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Remember Asteroid 2024 YR4? -- A New Update on Possible Lunar Impact [1]
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Date: 2025-04-04
About that space rock that looked for a few weeks earlier this year like it might have a non-negligible chance of colliding with the Earth on a return visit in 2032 — even though such a potentially devastating event has been ruled out to a 5-sigma* certainty for many weeks now, it turns out its chances of colliding with our Moon on Dec 22, 2032 has actually risen to 1/26 (3.8%).
From physics.org:
The asteroid, thought to be capable of leveling a city, set a new record in February for having the highest chance—3.1%—of hitting our home planet than scientists have ever measured. Earth's planetary defense community leapt into action and further observations quickly ruled out that the asteroid—called 2024 YR4—will strike Earth on December 22, 2032. But the odds that it will instead crash into Earth's satellite have been steadily rising. After the Webb telescope turned its powerful gaze towards the asteroid last month, the chance of a moon shot is now at 3.8%, NASA said. ... The new Webb data also shed light on the size of the space rock, which was previously estimated to be between 40 and 90 meters (131 to 295 feet). It is now believed to be 53 to 67 meters, roughly the height of a 15-story building. This is significant because it is bigger than the 50-meter threshold for activating planetary defense plans. If the asteroid still had a more than 1% chance of hitting Earth, "the development of one or more deflection missions would already be starting now", Moissl said. … While no one wanted to need to test Earth's defenses on the potentially hugely destructive asteroid 2024 YR4, many scientists are hoping it will strike the moon. "The possibility of getting a chance for an observation of a sizable moon impact is indeed an interesting scenario from a scientific point of view," Moissl said. It could offer up a range of information that would be "valuable for planetary defense purposes," he added.
The interesting thing here is that when the 3.1% chance of a collision with Earth was reached on February 18, there was also roughly a 1% chance of a lunar collision — but as the chance of a hit on our planet rapidly declined to near zero in the following weeks with additional observations, the possibility of an impact on the Moon nearly quadrupled to its present level of 3.8% instead of falling.
The current best model fit for the existing data (based on 476 separate observations, including those from the James Webb Space Telescope) suggest 2024 YR4’s nearest approach to the Earth in 2032 will still be 260,000 km (about 2/3 of the average distance to the Moon), with a 3-sigma uncertainty range of +/- 82,600 km.
When it comes to the Moon though, the asteroid is now expected to pass within just 1,400 km of the lunar surface (+/- a similar 3-sigma uncertainty range of 83,000 km). Definitely too close for comfort if NASA or anyone else is contemplating setting up a manned lunar base prior to 2032. OTOH, we should have more than sufficient data on its next relatively close approach in 2028 to determine with virtual certainty whether it will be a hit or a miss on December 22, 2032.
* Five-sigma certainty is the “gold standard” of scientific prediction, corresponding to a less than one-in-a-million chance of falling outside the range of uncertainty (0.00006%), in contrast to the more usual two-sigma (5%) or three-sigma (0.3%) standards.
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