An artist’s impression of an asteroid.Credit: ESA-Science Office
The latest calculations indicate that the asteroid known as 2024 YR4 is much less likely to hit Earth than earlier measurements had suggested. Late on 19 February, telescope observations of the object allowed researchers to revise down the estimated chance of impact in 2032 from 3.1% — the greatest such threat ever recorded — to a still-worrying 1.5%.
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This value is likely to fall even further, to less than 1%, says Richard Moissl, head of the European Space Agency’s Planetary Defence Office, based in Frascati, Italy. As data floods in, uncertainty regarding 2024 YR4’s ‘impact corridor’ — the path it will take in the vicinity of Earth — is shrinking. If, as the uncertainty in an asteroid’s path gets smaller, Earth’s orbit remains within it, the likelihood of impact grows — which is why, earlier this week, space agencies reported that the risk had climbed. But now Earth is on the fringes of this region and edging out.
YR4 has given researchers their first chance to test an international protocol for responding to such hazards, put in place after the Chelyabinsk meteor hit Earth in 2013 without any warning. And with new asteroid-hunting telescopes coming online all the time, astronomers are likely to see many more close calls, says Moissl. “It’s not if, it’s when.”
Impact warning
Asteroids appear on researchers’ radars all the time — but not ones like YR4. It was first spotted in late December, and by 27 January, the object’s likelihood of hitting Earth had crept up above 1%, which triggered the United Nations-mandated International Asteroid Warning Network (IAWN) to spring into action.
IAWN’s network of researchers have been working overtime to precisely calculate the asteroid’s speed and path, says Moissl. They hope to report an impact risk of below 1% before April, when YR4’s orbit will take it beyond the range of ground-based telescopes until 2028.
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IAWN’s regular practice exercises, using hypothetical asteroids, have taught scientists to focus on quickly obtaining the most important measurements in real time — those that allow them to pinpoint when and where an asteroid could hit, and the damage it could cause, says Vishnu Reddy, a planetary scientist at the University of Arizona in Tucson and manager of IAWN.
This kind of rapid applied science is already familiar to meteorologists and seismologists, he says. “You have to coordinate and understand that you’re doing science to save the world, for the lack of a better term,” he says.
