Earth At Risk? Thousands Of ‘City-Killer’ Asteroids Still Missing From NASA's Detection Radar

Last Updated:February 17, 2026, 08:30 IST

NASA warns 15,000 mid-sized "city-killer" asteroids remain undetected. DART proved asteroid deflection possible, but no spacecraft is ready.

Scientists still don’t know the location of thousands of potentially destructive “city-killer" asteroids, NASA’s head of planetary defence has said.

Speaking at the American Association for the Advancement of Science conference in Phoenix, Dr Kelly Fast said roughly 15,000 mid-sized near-Earth objects, at least 140 metres wide, are yet to be identified. An impact from one of these bodies in a populated region could cause significant regional devastation, she said.

“It’s really the asteroids that we don’t know about. We’re not so much worried about the large ones from the movies, because we know where they are, she said, according to a report in The Telegraph.

“And small stuff is hitting us all the time. [I’m] not so much worried about that. It’s the ones in-between that could do regional damage. Maybe not global consequences, but they could really cause damage…And we don’t know where they all are. It’s not something that even with the best telescope in the world you could find," she added.

Dr Nancy Chabot of Johns Hopkins University, who led NASA’s Double Asteroid Redirection Test (DART), warned there is currently no ready-to-launch spacecraft capable of deflecting a threatening asteroid. DART deliberately crashed a specially made spacecraft into a mini-moon called Dimorphos at 14,000mph to alter its orbit.

“Dart was a great demonstration. But we don’t have [another] sitting around ready to go if there was a threat that we needed to use it for," Dr Chabot said.

“If something like YR4 had been headed towards the Earth, we would not have any way to go and deflect it actively right now…We could be prepared for this threat. And I don’t see that investment being made," she added.

Concern intensified last year when asteroid YR4, roughly the size of a football pitch, was detected after passing Earth on Christmas Day 2024. Although later calculations ruled out a 2032 collision, scientists say the episode highlights gaps in detection efforts.

NASA’s upcoming Near-Earth Object Surveyor space telescope, expected to launch next year, aims to improve that record. Currently, the agency has identified only about 40 per cent of objects larger than 140 metres.

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