‘City-Killer’ Asteroid has a Small—but Non-Zero—Risk of Striking Earth in 2032

A sizable “city-killer” asteroid that was discovered late last year has been calculated to have a one in 77 chance of striking the Earth just eight years from now, according to NASA’s Jet Propulsion Laboratory. Although the chance of impact is still very low, the object’s higher than one percent chance of impacting the planet has prompted NASA’s planetary defense office to designate the asteroid as an “object of concern,” ranking only second to the asteroid Apophis as a planetary threat.

First spotted on December 27, 2024, asteroid 2024 YR4 was discovered by Chile’s El Sauce Observatory. Its size falls somewhere between 40 and 90 meters (130 to 300 feet), a diameter somewhere between roughly one-half to a full football field’s length. While it came within a little over two lunar distances to the Earth mere days before it was first spotted, 2024 YR4 is estimated to have a 1.3 percent chance of impacting the planet on December 22, 2032.

These estimates were issued by the International Asteroid Warning Network (IAWN) in a January 29 memo. 2024 YR4 is ranked as a level 3 threat on the Torino Impact Hazard Scale, warranting special attention from astronomers due to the object’s greater than one percent chance of striking the Earth, along with its potential to cause “localized destruction.” The Torino Scale ranks potential impacts on a scale of zero to 10, with 10 indicating a guaranteed impact that could cause the end of civilization as we know it. The only object with a higher rating was 99942 Apophis, although the asteroid, named for the Egyptian god of darkness and disorder, was downgraded from its rating of four after it was found that it wouldn’t cross Earth’s path for over a century.

Although a potential strike by 2024 YR4 wouldn’t be nearly powerful enough to cause extinction-level devastation on the order of the Chicxulub impact that ushered in the end of the dinosaurs 66 million years ago, its size is similar to the object that exploded over Tunguska in 1908. According to estimates made by NASA’s Center for Near Earth Object Studies, the energy from an impact by 2024 YR4 would be similar to the detonation of a 7.9-megaton nuclear bomb, with destructive effects being felt as far away as 50 kilometers (30 miles) from the impact site.

Because of its short observation window there’s still a lot of uncertainty in regards to 2024  YR4’s orbit, and the object is expected to remain in view for only a few more months; observations will resume when it makes another close pass in 2028, possibly providing astronomers with enough data to nail down an accurate plot of the asteroid’s orbit.

“The first step in the planetary defence response is to trigger further observations,” according to University of Edinburgh professor of planetary astronomy Colin Snodgrass. “If these observations don’t rule out an impact, the next steps will be more detailed characterisation measurements using telescopes, and discussion of what space agencies could do in terms of more detailed reconnaissance and eventually mitigation missions. This asteroid is of the scale that a mission like Dart could be effective, if required, so we have the technology and it has been tested.”

“Most likely this one will pass by harmlessly,” Snodgrass added. “It just deserves a little more attention with telescopes until we can confirm that. The longer we follow its orbit, the more accurate our future predictions of its trajectory become.”