Could an asteroid hit the moon? NASA says chances have risen
A so-called "city killer" asteroid known as 2024 YR4 won't hit the Earth — but the moon might not be so lucky.
Astronomers and scientists previously expressed some concern that the asteroid could collide with Earth. After its discovery in late 2024, its odds of impact with Earth briefly rose to historically high levels at a 3.1% chance. Eventually, however, astronomers ruled out the threat.
While Earthlings may be safe, our latest glance of the asteroid in May, courtesy of NASA's James Webb Space Telescope, led the agency to conclude that YR4 now has an even higher chance of colliding with the moon in 2032 — though the chance still rests at only 4.3%
The asteroid has left our view as it orbits the sun, meaning that the May Webb observations were the last chance to observe YR4 until it reemerges in 2028. NASA already has plans to study it again in three years. Until then, here's what we know about 2024 YR4 and its possible impact to our moon.
Asteroid 2024 YR4 was estimated to measure between 174-220 feet, about the size of a 10-story building, according to NASA and the ESA.
As the nickname suggests, an asteroid of this size would, as Scientific American magazine put it, unleash "enough localized devastation to destroy any unlucky metropolis in the way," with immediate effects resembling a detonating hydrogen bomb.
Asteroid YR4 is a near-Earth asteroid, which NASA explained means it has an orbit that brings it into Earth's region of the solar system. As it was large enough to cause localized damage if it were to impact Earth, and surpassed the 1% impact probability threshold, it was of interest for planetary defense until the probability of impact was lowered.
For some time, YR4 was the only object among more than 37,000 known large space rocks with any chance of hitting Earth anytime soon. Though the probability was only 3.1%, this actually marked a record high. With new observations in February 2025, however, astronomers announced that the probability had lowered to only 0.28%.
Asteroid 2024 YR4 has a below 0.5% chance of hitting the Earth, according to observations from NASA and other astronomers.
Another asteroid, Aphophis, received some attention after its discovery in 2004, and the 2.7% chance it held of hitting Earth in 2029. Additional observations showed that, while it will make a close flyby, Apophis does not pose a risk.
While a collision with the Earth has now been ruled out, the moon is another story. Webb's March observations showed that the odds of YR4 colliding with the moon had risen from February from 1.7% to 3.8%. Odds rose again after Webb's May observations to 4.3%.
NASA assured the public, however, that the moon's orbit around the Earth would not be altered by a collision with an asteroid the size of YR4.
Eric Lagatta, USA TODAY NETWORK, contributed to this report.
Iris Seaton is the trending news reporter for the Asheville Citizen Times, part of the USA TODAY Network. Reach her at iseaton@citizentimes.com.
This article originally appeared on Asheville Citizen Times: What is a 'city killer' asteroid? NASA says asteroid may hit moon
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