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NASA Warns: 15,000 'City Killer' Asteroids Remain Undetected

2/20/2026

Summary

Story summary

NASA experts warn that mid-sized asteroids, called "city killers," pose a growing threat.
At the American Association for the Advancement of Science (AAAS) meeting, Dr. Kelly Fast said about 15,000 asteroids 140 meters and larger remain undetected.
Current technology struggles to locate these objects, especially sunward approaches.
The DART mission showed deflection is possible.
The upcoming NEO Surveyor telescope aims to improve detection, but funding and planetary-defense preparedness remain critical.

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Story summary

NASA experts warn that mid-sized asteroids, called "city killers," pose a growing threat.
At the American Association for the Advancement of Science (AAAS) meeting, Dr. Kelly Fast said about 15,000 asteroids 140 meters and larger remain undetected.
Current technology struggles to locate these objects, especially sunward approaches.
The DART mission showed deflection is possible.
The upcoming NEO Surveyor telescope aims to improve detection, but funding and planetary-defense preparedness remain critical.