Probability of Asteroid 2024 YR4 hitting the Moon increases The chance of Asteroid 2024 YR4 hitting the Moon has increased, according to boffins making observations from the James Webb Space Telescope. NASA said data from the telescope "improved our knowledge of where the asteroid will be on Dec. 22, 2032, by nearly 20 percent." The upshot is that there is now a 4.3 percent possibility …
"And the chance of it hitting the moon hasn't changed, just the estimate of the probability of it doing so."
That's a bit deep. The likelihood of this asteroid hitting the Moon in 2032 is fixed now until then but our knowledge of that exact probability is imperfect?
I am not sure that is the case as the most minuscule chaotic perturbations even those that are ultimately quantum in origin would render arguable the idea that the asteroid has an exact position and velocity that it will occupy seven years hence.
Somewhere I encountered the proposition that the Moon's size and orbit had protected the Earth from the constant bombardment experienced during the earlier solar system and had other effects beneficial to the development of life, ocean tides not being the least. Our old scarred satellite seems to have taken quite a number of bullets for us.
Hmmm... 2024 YR4 is about 60m across. The moon, at 1737km radius, is about 60000 times larger in diameter, so it'd have a volume about 2.2e+14 times greater.
The object is probably silicate, with a density comparable to that of the moon. So the moon's mass is probably (again) about 2.2e+14 times that of 2024 YR4.
Impact speed would be about 13.9 km/s. So the change in the moon's speed would be 13.9 / 2.2e+14 km/s = 6.3e-11 m/s. The component of the speed change that is perpendicular to the moon's velocity won't change anything much, but if the rock hits "head on", it will slow the moon by that amount, and if it hits the moon from behind, the moon will speed up by that amount. Either way, the change in speed will be permanent, and there will be a change in the orbital period (admittedly of the order of microseconds).
(Note that I'm simplifying things the orbital mechanics here. But the change in speed will be roughly as indicated above.)
Now we come to the difficult part of the problem (at least for me; I'm an astronomer, not an entomologist.) I don't even know if gnats have external genitalia.
The first hit when searching for "gnat penis size" was
https://en.wikipedia.org/wiki/Muggeseggele
"...a humorous Alemannic German idiom used... to designate a nonspecific very small length... it refers to a housefly's scrotum."
The problem is that the Interwebs have a great deal of information about human penis sizes, and not much about insects. I don't think they'll help. Let's try this another way.
Another search came up with various gnat sizes from 1/16 to 1/8 "inch". Not sure if that's US or International inches, but call it 2mm. Let's be generous to the gnat and assume it's well-endowed, with genitals 1/10 as long as that, or 0.2mm, or 2e-4 metres. I can weasel out here by pointing out that you didn't specify a particular type of gnat anyway; perhaps some of the larger ones would fit my guesstimate. (Or perhaps there's an entomologist lurking in these fora who can comment.)
So, after 2e-4 / 6.3e-11 = 3.2 million seconds, or about five weeks, the moon's orbit would have been diverged from what it otherwise would have been by roughly the suggested amount.
However, that's short-term thinking. After, say, a million years, the divergence will be about two kilometers.
A very comprehensive reply... only spoiled by one thing.... you failed to use El Reg units!
Where are the linguine, grapefruit and adult badgers in your units? any fule kno that El Reg units are topp!
Have a beer anyway ---->
reading that now. Fits perfectly to this topic. But in reality it won't work this well.
The bits of the moon do, but they continue to collide with each other and fall apart and spread. Most of it stays in the orbit. But 1% (was it 1% in the book? Possibly less...) is coming down. Which is enough to cause those problems. But there is also some trigger mentioned 'round 1/3rd of the book which causes a sudden increase of mass reaching the earth, which else might have just passed between earth an moon an no one would have noticed.
But, well, I am just beyond 1/3rd, got enough reading to do, but my vacation last week was hunted by being sick, so not much mood for reading.
All in all the book is, from by scientific guts point of view, quite close to reality with a lot of things.
A fair question. There's no safety aspect here. It should be of some scientific interest, in that it'll give us a look a few metres below the moon's surface at freshly-exposed lunar material, and we may learn a bit about crater formation. We've gotten some knowledge of such things from looking at the craters of the upper stages of Apollos 14 to 17 (they were deliberately aimed at the moon), but this is much larger and heavier.
I would expect at least a few smallish rocks to be ejected into geocentric and heliocentric orbits, mostly the former. (Not lunar orbit.) Such rocks would eventually hit the moon again, or the earth, or be ejected into heliocentric orbits. If they hit the earth, and survive re-entry, and have the good grace to hit land rather than ocean, we get lunar samples without having to send astronauts (Apollo) or a sample retrieval probe (Chang'-es 5 and 6) to do the job.
In 2028, this object will be visible again, and we'll be able to compute a very precise orbit and will know with basically metaphysical certitude if it'll hit the moon. If it does, I'd hope somebody lands a seismometer on the moon between now and 2032 Dec 22. The Apollo missions left such (and measured moonquakes caused by the aforementioned upper stages). It'd be a rare opportunity to really learn something about the moon's internal structure.
(But I'm not getting my hopes up all that much yet. As noted, odds are still against a lunar impact.)
It's true the moon gets hit by things regularly, but they are very rarely a) this big, and b) this well documented. Being this well documented would allow us to actually have front row seats for the impact.
Set up specific cameras, watch from the right spot where the impact occurs, be prepared to carry out proper scientific measurements on the comet beforehand and the Ejecta and the crater itself afterwards.
If this turns out to be going to hit the moon, it gives us the chance to learn a LOT.
Most of the time, we are currently working with craters we didnt see form, or had zero warning of. On those rare occasions where an impact is caught on camera, it's rarely optimally positioned in shot, and just by luck rather than judgement in frame. This would be an amazing opportunity, so personally I'm crossing my fingers, that when it reappears in 2028 that that 4% climbs rather higher...
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