2024 YR4, the “city-killer” asteroid that briefly made headlines last year due to a small but non-zero chance that it may hit the Earth, may soon have increased odds of striking our Moon.
Asteroid 2024 YR4 was first discovered on December 27, 2024, by the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Chile. Initial observations showed around a 1 percent chance that it could collide with Earth on December 22, 2032, while follow-up observations of the asteroid briefly showed a slightly higher chance of the asteroid making an impact. At 3.1 percent, it briefly became considered the most dangerous space object since tracking began.
But pinning down the path of an object is a tricky business, requiring repeated observations. Thankfully, as often stated by astronomers during that slightly nervous time, as more observations came in, the chances of impact with Earth fell dramatically, and now stand so low they are basically zero. But the Moon may not be so lucky.
Following observations by JWST and analysis by NASA’s Center for Near-Earth Object Studies at the agency’s Jet Propulsion Laboratory (JPL) in Southern California, NASA has updated the chance of impact with the Moon on December 22, 2032, to 4.3 percent. On that date, it is currently predicted to pass within around 0.00007 astronomical units (AU) of the Moon, with 1 AU being the distance between the Earth and the Sun.
“The odds of an impact into the Moon have always been there. It’s been lower at that time because the Earth [was] a bigger target,” planetary scientist Dr Andrew Rivkin, from Johns Hopkins University in Maryland, told IFLScience back in April 2025.
“The way that the orbit improved made the position move away from the Earth, but it moved toward the Moon. So there’s like almost a 4 percent chance it’s going to hit the Moon. That means there’s a better than 96 percent chance it’s going to miss the Moon, but if it did hit the Moon, it really would be pretty spectacular!”
While an Earth impact was an intimidating prospect, astronomers are a bit more excited by the prospect of it slamming into our companion space rock. As Rivkin said, it would be pretty spectacular, potentially even causing a widespread meteor shower on Earth.
“It would be visible from Earth and there would even be new lunar meteorites that would arrive on Earth (nothing dangerous), but there is no guarantee,” Richard Moissl, the head of the European Space Agency’s Planetary Defence Office, told IFLScience back in February. “Definitely, a new observable moon crater would be the outcome!”
NASA stresses that the asteroid hitting the lunar surface would not alter the Moon’s orbit. However, a study led by Paul Wiegert, professor of physics at the University of Western Ontario, suggests that it could release around the equivalent of 6.5 megatons of TNT in energy, leaving the Moon with a crater around 1 kilometer (0.62 miles) in diameter.
“If 2024 YR4 strikes the Moon in 2032, it will (statistically speaking) be the largest impact in approximately 5,000 years,” the team explained in their paper. “We estimate that up to 108 kg of lunar material could be liberated in such an impact by exceeding lunar escape speed.”
Attempting to model various impacts, the team found that the ejected Moon debris could cause spectacular meteor showers on Earth. While this would be an amazing sight for the layperson, and meteorites making it to the surface of Earth is not ruled out, it could be a nightmare for any governments or organizations with satellites in orbit.
“The lunar ejecta-associated particle fluence at 0.1 – 10 mm sizes could produce upwards of years to of order a decade of equivalent background meteoroid impact exposure to satellites in near-Earth space late in 2032,” the team explains, adding, “the instantaneous flux meteoroid flux – if the asteroid impacts the Moon in a favorable spot – could reach 10 to 1,000 times the background sporadic meteor flux at sizes which pose a hazard to astronauts and spacecraft.”
“Our results demonstrate that planetary defense considerations should be more broadly extended to cis-lunar space and not confined solely to near-Earth space.”
According to the team, ejected material could pose hazards to the Lunar Gateway and surface operations on the Moon as ejecta falls back towards it, as well as satellites in Earth orbit.
“There is some risk but it depends a lot on exactly where the asteroid impacts, if at all. We will probably know this soon after the asteroid returns to visibility (it’s too far/faint to see at the moment) in 2028,” Wiegert explained to IFLScience. “But I understand that NASA is already considering how to respond, if necessary.”
Those NASA plans, it transpired, included the possibility of nuking the asteroid to save the Moon, as well as Earth’s satellites. While astronomers are confident that the asteroid will not strike the Earth, we need a further look at it to refine the probability of it slamming into the Moon.
That looked like a bit of a problem for some time, with the object thought to be out of view of our telescopes until mid-2028. That wouldn’t leave much time to launch a mission, were it deemed necessary to attempt to deflect or destroy the object. But according to a recent paper, which attempted to size the asteroid, we may get another, slightly challenging, chance to view the asteroid in 2026 using JWST.
“The destructive power of an impacting asteroid is primarily estimated by knowledge of its size. Asteroid 2024 YR4 reached a peak 2032 impact probability with Earth of 3%, motivating a desire to determine its size,” the team explains in their paper. “Owing to its infrared capabilities, JWST is uniquely suited for such assessment, especially for decameter-scale objects. We used JWST to observe 2024 YR4 and find a diameter of 60 ± 7 m. This size range corresponds to an albedo for 2024 YR4 of 8%–18%, consistent with observation that it is an S-type asteroid.”
That’s a fairly sizeable asteroid, but nothing compared to the impact that killed the dinosaurs, for example. The team adds that an object of this size hits the Earth roughly once every 5,000 years. Though the Earth is not in danger, it is still worth keeping an eye on, to be forewarned of any potential lunar impact.
“At this writing a 2032 impact with the Moon has not been ruled out,” the team adds. “After 2025 May, 2024 YR4 will next enter JWST’s observing window in the first part of 2026 as a challenging target, which may be worth pursuing to determine whether a lunar impact will occur.”
Rivkin and colleagues have since attempted to refine what these observations could show us, and how they will affect the odds of lunar impact. In an update given to New Scientist, they explained that there is an 80 percent chance of the odds of a lunar impact dropping to below 1 percent, and a 5 percent chance of the odds of a lunar impact jumping to over 30 percent. Another chance for viewing the object may present itself in 2027, but that leaves less time to launch a lunar defense mission, were that the option humanity were to go for.
“Observations using the most powerful telescope we have right now are invaluable. Understanding the best ways to use it and how to get the most out of its data is something we can do now with 2024 YR4,” Rivkin told NASA. “This will help us determine the best approach to use during a more urgent observing program should another asteroid pose a potential impact threat in the future.”
“The new observations from this observatory not only provide unique information about 2024 YR4’s size,” he added. “They also added to ground-based observations of 2024 YR4’s position to help improve our knowledge of its orbit and future trajectory.”
[H/T: New Scientist]
Source Link: In 2032, Earth May Be Treated To A Meteor Shower Like No Other, Courtesy Of "City-Killer" Asteroid 2024 YR4