An asteroid that could level a city now has a 3.1-per cent chance of striking Earth in 2032, according to Nasa data released on Tuesday – making it the most threatening space rock ever recorded by modern forecasting. Despite the rising odds, experts say there is no need for alarm. The global astronomical community is closely monitoring the situation and the James Webb Space Telescope is set to fix its gaze on the object, known as 2024 YR4, next month. “I’m not panicking,” said Bruce Betts, chief scientist for the non-profit Planetary Society. “Naturally when you see the percentages go up, it doesn’t make you feel warm and fuzzy and good,” he added, but explained that as astronomers gather more data, the probability is likely to edge up before rapidly dropping to zero. 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 and 90 metres (130 and 300 feet) 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 per cent. Since then, the figure has fluctuated but continues to trend upwards. Nasa’s latest calculations estimate the impact probability at 3.1 per cent, 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 30 metres in size posed such a significant risk was Apophis in 2004, when it briefly had a 2.7 per cent 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 per cent. “It’s a very, very rare event,” he said, 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 per cent, 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”, Moissl said. Unlike the 10km-wide (six-mile-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 40,000 miles per hour if it hits. If it enters Earth’s atmosphere, the most likely scenario is an airburst, meaning it would explode mid-air with a force of around 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, Betts said. 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.