The asteroid NASA is about to strike poses no threat to Earth, but 60% of city-killer rocks fly under the radar

• NASA is about to slam a spacecraft into an asteroid to nudge it into a new orbit.
• The Double Asteroid Redirection Test (DART) is practice for deflecting an asteroid away from Earth.

NASA is about to slam a spacecraft into an asteroid, obliterating the probe and nudging the space rock.

The Double Asteroid Redirection Test (DART) is aiming for an asteroid called Dimorphos, which is orbiting a giant asteroid called Didymos. By crashing into it, NASA hopes to push the smaller space rock into a new orbit closer to its parent asteroid. The impact, scheduled for Monday, is practice for deflecting dangerous asteroids away from our planet.

Dimorphos is 163 meters (535 feet) wide — big enough to obliterate a city like New York. That's no cause for concern, since it isn't on an Earth-bound trajectory, and DART won't change its path through the solar system. But that makes it perfect practice for one of the biggest threats in our cosmic neighborhood: city-killer asteroids, clocking in at 140 meters (460 feet) or larger.

Having a tried-and-true deflection method won't help protect Earth from asteroids if nobody sees them coming, though. Experts previously told Insider that NASA would need five to 10 years to build and launch a customized mission to deflect an incoming asteroid. To date, scientists have only identified 40% of city-killer asteroids orbiting near Earth, NASA estimates. Nobody knows where the rest of them are, or where they're going.

"Of course, you can't use any mitigation techniques unless you know where the asteroids are," Amy Mainzer, an astronomer at the University of Arizona, told Insider.

In 2005, Congress mandated that NASA catalogue 90% of those 140-meter-plus asteroids. Mainzer has been working on a space telescope called Near-Earth Object (NEO) Surveyor, which is designed to fulfill that goal.

"This is one of the long list of risks that are out there to life on our planet," Mainzer said. "It's something we should just go cross off our list of worries. And the way we do that, is we go look for the asteroids, in my opinion."

NEO Surveyor has made slow progress, though, and it just took another big hit.

At the beginning of 2022, the mission got an infusion of $143.2 million to propel it toward launch. But NASA has since rescinded $33 million of that budget for this year, according to Mainzer, and slashed the project's budget by $100 million for 2023. NASA estimates that will delay the telescope at least two years, so it will launch in 2028 at the earliest.

"We are obviously disappointed about the budget cuts, because we know that it creates a less efficient project. It's going to make it cost more and take longer," Mainzer said.

Smaller asteroids are already sneaking up on us

Asteroids have already surprised humans a few times in recent years.

In 2013, a house-sized asteroid screamed into the skies above Chelyabinsk, Russia, and exploded. The blast sent out a shock wave that broke windows, damaged buildings, and injured more than 1,400 people. No one on Earth saw it coming. That same day, a larger asteroid came within 17,000 miles of the planet.

Jim Bridenstine, who served as the Trump administration's NASA administrator, said in 2019 that the agency's modeling suggested an event like the Chelyabinsk meteor occurs about every 60 years.

But the Chelyabinsk rock was small — about 50 feet wide. In 2019, a 427-foot, "city-killer" space rock flew within 45,000 miles of Earth, and NASA had almost no warning about that either.

Then in 2020, an asteroid the size of a car passed closer to Earth than any known space rock had ever come without crashing. It missed our planet by about 1,830 miles. Astronomers didn't know the asteroid existed until about six hours after it whizzed by. Nobody saw it coming, because it was approaching from the direction of the sun.

Telescopes on the ground can only observe the sky at night, which means they miss almost everything that flies at us from the sun. NEO Surveyor, from its perch in Earth's orbit, would be able to spot such space rocks. Since it would use infrared light, it could also spot asteroids that are too dark for Earth-based telescopes.

The asteroid-spying telescope is suffering further delays

Mainzer first submitted the idea for an asteroid-hunting space telescope in 2006. NASA declined to take it on as a mission, funding other projects instead. She submitted proposals in 2010 and 2015 as well, but the agency kept passing.

NEO Surveyor finally became an official NASA mission in 2019. Then the project languished in what NASA calls "Phase A" — a stage focusing on design and technology development. Last year, NEO Surveyor passed a key review and moved into Phase B, allowing Mainzer and her team to start building prototypes and developing hardware and software.

Then Congress and President Joe Biden approved a budget of $143.2 million for the telescope in 2022 (later chopped to $110 million). That's a significant increase from the $28 million the mission received in 2021, and it allowed the team to make "significant" progress in all elements of the telescope's design, Mainzer said. But the agency's 2023 budget proposal allots just $40 million to the project.

Once in orbit, NEO Surveyor is expected to spend 10 years boosting NASA's catalogue from 40% of city-killing asteroids up to 90%. After that, researchers can move on to smaller classes of asteroid, like the one that shocked Chelyabinsk.

"If you do a good thorough search, you might find that there are no potentially hazardous objects on the impact trajectory. And that would be great," Mainzer said. "It's reasonably straightforward to go find out the answer, so we should go do that."

If the DART impact goes according to plan on Monday, NASA will be better equipped to divert any Earth-bound asteroid NEO Surveyor might discover.

September 23, 2022: This story has been updated to reflect the budget cut for NASA's Near-Earth Object Surveyor project.