‘City killer’ asteroid on collision course with Moon could damage satellites

New observations of the “city killer” asteroid once thought to be on a collision course with the Earth indicate it will miss the planet but strike the Moon and pose “potential danger” to satellites.

Recent estimates of the building-sized space rock’s trajectory suggest it has a 4 per cent chance of hitting the lunar surface in December 2032.

Astronomers, including from the University of Western Ontario, estimate in a new study that such an impact may release energy equivalent to 6.5 megatons of TNT and produce a lunar crater nearly 1km in diameter.

In comparison, the atomic bombing of Hiroshima by the US in 1945 produced explosive energy equivalent to nearly 0.015 megatons of TNT.

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A strike from the space rock, called 2024 YR4, could generate a lunar debris cloud weighing over 100,000,000kg, according to the yet-to-be peer-reviewed study.

As much as 10 per cent of this debris could “accrete to the Earth on timescales of a few days”. And, depending on the impact location of the asteroid on the Moon, the lunar ejecta could expose satellites to meteorites for years.

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

The risk posed to satellites would depend on several factors, including the location of the impact, size of the lunar crater, the amount of material ejected by the collision, and the size distribution of the escaped ejecta. Of these factors, the study notes, location of the impact was the most critical.

“Because the moon is orbiting the Earth at approximately 1km per second, for ejected material to reach Earth quickly, the impacting object needs to hit the trailing edge of the moon,” it says.

The impact should also happen in a way that the ejected material's velocity “largely cancels out the moon's orbital velocity”.

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The study simulates 10,000 clones of the asteroid taking different trajectories and in 410 of them, the space rock strikes the Moon.

If the asteroid does strike the Moon, it is likely to do so in the southern hemisphere.

Analysing the 410 potential impact scenarios reveals that there is a significant probability of a 2024 YR4 strike delivering 10 per cent of the impact debris to near-Earth space, posing risks to astronauts and spacecraft.

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

Since the number of satellites orbiting the Earth is increasing exponentially, the debris may pose an even greater threat by 2032.

“Given the very large total exposed area for satellites by 2032,” the new study warns, “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.”

Based on the new findings, researchers call for measures being taken to safeguard the Earth from dangerous asteroids to be extended to protect the Moon.