2024 YR4 Asteroid 3.1% chance of colliding with Earth

Cities cover roughly two percent of the world's land surface, so even if the asteroid did hit Earth, when you consider that 25% of planet surface is land, then the chance of directly striking a city is only half a percent (until more precise trajectory is calculable). The greater danger could be massive forest or range fires, if there was an airburst over land. Or would there also be a tidal wave possible with a sea strike? - don't know if it would be massive enough.
 
It isn't really unusual for the odds for collision to go up with time, at least at first. Look at it this way: Your first prediction gives a cross-section of where the asteroid could be when is crosses Earth's orbit. Earth is in that cross-section, offset from the center. The odds of collision are determined by how large the Earth's cross-section's area compares to that of the cross-section of the asteroid's path. You get an more refined prediction, resulting in a smaller cross-section for the predicted position of the asteroid. The Earth takes up a larger percentage of this, so the predicted odds of collision go up. But, as the predictions get better, and the asteroid's cross-section continues to shrink, you eventually reach a point where the part of the Earth's cross-section starts to be outside of it, and the odds start to go down until the whole Earth is outside of the predicted path. Of course this is assuming that the center point of the predicted path isn't also shifting towards the Earth.
 
TheVat said:
Cities cover roughly two percent of the world's land surface, so even if the asteroid did hit Earth, when you consider that 25% of planet surface is land, then the chance of directly striking a city is only half a percent (until more precise trajectory is calculable). The greater danger could be massive forest or range fires, if there was an airburst over land. Or would there also be a tidal wave possible with a sea strike? - don't know if it would be massive enough.
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The Wikipedia page on 2024 YR4 has this for the risk corridor -

700px-2024_YR4_risk_corridor.png



Going by Chelyabinsk (around 10 tons) the damage risks from one that is probably at least 10,000 times larger has to be very high. Lots of blown out windows (and injuries from that) around Chelyabinsk as well as eye and ear injuries, UV skin burn, headaches. Not nearly hot enough to start fires but a big one probably can, both from downwelling radiant heat and from ground impacts and hot debris.

I found this article - https://www.sciencedirect.com/science/article/abs/pii/S0019103518305104 - which had this about Chelyabinsk -

A population of 1.7 million people lived in the affected area (Popova et al., 2013). About 1% of the 1758 people who chose to submit an online report in the weeks after the event reported some form of injury, mostly sunburn, hurting eyes, temporary deafness and headaches (Popova et al., 2013; Kartashova et al., 2018). A fraction of 4.4% of respondents who were outside ended up with some level of sunburn, suggesting an energy dose of far-UV radiation >0.7 kJ/m2 (Huang et al., 2010). More than half reported they could feel the heat from the fireball. No fires were ignited by the event. Ignition of ground litter requires about 350 kJ/m2 (Glasstone and Dolan, 1977) and this limit was not reached. Eardrums will typically rupture at about 16 kPa (Mannan, 2005), but no reports of such injuries were made. Instances of both glass cuts and being hit by (or blown into) obstacles were usually found at similar frequencies in the area where overpressures were >1 kPa, independent of the distance from the Chelyabinsk meteoroid trajectory out to about 50 km (Kartashova et al., 2018).
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I don't know if an object of 2024 YR4 size would break up as an air burst even if loose rubble. Some of the rubble could be quite large - and may be protected from breaking up by material ahead of it. I also don't know that an air burst would greatly reduce the damage - may just mean different kinds of damage.
Pinball1970 said:
2032 is when it could hit so NASA will be assessing Probability, trajectory and if DART will have to step in!
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No "have to" in this case, unfortunately. If it were a case of could hit anywhere, maybe but knowing it won't hit the USA and might hit places like Sudan or Yemen?

Whilst meteor detection is (according to Pew Research) the most widely supported NASA objective amongst Americans I am not so sure they would support a big and expensive effort to divert one that is not expected to hit or affect the USA. Not that I think it should be decided purely on the basis of popularity. As a demonstration of US benevolence and international cooperation maybe. Or demonstrating technological (military) superiority, maybe.
 
Ken Fabian said:
I don't know if an object of 2024 YR4 size would break up as an air burst even if loose rubble. Some of the rubble could be quite large - and may be protected from breaking up by material ahead of it. I also don't know that an air burst would greatly reduce the damage - may just mean different kinds of damage.
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An interesting possibility is a VERY near miss - a few miles. If it's close enough it will experience aerobraking which could result in fragmentation (very bad for our satellite constellations) or even capture. Any capture would allow us to go out and look at it with today's technology (i.e. a Falcon Heavy size launch.)
 
billvon said:
An interesting possibility is a VERY near miss - a few miles. If it's close enough it will experience aerobraking which could result in fragmentation (very bad for our satellite constellations) or even capture. Any capture would allow us to go out and look at it with today's technology (i.e. a Falcon Heavy size launch.)
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It would be an extraordinary circumstance (very low relative velocity?) where an asteroid ends up in an orbit around Earth. I don't think this one is a candidate.
 
foghorn said:
It seems at the moment estimated impact velocity is something like 13 to 17 km/s
That's if I'm understanding the details in Link...
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Odds continuing to reduce.

phys.org

Chance asteroid 2024 YR4 will hit Earth down to 0.001 percent, ESA says

The chance that a football field-sized asteroid capable of destroying a city will strike Earth in 2032 has fallen to 0.001 percent, the European Space Agency said on Tuesday.
phys.org phys.org
 
In case you missed it here it is.

1743770280555.png


Not the most spectacular Webb image, however this Asteroid is significant in terms of size, it is estimated to be about 60M.

Keep in mind that the Chelyabinsk meteor that exploded over Russia crated a shockwave that damaged 1000s of buildings and injured 1500 people.

That was the equivalent of 20-30 Hiroshima bombs.

That was less than a third of the size of YR4.


If it does hit the moon it will do so with far greater velocity than the Chelyabinsk meteor I would have thought, no atmosphere on the moon to slow it down.
The momentum will also be greater due to mass.
 
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