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The mother of all meteor showers could threaten satellites

Shortly after astronomers detected asteroid 2024 YR4 on December 27, 2024, they realized it posed no threat to Earth. But it could still impact the moon in 2032. The impact debris could threaten satellites and trigger an extraordinarily stunning meteor shower.

Asteroid 2024 YR4 is about 53 to 67 meters (174 to 220 ft) in diameter. It's the same size as the asteroid responsible for the Tunguska Event in 1908. It has a ~4% chance of striking the moon in 2032, and if it does, it will excavate a crater about 1 km in diameter, though estimates range from 0.7 to 1.4 km depending on the lunar surface material. The blast would be equivalent to about 65 megatons of TNT and, according to new research, would send about one hundred thousand tons (10⁸ kg) of debris into space. This cloud of debris could pose a hazard for satellites.

The research is titled "The Potential Danger to Satellites due to Ejecta from a 2032 Lunar Impact by Asteroid 2024 YR4." The lead author is Paul Wiegert from the Department of Â鶹ÒùÔºics and Astronomy and the Institute for Earth and Space Exploration (IESX) at the University of Western Ontario. The paper is on the arXiv preprint server.

One hundred million tons is a lot, but not all of it will make its way to Earth.

"Depending on the actual impact location on the moon, as much as 10% of this material may accrete to Earth on timescales of a few days," the authors write.

They determined that in late 2032, if 2024 YR4 strikes the moon, the satellites near Earth would be exposed to a decade's worth of equivalent background meteoroid impact exposure.

"Of primary concern are ejecta particles above the impact hazard threshold (0.1 mm) for satellites delivered directly to low Earth orbit (LEO) on relatively short (days to a few months) timescales and that could pose a hazard to spacecraft," they write.

The researchers' goal was to determine what the short-term effect of 2024 YR4's impact on the moon would be.

"We emphasize that there exist order of magnitude uncertainties in the following analysis," they explain as a caveat. They estimated five important factors:

• The size of the crater.
• The amount of material ejected into space.
• The size frequency distribution of the escaped ejecta.
• The range of locations for the impact on the moon.
• The delivery efficiency of escaped ejecta reaching near-Earth space.

The impact debris that reaches escape velocity will not disperse isotropically. The fraction that reaches Earth depends heavily on the impact location.

"Because the moon is orbiting Earth at approximately 1 km/s, for ejected material to reach Earth quickly, the impacting object needs to hit the trailing edge of the moon in such a way that the ejected material's velocity, after rising out of the moon's gravitational well, largely cancels out the moon's orbital velocity," the authors write.

It starts with the lunar impact corridor, which is based on the Center for Near-Earth Object Studies (CNEOS) Small-Body Database. From the variables in 2024 YR4's computed trajectory, the authors simulated 10,000 clones of the asteroid and their trajectories. In total, 410 of them struck the moon. The impact would likely be on the southern hemisphere of the moon's leading side.

The researchers investigated four of the 410 simulated impacts to determine how much ejecta could reach Earth. They found a significant probability that 2024 YR4 will strike a location on the moon that delivers 10% of the impact ejecta quickly to near-Earth space.

Earth and its satellites are subjected to a continuous stream of debris that's part of the background environment. It's well understood and expressed as a mean annual flux: ∼ 1 meteoroid D > 100 µm, ∼ 10^−3 meteoroids D > 1 mm, and ∼ 10^−7 meteoroids D > 1 cm. The authors say that the impact ejecta from 2024 YR4 would greatly exceed that in only a few days.

"The instantaneous flux could reach 10 to 1,000 times the background sporadic meteor flux at sizes that pose a hazard to astronauts and spacecraft," they write.

This increased environmental exposure of our satellites to debris would accelerate their aging and shorten overall lifespans. This is particularly true for satellites in LEO, which constitute the majority of satellites. Almost 90% of satellites are in LEO.

"This will all occur during the few days of maximum ejecta delivery from a 2024 YR4 impact," the researchers explain.

By 2032, that number will grow and so will the LEO satellite cross-section, increasing the risk and potential damage.

"Given the very large total exposed area for satellites by 2032, it becomes possible that hundreds to thousands of impacts from mm-sized debris ejected by a lunar impact from 2024 YR4 will be experienced across the entire satellite fleet," the authors write. They also point out that due to particle size, impacts can damage satellites but are unlikely to be mission-ending.

However, by 2032, the risk could encompass more than satellites. Our presence on the lunar surface could mean more dangerous exposure.

"The ejection of material from the moon could be a serious hazard to moon-orbiting spacecraft (e.g., Lunar Gateway), but would likely pose even greater dangers to any lunar surface operations, given that most ejecta mass will accumulate across a wide swath of the moon," explain Wiegert and his co-researchers.

As it stands, the odds of 2024 YR4 impacting the moon in 2032 are low, only about 4%. In 2028, the asteroid will pass harmlessly by Earth, giving astronomers another opportunity to observe it and constrain its future trajectory. That will lead to more accurate determinations of the potential impact site, which will lead to an updated understanding of the risk the debris poses.