In 2005, Congress tasked NASA with finding "city killer" asteroids. In order to reach that goal, scientists are sending a telescope into space.
There could be a catastrophic threat lurking in space right now. We might not know until it's too late.
Near Earth, there are likely more than 25,000 asteroids large enough to level a city, according to recent estimates from NASA. Congress in 2005 tasked the space agency with finding 90 percent of these objects by 2020.
So far, scientists have only found about 11,500, less than half. The rest of these so-called "city killers" are what keep Dr. Kelly Fast up at night.
"Small stuff is hitting us all the time, so we're not so much worried about that. And we're not so worried about the large ones from the movies because we know where they are," Fast, the acting planetary defense officer at NASA, said at a conference in Arizona, the Daily Star reported. "It's the ones in between, about 140 meters and larger, that could really do regional rather than global damage and we don't know where they are."
The good news is that the chances of a dangerous asteroid hurtling towards Earth are relatively low, experts said. But scientists are gearing up for a mission decades in the making that will help us know for sure.
"You can't do anything about the asteroids if you don't know where they are," said Nancy Chabot, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory.
Why asteroids the size of football fields are so hard to spot
Scientists have been able to spot a potentially problematic asteroid years before it could threaten Earth. In late 2024, an asteroid was discovered with a record-high chance of hitting Earth in 2032, though those odds quickly fell to a number so low it might as well be zero.
But sometimes, scientists don't see asteroids coming until they enter our planet's atmosphere, said Katie Kumamoto, leader of planetary defense work at Lawrence Livermore National Laboratory, pointing to a 2013 incident in Russia. An asteroid the size of a house exploded over the city of Chelyabinsk with the force of 440,000 tons of TNT, damaging buildings and injuring more than 1,600 people, according to NASA.
"Due to the asteroid's approach from the daytime sky, it was not detected prior to impact, serving as a reminder that while there are no known asteroid threats to Earth for the next century, an Earth impact by an unknown asteroid could occur at any time," NASA said.
Kumamoto said that although potentially hazardous asteroids are bigger than a football field, they can be difficult to spot because they are relatively small and dark objects moving quickly in the vast expanse of space. Some asteroids can also be hidden by the glare of sunlight, making it easy for Earth-bound telescopes to miss them, according to NASA.
"It's certainly the largest threat in planetary defense, right?" said Kumamoto. "Everything about all of our mitigation strategies, they all depend on us having a long warning time."
New telescope will give us a 'big leg up'
To give us that warning, scientists are sending a telescope into space that can spot these asteroids well before they approach Earth. "Right now, construction is going fast and furious," said Amy Mainzer, the leader of the mission.
The telescope, known as the Near-Earth Object Surveyor, will detect infrared light or heat being emitted by elusive asteroids and comets. NEO Surveyor will be able to spot 140-meter asteroids that are about as far away as the Earth is from the Sun -- much further than telescopes can currently see, said Mainzer, who is also a professor at the University of California, Los Angeles.
"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.
The mission, which Mainzer said she first proposed in 2006, will launch in September 2027 on a SpaceX Falcon 9 rocket from Florida, according to NASA.
Mainzer said the goal is to find at least two-thirds of the potentially hazardous asteroids near Earth within five years. NASA expects the NEO Surveyor will find 90% of them within 10 to 12 years, fulfilling the space agency's congressional mandate.
The telescope will also thoroughly catalogue smaller objects because even they can do damage, Mainzer said. If something looks like it's headed our way, she said the NEO Surveyor can stop its search and focus on the threat.
"That will give us a leg up," she said. "A big leg up."
Chances of a city-killer hitting Earth are still low
Though it's obviously a concern that we don't yet have eyes on all the asteroids big enough to do serious damage, Chabot said the chances one of those asteroids is headed our way right now, unbeknownst to us, is low.
"Something that's about 140 meters in size is a very rare event. It's about every 20,000 years statistically speaking," she said. "So, your probability is not very high that that is going to happen tomorrow, but your probability's not very high that you're going to win the lottery either."
The hope -- enshrined in the NEO Surveyor's unofficial mission patch, which features a dinosaur roaring at an asteroid hurtling towards Earth -- is that the planet will "never again" experience such devastation.
"If the dinosaurs had a space program, maybe they'd still be here," Mainzer joked.