![\"Asteroid](\"https:\/\/www.newsbeep.com\/ca\/wp-content\/uploads\/2026\/02\/asteroid-bennu-ejecting-particles-credit-nasa-wikimedia-commons-pd.jpg\")
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Asteroid Bennu ejecting particles. Credit: NASA \/ Wikimedia Commons<\/a> \/ Public domain<\/a><\/p>\n A hidden population of asteroids capable of destroying an entire city remains one of the biggest unresolved threats to Earth, according to NASA, planetary defense experts who say thousands of these objects have yet to be detected.<\/p>\n Kelly Fast, a planetary defense officer at NASA<\/a>, warned that the most dangerous asteroids are not the massive ones that could end life on Earth. Scientists already know where those objects are and track them closely. Smaller rocks also pose little risk, as most burn up harmlessly in the atmosphere.<\/p>\n The greater concern, Fast said, lies in a middle category that often escapes attention.<\/p>\n The danger of so-called \u201ccity killers\u201d<\/p>\n Speaking at a meeting of the American Association for the Advancement of Science in Phoenix, Arizona, Fast said researchers estimate that up to 15,000 near-Earth asteroids remain undiscovered. These objects are large enough to cause catastrophic damage on the ground but small enough to evade current detection systems.<\/p>\n Often referred to as \u201ccity killers,\u201d these asteroids typically measure a few hundred feet across. An impact of that size would not trigger a global extinction, but it could flatten a major city, ignite fires, and disrupt infrastructure across a wide region.<\/p>\n \u201cWhat keeps me up at night is the asteroids we don\u2019t know about,\u201d Fast said, according to reports from the meeting.<\/p>\n Why are many asteroids hard to spot<\/p>\n Fast said these mid-sized asteroids<\/a> are difficult to detect because of both their size and their position in space. Many travel along paths close to Earth\u2019s orbit around the Sun, where they reflect little sunlight toward Earth-based telescopes.<\/p>\n<\/p>\n Even advanced observatories struggle to detect objects approaching from the Sun\u2019s direction, leaving scientists with limited warning if one were headed toward the planet.<\/p>\n A new telescope aims to close the gap<\/p>\n To address that blind spot, scientists are preparing a space-based solution. NASA plans to launch the Near-Earth Object Surveyor next year.<\/p>\n Unlike traditional telescopes that rely on visible light, the mission will search for heat. Asteroids and comets emit thermal energy as they warm in space, making them visible in infrared wavelengths even if they appear dark through optical instruments.<\/p>\n Researchers say the telescope could uncover thousands of previously hidden objects and give authorities years of warning instead of days.<\/p>\n A successful test, but no ready defense<\/p>\n Detection alone, however, does not mean an asteroid can be stopped. In 2022, NASA conducted a landmark planetary defense experiment called DART. The mission deliberately crashed a spacecraft into Dimorphos, a small moon<\/a> orbiting a larger asteroid, at roughly 14,000 miles per hour.<\/p>\n The impact altered Dimorphos\u2019 orbit, marking the first time humans had intentionally changed the path of a natural object in space. Scientists described the test as a critical proof of concept.<\/p>\n Experts warn preparedness remains limited<\/p>\n