Astronomers have been tracking asteroid 2024 YR4 since its discovery late last year, watching its collision odds with Earth rise and then fall as new data came in. The one remaining question was whether it posed a threat to the moon.
That question now has an answer. Observations collected on Feb. 18 and Feb. 26 using the James Webb Space Telescope‘s infrared instruments have allowed NASA astronomers to refine the asteroid’s trajectory with enough precision to drop the probability of a lunar impact from 4.3% to zero, according to a March 5 NASA statement.
The asteroid will not hit the moon. It will, however, pass within 13,200 miles (21,200 kilometers) of the lunar surface — closer than some artificial satellites orbit Earth.
A Detection at the Edge of What’s Possible
Getting this data was not straightforward. Since spring of 2025, 2024 YR4 has been unobservable from both ground-based and space-based observatories, with one exception: JWST. Even then, the announcement says, the observations pushed the telescope to its limits. NASA officials described the resulting images as “among the faintest ever observations of an asteroid” in history.
The European Space Agency, which co-manages JWST alongside NASA and the Canadian Space Agency, framed the difficulty plainly in a separate statement: “To use one of the most complex machines humankind has ever built to track an almost invisible object many millions of kilometres away — and then accurately predict its position almost seven years into the future.”
The asteroid itself measures between 174 and 220 feet (53 to 67 meters) in diameter, roughly as wide as the Leaning Tower of Pisa is tall. An object that size striking Earth could devastate an entire city, releasing energy equivalent to 500 Hiroshima bombs, according to the report. That potential destructive force is what earned it the “city killer” label.
How the Numbers Shifted
2024 YR4 was first detected by the Asteroid Terrestrial-impact Last Alert System (ATLAS) network in late 2024. Early trajectory data produced something unprecedented in asteroid monitoring: a peak Earth-impact probability of 3.1%, the highest odds ever recorded for a potential asteroid collision. Those odds were subsequently reduced to zero by a combination of JWST data and observations from other telescopes, while the lunar impact probability held at 4.3% until this latest round of observations.
With both figures now at zero, the asteroid’s 2032 close approach will see it pass Earth by hundreds of thousands of miles, according to NASA.
The next step, as stated in the NASA announcement, is that the space rock will continue on its orbital path, with its 2032 flyby now fully characterized by the JWST data.
Photo by Tara Winstead on Pexels
This article is a curated summary based on third-party sources. Source: Read the original article
