Earth's wobbly companion is probably the result of a lunar impact, reckon space boffins A freshly discovered train-sized rock that tags along with Earth as a constant companion orbiting the Sun is most likely a fragment of the Moon resulting from an ancient lunar impact. 469219 Kamo'oalewa – discovered by observers in Hawaii in 2016 – is about 41 metres in diameter and orbits the Sun in a trajectory not …
The moon is covered in massive craters from strikes going back about 4 billion years, the earth has probably had a similar number of strikes but the majority of them have been hidden by the way our world has evolved over the same period of time - the dinosaurs were removed by a large strike about 66 million years ago but we have to dig down into the earths crust to verify that it happened. Until quite recently we all thought:
You know tyrannosaurus rex was destroyed before, by a furry little ball that crawled along the primeval jungle floor. He stole the eggs of the dinosaur." - Jefferson Airplane Mau Mau (Amerikon)
The animation says "Half the time, it's orbit takes it closer to the sun and it passes ahead of the earth. The other half of the time it is farther from the sun and calls behind"
Um.. Isnt that true of everything that orbits the Earth???
(Anon. because I'm probably being stupid and you'll all laugh at me, as I will deserve!)
I think the simplest answer is that a true satellite lies within what they call the Hill sphere. The Hill sphere to an object is the region where its gravity dominates. Remember it is quite far out, around 0.1 AU. Both of us “just happen” to orbit the sun in the two different orbits with the same orbital period and about the same place in the orbit. Remove the sun and I think we would just drift apart.
Hill sphere of a body is defined by other massive bodies near it. For the Earth that means, mostly, the Sun. If you removed the Sun Hill sphere of Earth would change radically (it would get much larger). Body might then be within this new sphere and might have less than escape velocity, so might very well then be orbiting Earth-Moon system. Too lazy to do the celestial mechanics to work that out.
There are two tiny moons of, I think, Saturn, that do the same thing. They swap positions from time to time without ever colliding.
What caught my eye about this rock was how it had reddish coloration and this led them to think it was Lunar in origin. But Omuamua, the recent interstellar vistor, ALSO had red coloration, and so does Arrokoth, the peanut-shaped Kuiper Belt object recently visited by the New Horizons spacecraft. It looks like reddish hues are common for rocky objects subject to very long term cosmic radiation.
So being in such a close orbit to Earth is probably a better argument for being a result of the Earth/Theia collecition that created our Moon, than any particular surface chemistry.
This thing is a quasi-satellite of Earth: it is where it is only because of Earth. Further it is not clear how stable the system is. It has been there only perhaps for a century or so and will probably remain for some centuries more. But probably not for very long at all. Has been previous body doing similar thing: it's gone now and only was there for decade or so I think.
Maybe not ... it was originally called Yellowjacket for a reason, and it's a long way from the nearest cold beer. Note that the telescope is not open to the general public. If you are interested in that kinda thing you'll want to visit their main campus at Mars Hill, Flagstaff Arizona. Well worth the trip, recommended.
Planet sized objects tend to act as liquids, more than solids, The strength of the crustal materials are as nothing to the forces available in a collision. What comes out of the collision is either liquid, gas or comminuted debris. Given time, since they all tend have a common velocity, they could coalescs under the common gravity field, but it would not be a fragment in the sense of being a broken off bit of either the impactor, or the impacted
This is a slight confusion. Planets are indeed essentially liquids: this is why they are spherical (apart from very spinny ones). but this is on large scale: on small scale material near surface (and further down than that for The Moon) does not act like liquid (neither does for instance, clump of 100 water molecules probably).
What comes out of collision is lots of chunks of stuff including dust, gas, probably actual molten rock and so on. On large scales these will coalesce into other body and behave as liquid (if giant impact hypothesis is correct The Moon is one such body, coalesced from bits of pre-Earth and whatever hit it).
On small scales – scale of bus or building say – these chunks do not behave like liquid, and chunks this size may be ejected, and may avoid coalescing. This is such a chunk.
Other good example are Martian meteorites.
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