An asteroid with a tiny chance of striking Earth in 2032 is triggering planetary defense planning

• Asteroid 2024 YR4 has a 1.3% chance of impacting Earth in 2032, NASA reports.
• Astronomers all over the world are watching the asteroid, trying to narrow down its future path.
• The risk will likely drop to 0%, but if not, NASA may have to plan a mission to push the asteroid away.

An asteroid large enough to flatten a city may be on track to crash into Earth on December 22, 2032, but the odds are very small, NASA announced Wednesday.

"There should be no particular panic or great concern about this object," Davide Farnocchia, the technical lead at NASA's Center for Near-Earth Object Studies, told Business Insider.

Even so, the object — called asteroid 2024 YR4 — is Earth's biggest known impact threat in 20 years and it's already triggered international planetary-defense planning.

What's the threat level?

As of Thursday morning, the chance of a 2032 impact was 1.3%, or odds of 1 in 77.

As a result, two international asteroid-response groups are actively monitoring the situation: the International Asteroid Warning Network, chaired by NASA, and the Space Mission Planning Advisory Group, chaired by the European Space Agency.

SMPAG is meeting in Vienna next week. If the risk remains above 1%, the group "may begin to evaluate the different options for a spacecraft-based response," the ESA wrote in a Wednesday statement.

A telescope in Chile first discovered the asteroid in late December, but fresh January data drove its risk level past 1%.

That sounds low, but a risk above 1% is uncommon and, therefore, significant for asteroid watchers, Farnocchia said. "It just means that we pay close attention and do everything that we need to do to better understand the situation," he said.

As telescopes all over the planet gather more data on the asteroid, the odds of impact will likely change.

The last time this happened was with the discovery of asteroid Apophis in 2004. It briefly had a nearly 3% impact risk, but after further data narrowed down its future path, it proved to be no threat at all.

That's what NASA expects for 2024 YR4, saying it will probably rule out the possibility of impact by April.

April is the cutoff point because, after that, the asteroid will be too far away for telescopes to continue tracking its path. It won't be observable again until 2028.

If the risk is still above 1% in April, the world's space agencies may find themselves plotting the first-ever mission to deflect an incoming asteroid.

How big is asteroid 2024 YR4?

Asteroid 2024 YR4 is somewhere between 130 to 300 feet wide — not big enough to pose a global threat.

Richard Binzel, an MIT professor of planetary sciences, told BI that if it struck Earth, the effect would be similar to the Tunguska event that occurred in Siberia in 1908, when an asteroid or comet exploded as it plowed through the atmosphere.

The fireball and blast wave flattened 500,000 acres of forest — about 34 times the size of Manhattan.

It's too early to determine the exact location of a potential impact for 2024 YR4.

The asteroid's size and risk make it a 3 out of 10 on the Torino Scale, which categorizes potential impact threats, with 10 being a certain impact that threatens the future of civilization.

A rating of 3 means YR4 will likely prove to be a non-threat, but given the eight-year timeline, it deserves close attention.

"I like our chances," said Binzel, who invented the Torino Scale. He expects more incidents like this "as we're finding more and more of these objects."

How NASA could deflect an incoming asteroid

NASA has already practiced deflecting a dangerous asteroid.

The agency's DART mission in 2022 slammed into a small asteroid and pushed it into a different orbit around the larger asteroid it's circling. It was a test, and it showed the method works.

Binzel thinks eight years is enough warning time to organize a larger deflection mission for asteroid 2024 YR4, if necessary. Given the asteroid's size, it won't take as big of a punch to budge it as, say, the asteroid that killed the dinosaurs.

Failing that, there's always the possibility of evacuation for the affected area. Farnocchia said it's important to remember that Earth is mostly ocean, and then a lot of its land is uninhabited.

However, "it's a little too early to talk about that scenario because we have time now," he said. "The priority is getting observations and better understanding what the situation actually is."

The risk could increase before it drops

The risk could rise before it falls. If new data narrows down the asteroid's possible paths through space, but an Earth impact is still one of them, the risk of impact will be higher.

Even then, further data could completely remove Earth from the cone of probability. That's still the most likely outcome.

Asteroid hunters like Binzel have long fought to increase space surveillance enough to spot potentially dangerous asteroids. In that sense, the discovery of 2024 YR4 is a kind of victory.