successfully alter an asteroid’s path, and scientists have theorised other methods, such as using lasers to create thrust by vaporising part of the surface, pulling it off course with a spacecraft’s gravity, or even using nuclear explosions as a last resort.
– Agence France-Presse
