We might already be too late to knock ‘city killer’ asteroid 2024 YR4 out of the way with a tested method, a scientist has warned.
The space rock has a 2.3% chance of hitting Earth in in 2032, according to current estimates,
Nasa is trying to get a better idea of its intended route by looking at it with the James Webb space telescope, but with only eight years before its possible hit, we could already be short on time.
Dr Robin George Andrews, author of How to Kill an Asteroid, gave an unsettling warning that to properly mount a planetary defence mission, you need at least a decade to plan and execute it.
An emergency situation might come down to either evacuating the potential impact site, or blasting the asteroid with a nuclear bomb in space, he said.
The science journalist and author told Metro that the only method we’ve currently ever used to deflect an asteroid nudged it only slightly at first. If we did the same with YR4, it could take a long time to amount to a significant change in trajectory.
‘It’s not like you’re playing pool, and you hit the cue ball into something and it flies off in the other direction,’ he said. ‘Eight years is tight, basically.’
If hitting it wouldn’t be enough to safely knock it off course, there is the nuclear option… literally.
‘This has never been tested in space because it’s technically illegal, and it would cause tensions,’ Dr Andrews said.
‘But if you put a nuclear weapon next to an asteroid – chased it through space, basically – and detonated it, it would give it an even bigger push.
‘If the choice was to evacuate the area or maybe use a nuke to deflect it… I imagine people are talking about that as a possibility.’
This woud break a current taboo against the use of nuclear weapons, but the explosion itself would not have negative consequences for us as ‘it would be so far away that we wouldn’t even see it.’
Such a drastic method ‘would never be a first resort,’ though.
Nasa’s DART mission in 2022 was the first and only time humans ever deflected an asteroid, when 160m-wide Dimorphos was hit causing its orbit time to shrink by 33 minutes.
Dr Andrews said that this method, where the asteroid was slammed into by a spacecraft the size of a van, had risks: ‘You don’t want to deflect it so it hits somewhere else on Earth, or breaks up into fragments that are still big and may hit random spots.’
The asteroid known as YR4 is smaller than Dimorphos, so there is a good chance we could alter its trajectory at least by some degre.
And don’t forget there’s a good 97.7% chance the asteroid will miss the Earth altogether, and no deflection will be needed.
If it really starts to look like a direct hit, though, governments and space organisations will speed up efforts to deflect it. One option could be developing a more powerful deflection spacecraft than the one used in the DART mission.
What would happen if 2024 YR4 hit Earth?
It depends where it hit, how big it is, and what it is made of.
If it came down in the sea, then there would be the possibility of tsunamis, but ultimately it wouldn’t be much of a problem. Given that the planet is mainly covered by water, this is the most likely thing to happen.
Things would get hairy if it came down on land, particularly if it came on course to hit a city, and if it was as large as 90m.
Dr Andrews explained that in that unlikely scenario: ‘It would be a terrible day.
‘It may or may not leave a crater in the middle of the city, because it might not hit the ground.
‘It might blow up in the air, but the explosion is the main problem, because it would make a massive blast wave which would kill a bunch of people in the middle, and multistorey buildings for a few miles around would be knocked down. For tens of miles around, people would be at risk of serious injury.’
If it turned out to be on the smaller side of our calculations, at 40m, a hit would still be ‘not great’ but would be considerably better.
‘It would be like the Chelyabinsk one [an asteroid strike on Russia in 2013] on steroids. Some buildings may collapse, windows will implode like shotgun shells. People will injured and probably killed near the middle, but it will be ten times less bad than the 90m one.’
Ultimately, if it hit any city, that city would know about it – so it’s good we have enough notice to either do something about it, or simply run away if it’s coming close.
‘If you can hit it more aggressively with a bigger spacecraft, you could give it a bigger push in the other direction,’ Dr Andrews said.
‘I cannot see a situation where SpaceX would sit it out, and they’re good at making things quickly.’
The scientist wrote a thread on X outlining what he sees as the potential difficulties in any planetary defence misson, which made headlines for its warning that we can’t just bash into any asteroid heading our way and be sure of success, particularly if time is short.
If an asteroid is hit too hard, it might shatter causing problems in itself: ‘As I often say, it’s like turning a cannonball into a shotgun spray.’
The James Webb telescope, which is the most powerful ever made, should be able to tell us more about YR4’s size, and possibly its composition too.
It will have another couple of months to make its observations and work out how much we need to worry, before the asteroid heads too far from our neighbourhood to be seen. After that, if we still don’t know, we’ll have to wait until it’s next back in 2028.
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