NASA Warns of Untrackable ‘City-Killer’ Asteroids

Humanity remains largely defenseless against thousands of potentially catastrophic asteroids, according to Kelly Speedy, NASA’s Planetary Defense Officer. These “city-killer” asteroids, estimated to number around 15,000, are difficult to detect due to their size and orbital patterns, posing a significant threat to urban centers worldwide.

The Hidden Threat: What Makes These Asteroids So Dangerous?

While NASA tracks larger asteroids that could cause global devastation, and monitors the constant stream of smaller space rocks that burn up in the atmosphere, a critical gap exists in our knowledge of mid-sized asteroids. Fast highlighted that asteroids roughly 500 feet (140 meters) in diameter are particularly concerning. These asteroids are large enough to inflict substantial regional damage, potentially leveling a city, but small enough to evade current detection methods.

Approximately 25,000 of these asteroids orbit near Earth, but currently, only about 40% have been located. Their proximity to the sun, combined with their orbital path, makes them difficult to spot as they don’t reflect sunlight effectively, even with the most powerful telescopes.

Past Efforts and Current Limitations

NASA demonstrated the potential for asteroid deflection with the 2022 DART (Double Asteroid Redirection Test) mission, successfully altering the orbit of the asteroid Dimorphos. However, replicating this success with a “city-killer” asteroid presents significant challenges. Nancy Chabot, leader of the DART mission, emphasized the lack of readily available deflection technology and dedicated funding for such an endeavor.

The asteroid YR4, which briefly carried a 3.2% chance of impacting Earth in 2032, illustrates this vulnerability. While the probability was later reduced to near zero, the incident underscored the fact that, at present, humanity lacks the capability to actively deflect a threatening asteroid of this size.

The NEO Surveyor Mission: A Future Solution?

To address this critical gap in planetary defense, NASA plans to launch the Near-Earth Object (NEO) Surveyor space telescope in 2027. This telescope will utilize thermal signatures to detect dark asteroids and comets previously hidden from view. The goal is to identify at least 90% of asteroids larger than 140 meters within the next decade.

However, experts caution that simply finding these asteroids is not enough. Sustained funding and the development of robust defense technologies are crucial to effectively mitigate the risk posed by these “city-killer” asteroids.