For a brief few weeks in early 2025, astronomers were worried about the asteroid 2024 YR4.
Discovered in late 2024 by an automated telescope in Chile as part of the Asteroid Terrestrial-Impact Last Alert System (ATLAS) sky survey, it’s a not only a near-Earth asteroid but one that astronomers feared could get too close for comfort to our fair planet and pose a potential impact risk. At 60 or so meters in diameter, 2024 YR4 wouldn’t cause global damage if it fell to Earth, but it would explode upon impact with the energy of an eight-megaton bomb, so local damage would be considerable. Thus, astronomers were right: it was something to worry about.
Initial observations indicated the asteroid might hit Earth on December 22, 2032. Calculating the trajectory of an asteroid is tricky, and the further ahead the prediction goes, the fuzzier the numbers get. By mid-February 2025, astronomers had refined that Earth-impact probability to around 3 percent, which wasn’t high but was still somewhat concerning.
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Happily, follow-up observations tightened the uncertainties in the projected orbit, effectively ruling out a late-2032 impact.
They ruled out an Earth impact, that is. Amazingly, a chance remains that 2024 YR4 will hit the moon!
As it stands now, the chance of a lunar impact on December 22, 2032, is actually higher than the mid-February probability of the asteroid hitting Earth on that date: about 4 percent. That’s still small but not zero.
If 2024 YR4 does whack into our lone natural satellite, what will happen? Is Earth (or, more to the point, those of us who live on it) in any danger? In a preprint paper accepted for publication in the Astrophysical Journal Letters, astronomers investigated the potential fallout. The answer they got is reassuring—mostly.
Given the uncertainties in the asteroid’s exact trajectory, the scientists found that—if the asteroid were to hit at all—its chance of striking the moon’s near side would be around 86 percent, meaning we’d likely get a good view of the fireworks. If so, Earth-based observers could see a brief flash as 2024 YR4’s immense kinetic energy—its energy of motion—would convert into light and heat, though it’s difficult to…
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