There Are 13,500 Asteroids That Could Level a City — NASA Has Only Found Half
Nobody panic. But also maybe read this.
Scientists estimate there are more than 25,000 asteroids near Earth large enough to level a city. Congress tasked NASA with finding 90 percent of them by 2020. So far they've found about 11,500 — less than half. The other 13,500 or so are just out there somewhere, untracked, doing whatever asteroids do.
The ones scientists lose sleep over aren't the mountain-sized rocks from disaster movies — those are mostly mapped. It's the middle ground that's the problem. Asteroids around 140 meters and larger, big enough to cause serious regional destruction, small enough to be hard to spot, and largely unaccounted for.
"It's the ones in between that could really do regional rather than global damage and we don't know where they are," said Dr. Kelly Fast, NASA's acting planetary defense officer.
Why They're So Hard to Find
A 140-meter asteroid is roughly the size of a football field. In space that's actually pretty small — a dark, fast-moving object against a vast black backdrop. Some hide in the glare of sunlight entirely, invisible to Earth-based telescopes no matter how sophisticated.
The 2013 Chelyabinsk incident is the example everyone points to. An asteroid the size of a house came in from the daytime sky — completely undetected — and exploded over a Russian city with the force of 440,000 tons of TNT. Over 1,600 people were injured. Buildings were damaged across the region. Nobody saw it coming because nobody could.
"An Earth impact by an unknown asteroid could occur at any time," NASA said in its own assessment of the incident.
Everything about planetary defense — every mitigation strategy humans have developed — depends on having enough warning time to actually do something. No warning, no options.
The Fix That's Coming
NASA is launching a space telescope called the Near-Earth Object Surveyor in September 2027 on a SpaceX Falcon 9 rocket from Florida. It detects infrared heat signatures from asteroids rather than relying on reflected sunlight — which means it can spot dark objects that ground-based telescopes routinely miss.
The telescope will be able to detect 140-meter asteroids as far away as the distance between Earth and the Sun — dramatically further than current capabilities. The goal is to find at least two-thirds of potentially hazardous asteroids within five years and 90 percent within 10 to 12 years, finally fulfilling that congressional mandate from 2005.
Mission leader Amy Mainzer first proposed the concept back in 2006. It's been a long road.
"The idea is, if we can spot them when they're far away, we'll probably spot them years to decades in advance of any close approach," Mainzer said. "That will give us a big leg up."
How Worried Should You Actually Be
Not very — at least not today. A 140-meter asteroid strike is statistically a once-every-20,000-years kind of event. The odds of one heading our way right now without anyone knowing are genuinely low.
"Your probability is not very high that that is going to happen tomorrow," said planetary scientist Nancy Chabot of Johns Hopkins. "But your probability's not very high that you're going to win the lottery either."
The whole point of the NEO Surveyor is to remove the uncertainty entirely. Right now we're operating with incomplete information on half the objects capable of serious damage. That's the part worth fixing — not because an impact is imminent but because detection is the only thing that makes any kind of response possible.
As Mainzer put it — if the dinosaurs had a space program, maybe they'd still be here.
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