A senior NASA planetary defence official has warned that thousands of undetected asteroids capable of wiping out entire cities may be passing near Earth, and humanity currently has limited means to stop them.
Speaking at the American Association for the Advancement of Science (AAAS) conference in Phoenix, Kelly Fast said the greatest concern is not the massive, extinction-level asteroids, which are largely tracked, nor the small rocks that regularly burn up in Earth’s atmosphere.
Instead, it is mid-sized asteroids, roughly 500 feet wide, that pose the most troubling risk.
She explained the gravity of the situation by saying it “keeps me up at night”.
Often referred to as “city killers,” these objects are large enough to cause significant regional devastation but small and dark enough to evade detection.
Fast estimates there could be around 25,000 such near-Earth objects, with only about 40 percent currently identified. Many are difficult to spot because they travel alongside Earth’s orbit, reflecting little sunlight even when observed with advanced telescopes.
NASA to launch near-Earth object surveyor next year
To address this blind spot, NASA plans to launch the Near-Earth Object Surveyor space telescope next year.
The mission will use thermal imaging to detect dark asteroids and comets that optical systems may miss. Fast described the effort as critical to ensuring scientists can “find asteroids before they find us.”
However, detection is only part of the challenge. While NASA successfully demonstrated asteroid deflection in 2022 through the DART mission, which deliberately crashed a spacecraft into the asteroid Dimorphos to alter its orbit, experts caution that replicating such an effort on short notice would be difficult.
Scientist says no asteroid deflection craft is ready for emergency
Nancy Chabot, a planetary scientist involved in the DART mission, noted that space agencies do not have deflection spacecraft “ready to go” if a city-sized asteroid were suddenly detected.
She also highlighted funding constraints that limit the ability to maintain planetary defense systems on standby.
The need for preparedness has again come into focus in the wake of talks about the asteroid YR4, which has a small chance of hitting the Moon in 2032, according to scientists.
Though the chances are small, some extreme measures have been proposed by experts, which include nuclear defense plans.