How did the Earth capture the Moon ?
- Thread starter river
- Start date
Janus58
Valued Senior Member
Again, the present model for the formation of the Moon is that it's material was thrown off by the Earth in a collision between another body and the Earth.
The Asimov article you are referencing appears to be "Just Mooning Around", which was collected with other articles in "Of Time Space and Other Things."
All the articles in this collection were written between 1963-65, several years before we able to examine actual Lunar material. A great deal of information on the Moon has been collected since then and led to a good amount of additional thought on the origin of the Moon which has led to the collision hypothesis.
As to the Moon's rotation on its axis. While the Moon does complete one rotation in the same time as it completes one orbit, it does not rotate at the same speed as it orbits at all time. The rate of rotation is steady, but do the eccentric nature of it orbit, the orbital speed changes throughout the orbit. This results with the Moon sometimes rotating at a rate slightly slower than it orbits and sometimes rotating faster. So it rotation alternates between falling behind and speeding ahead. This libration isn't enough to let us see all of the Moon's surface from the Earth, but we do see more than 1/2 of it.
In addition, the Moon's axis of rotation is tilted slightly so that it does not align with the axis of its orbit. So, yes, the Moon does rotate on its axis.
As far as the dating of Earth and Moon rocks go. Earth is geologically active. Radio-dating of rocks can only go back as far as when that rock cooled from being lava. Since the rock cycle is continuously recirculating crust material, the oldest dated rock found on Earth only sets a lower limit for its age, not an upper one. The Moon lost any interior heat it had much sooner than the Earth, and its oldest rocks haven't had to deal with being recycled and having their radio-dating clocks "reset".
Highlighted
Collision with what .
The Moon shows no such evidence of a collision with Earth .
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Janus58
Valued Senior Member
A body roughly the size of Mars. The name given for this hypothesized planet is "Theia". One possibility is that it was originally located in one of Earth's Lagrange points (L4 or L5), and was perturbed from this position by Venus.
One reason this is thought to be the case is that models show that the collision speed had to be fairly low, which is consistent with something already in an orbit similar to the Earth's.
But where are the scares from this collision on the Moon ? Evidence of this collision are nowhere on the Moon .
Janus58
Valued Senior Member
The Moon wouldn't have been thrown off in one piece but as a bunch of debris, which later collected to form the Moon. The act of collecting together of this material would have involved enough energy, to heat it to molten temps. The molten Moon cooled over time into a spherical shape, and has suffered a great deal of bombardment since then which further shaped it surface. So you wouldn't expect for there to be any type of visible scars on the Moon from that Initial Earth-Theia collision, just the craters, etc that came after the surface cooled.
Fair enough, but I encourage you to try that experiment I mentioned so you can see it happen in real time.
And the debris would have flown off at high speeds in all directions .
And the Earth would have been older or just as old as the Moon , which is not the case . The Moon 160,000,000 yrs. Older .
So the Moon came from Earth ? Disagree the Moon is 160,000,000 older than Earth .
Halc
Registered Senior Member
Quite simple actually: For potential moon M to be captured by planet P, the speed of M relative to P needs to drop below the escape speed of P. So our moon is moving at about 1 km/s, less than the escape speed of 1.44 km/s at that altitude. So it is captured.
Trick is getting any incoming object to do this, which mathematically requires some encounter to slow it since any incoming object by definition must have positive energy and thus is moving at greater than escape speed.
Theia, if coming from a Lagrange point, may well have been slow enough to qualify, but then where is it? A that low speed, it could not have escaped, and I don't think the models have Theia being mostly absorbed by whatever Earth was before that event.
But what of momentum , inertia , how is the inertia of the Mass of the Moon over come , by Earth mass ?
That is Issac's point . The Mass of the Earth is not large enough to overcome the Moons inertia .
Janus58
Valued Senior Member
How the debris spreads after the collision depends on the manner of the collision. Computer models have been applied to this scenario to see what kinds of collision could result in the Moon ending up forming. As I said earlier, this is why, as I said earlier is is suspected that Theia originated from either L4 or L5, as an object starting from there would have the right relative speed. You have no idea as to what the result would be, as you don't have a grasp of the math or physics needed to figure it out.
No. You obviously did not understand or just ignored my previous post on this subject. The Moon is not older than the Earth. The Earth is older than the oldest rocks we can date. As I already stated, the radio-dating clock for rocks starts after the rock has cooled enough to be no longer molten. Rocks on Earth undergo a cycle were magma is forced up in some forming new rock while older rock is force down to form magma again. This cycle takes less time than the age of the Earth. Thus the "oldest rock" on Earth is going to be younger than the Earth itself. The Moon has stopped any geological activity, as it is much smaller than the Earth and lost its internal heat faster. Without an active rock cycle, the Moon would have "older" rocks than the Earth, but this does not make it older.
This is a really bad habit on your part.
1. You base an argument on a claim .
2. Someone explains that the claim is wrong and why.
3. You go right back to using the same claim to support an argument.
Nonsensical nonsense often spouted by yourself.
The Moon orbits the same rate as it rotates...around once every 28 days or so. In the far distant future, the Moon will be about double its current distance, and the Earth's rotational period will be also around 28 days...So not only will the Moon have one side facing the Earth, the Earth will also have one side facing the Moon.
This type of orbital sequence is actually seen elsewhere, mainly with Pluto/Charon system, and other moons of Jupiter and Saturn.
This was also raised by you previously, and you were shown how you took Asimov out of context.
Again for others, all this has been discussed with river before, including his mistaken take on what Asimov is supposed to have thought.
As usual, totally ignorant of the scientific methodology. The scientific modeling you claim as nonsense, is based on all the observational and experimental evidence we have, and has given us theories that are near certain in their makeup and predictions. eg: The BB, SR, GR, Darwinism and the theory of evolution.
According to the evidence and the result of computer modelling, a planet about the size of Mars, that has been dubbed Theia.
Only fools call it the Dark side...It is simply the far side. It undergoes night and day.
Do you learn?? I mean really? Or do you simply go out of your dishonest way to go to any lengths to dispute current mainstream physics?
The same reason the following statement was made by another poster.
No river, you never learn.
The theory of the moon , is that a venus sized object collided with the Earth .
And the debris coalesced into the form of the moon . By gravity .
That's the theory .
Then the Earth has the gravity to capture this object . Which logically the Earth can't , simply because the Earth doesn't have the mass to do so .
And the debris coalesced into the form of the moon . By gravity .
That's the theory .
Then the Earth has the gravity to capture this object . Which logically the Earth can't , simply because the Earth doesn't have the mass to do so .
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