A NASA scientist has warned that thousands of city-killing asteroids could strike Earth, and there’s currently no defense humanity could use to stop them.

NASA expert Kelly Fast said the ‘city-killing’ asteroids could do regional damage

Kelly Fast, a planetary defense officer at NASA, expressed her fear of the 15,000 medium-sized asteroids that remain undetected but have the potential to wipe out a city due to their impact.

“What keeps me up at night is the asteroids we don’t know about. Small stuff is hitting us all the time so we’re not so much worried about that,” the Daily Star reported Fast said at the conference of the American Association for the Advancement of Science in Phoenix, adding, “And we’re not so worried about the large ones from the movies because we know where they are. It’s the ones in between, about 140 metres and larger, that could really do regional rather than global damage and we don’t know where they are.”

Fast said there are 25,000 space rocks near Earth, but NASA can only locate about 40% of them.

“It takes time to find them, even with the best telescopes.”

Could a new, state-of-the-art telescope detect the killer asteroids?

While telescopes are an effective tool for locating asteroids, the optical instruments may struggle to detect those that travel alongside Earth in its orbit around the sun. Most space rocks are easier to find when they reflect in the sunlight, Fast said, according to The Times.

The Near-Earth Object Surveyor space telescope, which will launch in late 2027, will use thermal signatures locate near-Earth objects and “will find asteroids and comets that other space missions cannot, filling a critical gap in humanity’s ability to detect potentially hazardous near-Earth objects,” according to information about the telescope on NASA’s website.

Fast said her primary role was to “find asteroids before they find us” and, if necessary, develop ways of “getting asteroids before they get us,” per The Times.

Details on previous asteroid sightings near Earth

It’s not the first time asteroids or comets have been feared to strike Earth. In February 2025, Blavity reported that NASA scientists were monitoring asteroid 2024 YR4.

Scientists at the Asteroid Terrestrial-impact Last Alert System in Río Hurtado, Chile, first discovered it on Dec. 27, 2024. The space rock, which measures around 130 to 300 feet, had a 98% chance of missing Earth on Dec. 22, 2032.

“An asteroid this size impacts Earth on average every few thousand years and could cause severe damage to a local region,” the European Space Agency stated at the time.

city-killing asteroids

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