NASA Warns of 15,000 Undetected ‘City-Killer’ Asteroids Threatening Earth
- A chilling assessment from a NASA scientist reveals that Earth faces a significant, largely unaddressed threat from near-Earth asteroids.
- Fast articulated her anxieties, stating, “What keeps me up at night is the asteroids we don’t know about.” This isn’t a worry about the massive, well-tracked asteroids –...
- The challenge stems from their size and orbital characteristics.
A chilling assessment from a NASA scientist reveals that Earth faces a significant, largely unaddressed threat from near-Earth asteroids. While much attention is given to the potential for catastrophic impacts from very large asteroids, the real concern, according to planetary defense officer Kelly Fast, lies with a population of roughly 15,000 “city-killer” asteroids that remain undetected. These asteroids, approximately 500 feet in diameter, are large enough to inflict devastating regional damage but small enough to evade current detection systems.
Fast articulated her anxieties, stating, “What keeps me up at night is the asteroids we don’t know about.” This isn’t a worry about the massive, well-tracked asteroids – their trajectories are known. Nor is it the constant stream of tiny space rocks that burn up harmlessly in Earth’s atmosphere. It’s the mid-sized asteroids that pose the greatest risk, precisely because they are difficult to find.
The challenge stems from their size and orbital characteristics. According to Fast, We find an estimated 25,000 near-Earth asteroids of this size (140 meters or larger), yet current surveys have only identified around 40% of them. These asteroids are small enough to be missed by existing telescopes and their proximity to the sun makes detection even harder. They essentially blend into the background, reflecting minimal sunlight as they orbit alongside Earth.
The potential consequences of an impact from one of these “city-killers” are severe. While not globally catastrophic, an impact could level a major metropolitan area, causing widespread destruction and loss of life. The term “regional damage” accurately reflects the scale of devastation such an event could unleash.
NASA is actively working to address this blind spot. Plans are underway to launch the Near-Earth Object Surveyor space telescope next year. This new telescope will employ a different detection method, utilizing thermal signatures to identify dark asteroids and comets that are currently invisible to optical telescopes. By detecting the heat emitted by these objects, the Surveyor aims to significantly improve our catalog of potentially hazardous near-Earth objects.
However, detection is only half the battle. Even if we identify these asteroids, humanity currently lacks the capability to deflect them. Nancy Chabot, leader of NASA’s Double Asteroid Redirection Test (DART) mission, emphasized this point. “We would not have any way to go and actively deflect one right now.”
The DART mission, successfully completed in , demonstrated that This proves possible to alter the trajectory of an asteroid by intentionally colliding with it. A spacecraft was deliberately crashed into Dimorphos, a small moon orbiting the asteroid Didymos, at a speed of 14,000 miles per hour. The impact successfully changed Dimorphos’s orbital period. However, Chabot cautioned that replicating this feat with a “city-killer” asteroid would be far more challenging, as there are currently no dedicated deflection spacecraft “sitting around ready to go.”
The financial hurdles to maintaining a constant planetary defense capability are also significant. Chabot noted that space agencies currently lack the funding to keep deflection systems on standby, suggesting that a proactive defense posture is not currently prioritized. “We could be prepared for this threat. We could be in very good shape. We need to take those steps to do it,” she stated.
These concerns are heightened by the recent attention on asteroid YR4, discovered in , which currently has a 4% chance of impacting Earth in . While this particular asteroid is being closely monitored, it underscores the broader vulnerability to undetected threats. The situation highlights a critical gap in our planetary defense infrastructure – the ability to both identify and mitigate the risk posed by these potentially devastating “city-killer” asteroids.
The challenge isn’t simply a matter of technological development; it’s also a question of political will and resource allocation. Addressing this threat requires sustained investment in detection capabilities, deflection technologies, and a commitment to proactive planetary defense strategies. The warning from NASA’s Kelly Fast serves as a stark reminder that the threat from space is real, and that preparation is not merely prudent, but essential.