Asteroid 2024 YR4 crossed a 1 percent impact probability threshold on January 27, 2025, prompting the International Asteroid Warning Network to issue its first-ever formal notification to the United Nations two days later. The object has since been cleared as an Earth threat for its December 22, 2032 close approach.
When astronomers first calculated the trajectory of a newly identified space rock in late January 2025, the numbers crossed a boundary that had sat dormant for more than a decade. Three independent orbit-computation centers agreed that the probability of an Earth impact for asteroid 2024 YR4 had surpassed 1 percent, triggering an international planetary-defense protocol that had never before been activated in real-world conditions. On 29 January, the International Asteroid Warning Network sent a formal notice to the United Nations Office for Outer Space Affairs and the Space Mission Planning Advisory Group. It was the first formal asteroid notification issued through an international planetary-defence system created more than a decade earlier. The warning did not predict that impact was the likely outcome, as its 1.3 per cent estimate meant there was still a 98.7 per cent chance of a miss.
How a Short Observation Arc Created an Impact Corridor
The NASA-funded Asteroid Terrestrial-impact Last Alert System discovered 2024 YR4 from its station at Río Hurtado, Chile, on December 27, 2024, two days after the asteroid had passed relatively close to Earth. Pre-discovery images extended the tracking record back only to December 25, giving researchers a very short segment of an orbit to project forward nearly eight years to December 22, 2032.
Early orbit predictions do not trace a single line through space. Instead, they produce a range of statistically possible trajectories often shown as a long uncertainty region. At first, only a tiny fraction of that region intersected Earth. As subsequent measurements narrowed the range of possible positions, Earth remained inside it. Because the denominator shrank around the planet, the calculated impact probability rose even though the asteroid itself did not alter its course.
Escalating Probabilities and the Torino Scale
Different computation centers and space agencies reported fluctuating risk figures as observation data evolved. NASA’s Center for Near-Earth Object Studies chronology says the estimate passed 1 per cent on January 27. On Tuesday, Nasa put the impact probability at 3.1 per cent, the highest ever recorded for an object of its size, up from 2.6 percent the previous week. Other tracking metrics noted the probability of a collision had increased to 2.3 percent (1 in 43), up from 1.2 percent, while NASA separately stated the odds were 1 in 32. Space rock 2024 YR4 was estimated by NASA to be 130 to 300 feet wide (40 to 100 metres), with other reports describing it at around 54 metres in diameter, about the size of New York’s Statue of Liberty or London’s Big Ben.
Along with these probability shifts, the object reached level 3 on the Torino Scale, a rating that calls for attention from astronomers. Space research organizations like NASA and the European Space Agency investigated potential ways to divert it, such as nuclear weapons, though scientists acknowledged that tracking the asteroid’s orbit after May would become increasingly difficult and that previous missions like NASA’s Dart cost roughly $325 million. Meanwhile, a 3D artist named Alvaro Gracia Montoya created an animation showing the devastating effect of an asteroid strike that went viral on social media.
Despite public fear sparked by viral videos, experts insisted there was no need to panic. Bruce Betts from the Planetary Society remains unconcerned. I'm not panicking,
he told AFP this week, explaining that further observations should refine the asteroid’s path and that with more data, the risk could drop to zero.
Activating the International Warning Protocol
What changed was that the risk had become large enough, for an object of this size, to activate an agreed process for observations, government notification and possible mission planning. On January 29, 2025, the International Asteroid Warning Network issued a formal notice to the United Nations Office for Outer Space Affairs and the Space Mission Planning Advisory Group. The notification identified a predicted impact risk corridor
stretching across the eastern Pacific Ocean, northern South America, the Atlantic Ocean, Africa, the Arabian Sea, and South Asia. Scientists noted that if the asteroid hits, it could cause severe blast damage
as far as 50 km (31 miles) from the impact site. The asteroid could potentially collide with Earth at a speed of 38,000 mph, delivering a blow comparable to that from 100 atomic bombs.
Clearance of the Threat and Planetary Defense Lessons
The asteroid was later cleared as an Earth threat, and a lingering lunar-impact possibility—estimated by NASA at a tiny 0.8 percent chance or 0.3 percent chance in various updates—was also eliminated in 2026. That outcome does not make the warning a false alarm, but rather shows what a warning system is supposed to do when the first calculation is incomplete. Further studies will continue to refine trajectories, reinforcing why the science of planetary defense requires international cooperation.
