Scientists estimate that there are thousands of asteroids large enough to destroy cities near Earth. Although there are no known immediate threats, NASA plans to help track down these elusive asteroids.
Scientists work to discover ‘city killer’ asteroid before impact
In 2005, Congress tasked NASA with finding an “urban killer” asteroid. To achieve that goal, scientists are sending telescopes into space.
There are potentially devastating threats lurking in space right now. We may not know until it’s too late.
According to recent estimates from NASA, there could be more than 25,000 asteroids near Earth large enough to flatten cities. Congress in 2005 ordered space agencies to discover 90 percent of these objects by 2020.
So far, scientists have discovered only about 11,500, less than half of them. The rest of the so-called “urban killers” are what keep Dr. Kelly Fast up at night.
“We don’t worry too much about the little ones because they’re hitting us all the time. And the big ones in the movie, we don’t worry as much because we know where they are,” Fast, NASA’s acting planetary defense officer, said at a conference in Arizona, the Daily Star reported. “Those in between, about 400 feet or more, could actually cause damage locally, not globally, and we don’t know where they are.”
The good news is that the chances of a dangerous asteroid hurtling toward Earth are relatively low, experts say. But scientists have been preparing a mission for decades to help us know for sure.
“You can’t do anything about an asteroid if you don’t know where it is,” said Nancy Chabot, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory.
Why it’s hard to find asteroids the size of a soccer field
Scientists were able to discover a potentially troublesome asteroid years before it could threaten Earth. In late 2024, an asteroid was discovered that had the highest probability ever of colliding with Earth in 2032, but the probability quickly dropped to a value as low as zero.
But scientists sometimes don’t realize an asteroid is approaching until it enters the atmosphere, said Katie Kumamoto, a planetary defense research leader at Lawrence Livermore National Laboratory, citing an incident in Russia in 2013. An asteroid the size of a house exploded over the city of Chelyabinsk with a force of 440,000 tons of TNT, damaging buildings and injuring more than 1,600 people, according to NASA.
“The asteroid’s close approach in the daytime sky meant it was not detected before impact. This serves as a reminder that although there is no known asteroid threat to Earth for the next century, an unknown asteroid impact on Earth could occur at any time,” NASA said.
Kumamoto said potentially dangerous asteroids are larger than a soccer field but can be difficult to spot because they are relatively small, dark objects that move quickly through the vast expanse of space. Some asteroids can also be obscured by sunlight glare, making them easier to miss with Earth-based telescopes, NASA said.
“That’s certainly the biggest threat to planetary defense, right?” said Mr. Kumamoto. “All of our mitigation strategies are dependent on us having a long warning window.”
New telescope will bring us ‘huge progress’
To provide that warning, scientists are sending telescopes into space that can spot these asteroids long before they approach Earth. “Construction is progressing at a furious pace right now,” said mission leader Amy Mainser.
The telescope, known as the Near-Earth Object Surveyor, detects infrared radiation and heat emitted by elusive asteroids and comets. Meinser, who is also a professor at the University of California, Los Angeles, said NEO Surveyor will be able to find 140-meter asteroids that are about the same distance from the sun as Earth — much further than what can currently be seen with telescopes.
“The idea is that if you can spot them when they’re far away, you’ll probably be able to spot them years to decades earlier than when you get closer,” Mainzer said.
The mission, first proposed by Meinser in 2006, is scheduled to launch from Florida in September 2027 on a SpaceX Falcon 9 rocket, NASA said.
Mainzer said the goal is to discover at least two-thirds of potentially dangerous asteroids near Earth within five years. NASA expects the NEO Surveyor to discover 90% of them within 10 to 12 years, fulfilling the space agency’s Congressional mission.
Meinzer said the telescope will be thoroughly cataloged because even smaller objects can cause damage. If something appears to be headed toward us, the NEO Surveyor can stop searching and focus on the threat, she said.
“That would be an advantage for us,” she said. “I stepped up a lot.”
It is still unlikely that a city destroyer will attack Earth.
While it’s obviously a concern that we haven’t yet monitored all asteroids large enough to cause significant damage, it’s unlikely that one of those asteroids is now heading toward us without our knowledge, Chabot said.
“Something about 140 meters in size is a very rare event. Statistically speaking, it happens about once every 20,000 years,” she said. “So the odds of it happening tomorrow aren’t very high, but the odds of winning the lottery aren’t that high either.”
The hope embedded in NEO Surveyor’s unofficial mission patch, which features a dinosaur roaring at an asteroid hurtling towards Earth, is that Earth will “never again” experience such a devastation.
“If dinosaurs had a space program, they would probably still be here,” Mainzer joked.
