NASA's James Webb telescope took an emergency look at the asteroid scientists feared would smash into Earth in 2032
News Bethan Finighan Science and Innovation Writer 09:42, 02 Apr 2025
The infamous "city-killer" asteroid has caught the attention of scientists again after emergency observations revealed where the space rock could smash into.
Asteroid 2024 YR4 once posed the greatest risk of impact to Earth in recorded history after astronomers revealed the space rock had a 3.1 per cent – or one-in-32- chance – of striking Earth on December 22, 2032.
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As experts gathered more and more data regarding the asteroid's path, its impact odds were downgraded to near zero in February this year.
Now, NASA's James Webb Space Telescope has revealed that impact is still a possibility – just not with Earth.
The space telescope confirmed that asteroid 2024 YR4 is no longer a hazard to Earth, with a zero chance the asteroid could smash into our home planet. However, a direct hit with the Moon is still possible.
"While an Earth impact by 2024 YR4 on December 22, 2032, has now been ruled out, it continues to have a non-zero probability of impacting the Moon at this time," astronomers revealed in a preliminary report.
The asteroid has a two per cent chance of slamming into the moon in 2032, co-author of the report Andrew Rivkin, an astronomer at Johns Hopkins University, told New Scientist.
The report comes after the powerful telescope completed the first of two planned observations of the asteroid.
Further observations by James Webb are planned for May 2025, before the asteroid disappears from view until 2028. These observations aim to "primarily help refine the orbital and thermal properties" of the asteroid, the authors wrote.
The recent observations aimed to determine the true size of the asteroid, which was previously estimated to be between 40 and 90 metres.
"In general, the brighter the asteroid, the larger it is, but this relationship strongly depends on how reflective the asteroid's surface is," the European Space Agency (ESA) wrote in a blog post on February 10.
"2024 YR4 could be 40 m [130 feet] across and very reflective, or 90 m [295 feet] across and not very reflective … the hazard represented by a 40 m asteroid is very different from that of a 90 m asteroid," it added.
NASA's space telescope watched the asteroid rotate once every 20 minutes over a five hour period on March 26. Scientists used data about its brightness, known distances and angles from the Sun to estimate that the space rock is around 60 m in diameter.
Experts had previously warned that the asteroid, dubbed the "city-killer", has the potential to do "serious damage" and wipe out a large city.
"Size and composition are big players in possible damage, along with impact location," David Rankin, Catalina Sky Survey engineer and asteroid hunter told Space.com. "While impact effects would be more localised than regional, it certainly has the potential to do serious damage to the area it hits," Rankin added.
It's not yet clear exactly what a direct hit with the Moon could do, but since the celestial body doesn't have an atmosphere that slows down asteroids and meteorites like the Earth does, the space rock could hit the lunar surface at full speed and create a permanent crater that is hundreds of metres wide.
The Moon is no stranger to being struck by huge lumps of space rock. In fact, research has shown that, nearly four billion years ago, asteroids carved out two Grand Canyon-sized craters on the far side of the Moon in less than 10 minutes.
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Some experts are even hoping for impact. "We've got our fingers crossed for a moon impact," Alan Fitzsimmons, a physics and math professor at Queen's University Belfast in the UK, who was not involved in the observations, told New Scientist. "It would have no effect on Earth, but would allow us to study the formation of a lunar crater by a known asteroid for the very first time."
