What happens if the asteroid collides with the Moon?
The chances of a collision with the Moon have increased significantly. But what does that mean for us?
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At first, asteroid 2024 YR4 seemed like a potential threat to Earth, but that risk has since been greatly reduced.
The asteroid is estimated to be between 30 and 65 metres wide.
Meanwhile, the chances of it hitting the Moon have increased. It was recently revealed that it had more than doubled, from 1.7 to 3.8 per cent, according to NASA.
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There is still a much greater chance that it will whiz past the Moon.
But what does this mean for the Moon and Earth? Several readers have asked us whether a potential impact on the Moon would have any significant consequences for us on Earth, and whether such an impact could affect the Moon's orbit.
Much, much larger asteroids
This asteroid is about the size of a large building, and it's hurtling along at tens of thousands of kilometres per hour.
If the small chance materialises and it actually hits the Moon, it would happen on December 22, 2032, according to current estimates.
But even though the asteroid has enough force to create a formidable crater on the surface, it is far too small to have any effect on the Moon's orbit, Stephanie Werner writes in an email to sciencenorway.no.
She is a professor at the University of Oslo's Centre for planetary habitability.
"I don't think any of the known asteroids would alter the Moon's orbit, because the masses of the asteroids compared to the Moon are too small," she writes.
We're talking about asteroids that can be many kilometres wide – much, much larger than 2024 YR4.
The Moon is massive. It is among the largest moons in the entire solar system. In fact, it is even bigger than Pluto, the dwarf planet located on the outer edge of the solar system.
Werner points out that the Earth-Moon system is very stable. Although some models show that the Moon's rotation may have been altered in the past by very large asteroid impacts, says Werner. But this asteroid is not nearly that large.
A powerful flash of light?
The impact will have no effect on Earth, astronomer Jan-Erik Ovaldsen writes in an email to sciencenorway.no. He runs the astronomy website himmelkalenderen.com.
However, there is a chance that we might be able to see the impact itself – if it happens on the side of the Moon that faces us. We never see the far side of the Moon from Earth.
"I can't estimate the visibility myself, but some astronomers believe it wouldn't be visible to the naked eye due to bright light. Others think there's a good chance we would see a flash of light, even in broad daylight," he writes.
This depends on where exactly the impact occurs. It could happen on the shadowed part of the surface, or in the sunlit area. When there's a full moon, the entire surface facing us is illuminated by the Sun.
"On the estimated date of impact, about 70 per cent of the lunar disc will be illuminated. Preliminary calculations show there's a much higher chance the impact would occur on the illuminated side," according to Jan-Erik Ovaldsen.
He points out that impacts have previously been observed on the shadowed side of the Moon as visible flashes of light. One example of a flash can be seen in an amateur video from 2023, in the bottom right corner.
私の観測史上最大の月面衝突閃光を捉えることができました！2023年2月23日20時14分30.8秒に出現した月面衝突閃光を、平塚の自宅から撮影した様子です（実際の速度で再生）。なんと1秒以上も光り続ける巨大閃光でした。月は大気がないため流星や火球は見られず、クレーターができる瞬間に光ります。 pic.twitter.com/Bi2JhQa9Q0
— 藤井大地 (@dfuji1) February 24, 2023
"If the chances of a Moon collision remain or increase, we can expect professional observatories, space probes, and thousands of amateur astronomers will be watching closely," he writes.
Stephanie Werner believes the asteroid would create an impact large enough to be seen with a good amateur telescope – if the collision happens, and if it's on the side facing Earth.
Unfortunately, she thinks there is a greater chance the collision would occur on the far side, hidden from view on Earth.
So now it's just a matter of waiting: Will the odds increase as we approach 2032? Or will 2024 YR4 quietly disappear back into the solar system?
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Translated by Alette Bjordal Gjellesvik
Read the Norwegian version of this article on forskning.no
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