How did the Earth capture the Moon ?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by river, Apr 26, 2020.

  1. davewhite04 Valued Senior Member

    Planet became the asteroid belt I take it? I like the Mars theory.
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  3. paddoboy Valued Senior Member

    Yes, of course. And that has been pretty well validated through samples brought back from the Moon. The planetary, Mars size body was probably a Trojan Asteroid that was dislodged by Jupiter's gravity. Computer simulations suggest that it was traveling at around 4 km/s when it struck Earth at an estimated 45 degree angle.
    Again, I'll get a thread going in the sciences, and post as many reputable links as I can.
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  5. davewhite04 Valued Senior Member

    That fits with Sumerian mythology, maybe Greek too. They used different words to describe astonomical bodies, so science can actually explain it as we go, we need more evidence, science always needs more evidence.
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  7. Halc Registered Senior Member

    Yes. Free thoughts is hardly the place for this kind of discussion.
    In the interest of getting some details down:

    That month will be about twice the current duration of a month, and it thus must involve an orbital radius of around 1.6 the current distance, per Kepler's 3rd law. It will take a lot longer than a couple billion years to do this. More like 50 billion, before which the sun will expand and probably swallow the whole system.

    Of course. Just don't reply. Don't feed the trolls.

    That's the problem. How can anything falling in from outside the Earth system be moving at less than escape velocity of at least 11 km/sec not to mention the 17 km/sec you get from falling in from the area of the asteroid belt. For it to be moving at 4, it needs to already be moving with Earth, which is why I find it sort of plausible that it came from one of Earth's Lagrange points.
    Also, if it was moving at a mere 4km/sec and even slower after the collision, where did it go? It's not moving fast enough to get away. Did it just join with Earth?
    Last edited: May 20, 2020
  8. paddoboy Valued Senior Member

    Nice post, thanks.
    Just on the above, I am going from memory entirely and as an old bugger at times that may be faulty. But in saying that, I'm fairly sure the Sun will enter its giant red phase in about 3 to 5 billions years? It is also now around 5 billion years old and the projected lifetime is I thought about 10 billion years.
  9. Halc Registered Senior Member

    Yes on the timescale. It isn't a question of if Earth will tide lock to the moon before then. Not by a long shot. What seems questionable is if Earth will be swallowed or not. It's not in stone since we're kind of just at the right distance to maybe escape that. If so, the moon continues on outward for a long time, and then after a much longer time (trillions of years??), slowly comes back to where our month and day both resemble the old length of the day back in the Theia days of about 10 hours. Eventually, the moon crosses the Roche limit and breaks up, giving Earth some nice rings for a while, which would be a lot prettier if our sun still lit them up.
    paddoboy likes this.
  10. paddoboy Valued Senior Member

    OK, thanks for that...I blame old age!!!

    Please Register or Log in to view the hidden image!

    I also found this which supports your post.....

    Like I said, probably tomorrow I'l get a thread started in the sciences and away from the trolls.....
  11. James R Just this guy, you know? Staff Member

    When you make declarations like this, you need to back them up with an explanation of the evidence that supports your claim. This is particularly the case when your claim goes against the scientific consensus.

    Nobody should care about what you disagree with, unless you can provide reasons for your disagreement. You gut feelings and wishful thinkings aren't of much interest.

    It does and it did. Again, you need to provide an argument, preferably with evidence, if you're going to set yourself up as an authority.

    Everything of value in science is a theory.

    Again, you give no reason why you believe it is "more likely" the Moon came from outside the solar system. In fact, I think you'd be hard pressed to find any source to support your belief (well, maybe a crank source or a shoddy, unreliable one, but you didn't even bother looking at any of those, did you?).

    And you don't know what inertia is, do you?

    There are probably some. Stupid finds its own level.

    Another pronouncement from you with nothing at all to support it. Not even the tiniest effort on your part.

    And again.

    In light of your behaviour in this thread, river, I have given you a formal warning for trolling.

    I don't believe that you're actually as stupid as you pretend to be here. You're stupid, but surely not this stupid. I have to conclude that you're deliberately trolling by making controversial claims to try to provoke a reaction from well-intentioned science explainers.

    Your baiting of paddoboy in this thread, on its own, deserves a warning.
    Last edited: Jun 18, 2020
    Kristoffer likes this.
  12. James R Just this guy, you know? Staff Member

    Due to accumulated warning points, river will be taking a day off.
    exchemist and Kristoffer like this.
  13. paddoboy Valued Senior Member

    Thanks for some final action. I just need to say that I'm totally aware of river's baiting, but I'm also of the opinion that inane wrong claims need refuting.Let me also say that I'm also aware of another party at present baiting me...and again I believe hidden accusations and inuendo, needs refuting.
  14. paddoboy Valued Senior Member

    A simply put explanation of the Earth/Moon gravitational system shown in the following.......
  15. paddoboy Valued Senior Member

    Here's another more comprehensive video that entails the formation of the Moon due to a collision of the Earth with another planetary sized body, early in the history of the solar system formation......
  16. paddoboy Valued Senior Member

    Probably the most asked question with regards to the Earth/Moon formation theory, is where is Theia now?
    I found the following which answers that question........

    We May Have Finally Found a Chunk of Theia Buried Deep Inside The Moon

    9 MARCH 2020

    Around 4.5 billion years ago, something the size of Mars collided with a newly formed Earth, to colossal effect. This object is not only thought to have fused with Earth and primed it for life, it also broke off a large chunk that went on to become the Moon.

    This story is known as the giant-impact hypothesis; the Mars-sized object is called Theia; and now, for the first time, scientists believe they've found traces of Theia in the Moon.

    The giant-impact hypothesis has been the favoured model for explaining the formation of the Moon for years.

    "This model was capable of accounting for the then-recent observations from samples returned by the Apollo missions, which included the Moon's low iron content relative to Earth, depletion in volatiles and enrichment in refractory elements, while avoiding most of the pitfalls of previous lunar origin theories," researchers from the University of New Mexico wrote in their paper.

    But there was one big spanner stuck in the works.

    Models predicted that around 70 to 90 percent of the Moon should have been made up of mooshed and reformed Theia. However, oxygen isotopes in lunar samples collected by Apollo astronauts were very similar to terrestrial oxygen isotopes - and very different from oxygen isotopes on other Solar System objects.

    One possible explanation is that Earth and Theia had similar compositions to start with. Another is that everything got completely mixed during the impact, which, according to simulations, isn't very likely.
    more at link....

    They acquired a range of samples from different rock types gathered on the Moon - both high- and low-titanium basalts from the lunar maria; anorthosites from the highlands, and norites from the depths, brought upwards during a process called lunar mantle overturn; and volcanic glass.

    For the new analysis, the research team modified a standard isotope analysis technique to produce high-precision oxygen isotope measurements. And they found something new indeed: that oxygen isotopic composition varied depending on the type of rock tested.

    "We show," they wrote in their paper, "that the method of averaging together lunar isotope data while ignoring lithological differences does not give an accurate picture of the differences between the Earth and Moon."

    In fact, the deeper the rock sample's origins, the researchers found, the heavier the oxygen isotopes, compared to Earth's.

    This difference could be explained if only the outer surface of the Moon was pulverised and mixed during the impact, resulting in the similarity with Earth. But deep inside the Moon, the Theia chunk remained relatively intact, and its oxygen isotopes were left closer to their original state.
  17. paddoboy Valued Senior Member

    the paper:

    Distinct oxygen isotope compositions of the Earth and Moon:

    The virtually identical oxygen isotope compositions of the Earth and Moon revealed by Apollo return samples have been a challenging constraint for lunar formation models. For a giant impact scenario to explain this observation, either the precursors to the Earth and Moon had identical oxygen isotope values or extensive homogenization of the two bodies occurred following the impact event. Here we present high-precision oxygen isotope analyses of a range of lunar lithologies and show that the Earth and Moon in fact have distinctly different oxygen isotope compositions. Oxygen isotope values of lunar samples correlate with lithology, and we propose that the differences can be explained by mixing between isotopically light vapour, generated by the impact, and the outermost portion of the early lunar magma ocean. Our data suggest that samples derived from the deep lunar mantle, which are isotopically heavy compared to Earth, have isotopic compositions that are most representative of the proto-lunar impactor ‘Theia’. Our findings imply that the distinct oxygen isotope compositions of Theia and Earth were not completely homogenized by the Moon-forming impact, thus providing quantitative evidence that Theia could have formed farther from the Sun than did Earth.

  18. elte Valued Senior Member

    Some thoughts about the moon based on the theory that a Mars-sized object smashed into the earth when it was relatively young. Such an impact knocked huge amounts of rubble into space. Of that, a huge quantity went into orbit around Earth. It eventually conglomerated into the moon.

    An interesting thing is how the near side of the moon has been more geologically active than the far side.

    I figure the reason is that gravity pulls harder on heavier elements than lighter ones. The heavier elements have a greater tendency to be radioactive than lighter ones. I'm thinking of uranium and thorium, etc. They would tend to coalesce on the near side of the moon and their presence there, along with, I'm guessing, other heavier elements, helps to explain why the moon's rotation is gravitationally locked to the earth, the moon having just one rotation per revolution around Earth.

    The radioactive elements tending to be on the near side would heat up the subsurface more there. It's why I think the near side has had much more volcanic activity than the far side.
  19. billvon Valued Senior Member

    Why do you think there would be more force acting on elements on the near side of the moon?
  20. elte Valued Senior Member

    I was thinking the distance to earth is a bit less on the near side than the far side, somewhere on the order of a percent if the moon has a couple thousand miles diameter and a distance of a couple hundred thousand miles from Earth. A very small difference, but in the microgravity and vacuum conditions out there where the moon is, I was thinking that could settle in the heavier particles closer to the earth as the moon condensed.
  21. billvon Valued Senior Member

    Right, and centrifugal force is about a percent higher. That's why we have tides.
  22. exchemist Valued Senior Member

  23. Janus58 Valued Senior Member

    The Moon wouldn't have condensed in its present tidally locked state. The fact that it was formed from debris orbiting the Earth would have given it a good deal of spin at first. It wasn't until later that it settled into tidal lock.
    Now, if the Moon as it condensed, did end up a bit asymmetrical, where it's center of mass and geometrical center where not the same spot, then it would tend to settle into a tidal lock with these two aligned so they pointed towards the Earth. This is the present situation for the Moon; its CoG is displaced ~2km towards the Earth from its geometrical center.
    Overall, the Moon is not gravitationally symmetrical. It has a good number of mass concentrations or "mascons", which are, for the most part, associated with impact basins. ( These mascons actually make it hard for long term stable lunar orbits to exist)

    So it it more likely that early events in the Moon's history gave it an asymmetry, and that asymmetry influenced how the Moon aligned when it achieved tidal lock.
    exchemist likes this.

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