In 2032, Earth May Witness A Once-In-5,000-Year Event On The Moon

An asteroid discovered last year and briefly thought to be a threat to Earth has a one-in-23 chance of hitting the Moon, according to NASA estimates based on JWST data. A new paper outlines how this could be a spectacular one-in-5,000-year event, potentially ejecting material towards Earth.

Asteroid 2024 YR4 was first discovered on December 27, 2024. Astronomers have been keeping a close eye on it ever since, as initial observations showed around a 1 percent chance that it could collide with Earth on December 22, 2032. Follow-up observations of the asteroid briefly showed a higher chance of the asteroid making an impact. At 3.1 percent, it briefly became considered the most dangerous space object since tracking began.

Thankfully, as repeatedly predicted by astronomers during that slightly nervous time, as more observations came in, the chances of impact with Earth fell dramatically, and now stand at around 0.004 percent.

But the Moon may not be so lucky.

“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. 

“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!”

Back then the object had a 3.8 percent chance of hitting our natural satellite, but following further 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 have updated the chance of impact with the Moon on December 22, 2032, to 4.3 percent. On that date, it will pass around 0.00007 Astronomical Units (AU) of the Moon, with 1 AU being the distance between the Earth and the Sun.

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. In short, it would be pretty spectacular, potentially even causing a 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 new 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 explains 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 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, 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."

In short, it would be a spectacular and rare event, that you may even get to gawp at in the form of a meteor shower. The impact itself may be harder to spot, though not impossible.

"If the impact happens on the side of the Moon towards the Earth, the impact will be visible though hard to catch," Wiegert added. "There will be a brief bright flash followed by a dust cloud that will disperse over a few minutes. But the cloud and the resulting crater (which will be about a km across) will be near the limit of what can be clearly seen from Earth. Spacecraft in orbit will get a much better view."

With the odds of impact still low, we might not get this space treat. Right now, the asteroid is too far from human telescopes to get a good look at it, but we will get another look at it before it makes its close approach in 2032.

"Asteroid 2024 YR4 is now too far away to be observed with space-based or ground-based telescopes," NASA explained in a statement. "NASA expects to make further observations when the asteroid's orbit around the Sun brings it back into the vicinity of Earth in 2028."

The paper is submitted to the American Astronomical Society and is available on pre-print server arXiv.