What Are the Leading Theories Behind the Moon's Origin and Inclination?

[Mammo]

There is currently a number of proposals for the evolution or origin of the Moon. It has an unusually high inclination to the Earth's equatorial plane and a low inclination to the ecliptic, which has prompted varied speculation. (See Wikipedia Moon). I was particularly interested in the following report Moon's Orbital Inclination Pumped up by a Passing Protoplanet with Mars Size 2004. Is it not also possible that the Moon's orbital inclination has been changed by a Mars sized NEO fly-by in the recent past? This would seem just as probable, and would it not give credibility to the alternatives to the giant-impact hypothesis for it's creation?

 

[Vanadium 50]

Is it not also possible that the Moon's orbital inclination has been changed by a Mars sized NEO fly-by in the recent past?

Not likely. Starting with the obvious, where is this extra planet hiding?

 

[Mammo]

Not likely. Starting with the obvious, where is this extra planet hiding?

Maybe not quite Mars sized, but there are a lot of large bodies existing outside the orbit of Neptune. See Trans-Neptunian object Wikipedia (source of picture)

 

[Vanadium 50]

Maybe not quite Mars sized

Not even close. Eris is about 2% of Mars. So where is this Planet X?

 

[Mammo]

Not even close. Eris is about 2% of Mars. So where is this Planet X?

I'm not a closet Planet X believer. What I'm saying is that this object could have been comparable in size to the Moon.

 

[Vanadium 50]

Well, your object is surely shrinking. The Moon is only one tenth the size of Mars. It's still 4 times more massive than Eris. So I still don't see where an object this big could be hiding.

How recent is recent?

 

[Mammo]

Well, your object is surely shrinking. The Moon is only one tenth the size of Mars. It's still 4 times more massive than Eris. So I still don't see where an object this big could be hiding.

How recent is recent?

The near-miss could have occurred anytime since it's formation/capture. It may have even happened more than once. It is the closeness of the encounter which is of primary importance. The size of the given trans-Neptunian objects above justifiy the possibility of such an event. Surely it's common sense? I'm not saying that it definitely did happen, just that it may have.

 

[The Dagda]

I prefer the collision event Early in Earth's history, just seems to have more going for it, that way the moon could end up practically anywhere, using Occam's razor at least it seems to be neater.

 

[Mammo]

I prefer the collision event Early in Earth's history, just seems to have more going for it, that way the moon could end up practically anywhere, using Occam's razor at least it seems to be neater.

I agree that some extra circumstantial evidence would be needed to popularize the notion.

 

[Vanadium 50]

The near-miss could have occurred anytime since it's formation/capture.

But that was 4 billion years ago, so now you've moved past "recent".

 

[Mammo]

But that was 4 billion years ago, so now you've moved past "recent".

I'm emphasising the fact that the original concept of a NEO deflection encounter with the Moon by a proto-planet around the time of formation can easily be applied to a closer encounter with a smaller object anytime since then.

 

[Arch2008]

From your report link:
“We also found that such a fly-by encounter is likely to occur on timescales 10^7 - 10^8 years after the lunar-forming impact.”

They aren’t even proposing an alternative to the lunar forming impact event. They are proposing that an NEO caused the Moon’s “unusually high inclination to the Earth's equatorial plane and a low inclination to the ecliptic” after the impact event. So what they discuss or you propose does not give credibility to the alternatives to the giant-impact hypothesis for the Moon’s creation at all.

 

[granpa]

isnt the moons orbit in the ecliptic?

edit:The mean inclination of the lunar orbit to the ecliptic plane is 5.145°.
also the angle between the ecliptic and the lunar equator is always 1.543°.

 

[Mammo]

From your report link:
“We also found that such a fly-by encounter is likely to occur on timescales 10^7 - 10^8 years after the lunar-forming impact.”

They aren’t even proposing an alternative to the lunar forming impact event. They are proposing that an NEO caused the Moon’s “unusually high inclination to the Earth's equatorial plane and a low inclination to the ecliptic” after the impact event. So what they discuss or you propose does not give credibility to the alternatives to the giant-impact hypothesis for the Moon’s creation at all.

Wikipedia Moon states:

Fission hypothesis:..the process should have resulted in the Moon's orbit following Earth's equatorial plane. This is not the case.
Capture hypothesis: Other speculation has centered on the Moon being formed elsewhere and subsequently being captured by Earth's gravity.
Co-formation hypothesis : The co-formation hypothesis proposes that the Earth and the Moon formed together at the same time and place from the primordial accretion disk.

A major deficiency in all these hypotheses is that they cannot readily account for the high angular momentum of the Earth–Moon system.

Therefore the above suggestion does add to the credibility of the other three candidates. These still may have potential problems which would need to be resolved.

* I've just found some circumstantial evidence to add to the idea: http://www.sciencemag.org/cgi/content/full/313/5787/652

 

[granpa]

isnt it much more likely that it was the Earth that had its axis shifted from the ecliptic by an impact after the moon had already formed?

as opposed to the idea that the Earth had its axis shifted then the moon formed then the moon had its orbit and its axis both shifted back to the ecliptic.

 

[Arch2008]

Actually the entire excerpts are:
“Fission hypothesis
Early speculation proposed that the Moon broke off from the Earth's crust because of centrifugal forces, leaving a basin – presumed to be the Pacific Ocean – behind as a scar.[41] This idea, however, would require too great an initial spin of the Earth; and, even had this been possible, the process should have resulted in the Moon's orbit following Earth's equatorial plane. This is not the case. “
And:
“Co-formation hypothesis
The co-formation hypothesis proposes that the Earth and the Moon formed together at the same time and place from the primordial accretion disk. The Moon would have formed from material surrounding the proto-Earth, similar to the formation of the planets around the Sun. Some suggest that this hypothesis fails adequately to explain the depletion of metallic iron in the Moon.
A major deficiency in all these hypotheses is that they cannot readily account for the high angular momentum of the Earth–Moon system.[43]”

The “too great an initial spin” for fission and “that this hypothesis fails adequately to explain the depletion of metallic iron in the Moon” for co-formation are the major scientific deficiencies and an NEO doesn’t explain this away. I think that the Wiki author should have said “A common deficiency in all these hypotheses…”

 

[granpa]

the issue of too much angular momentum is similar to the unsolved question of how material is able to fall into AGN's.

here is a nice paper on the fission hypothesis:
http://adsabs.harvard.edu/full/1980LPSC...11.1931B

 

[Mammo]

Actually the entire excerpts are:
“Fission hypothesis
Early speculation proposed that the Moon broke off from the Earth's crust because of centrifugal forces, leaving a basin – presumed to be the Pacific Ocean – behind as a scar.[41] This idea, however, would require too great an initial spin of the Earth; and, even had this been possible, the process should have resulted in the Moon's orbit following Earth's equatorial plane. This is not the case. “
And:
“Co-formation hypothesis
The co-formation hypothesis proposes that the Earth and the Moon formed together at the same time and place from the primordial accretion disk. The Moon would have formed from material surrounding the proto-Earth, similar to the formation of the planets around the Sun. Some suggest that this hypothesis fails adequately to explain the depletion of metallic iron in the Moon.
A major deficiency in all these hypotheses is that they cannot readily account for the high angular momentum of the Earth–Moon system.[43]”

The “too great an initial spin” for fission and “that this hypothesis fails adequately to explain the depletion of metallic iron in the Moon” for co-formation are the major scientific deficiencies and an NEO doesn’t explain this away. I think that the Wiki author should have said “A common deficiency in all these hypotheses…”

You have deliberately left out the Capture Hypothesis from Wikipedia Moon:

Capture hypothesis
Other speculation has centered on the Moon being formed elsewhere and subsequently being captured by Earth's gravity.[42] However, the conditions believed necessary for such a mechanism to work, such as an extended atmosphere of the Earth in order to dissipate the energy of the passing Moon, are improbable.

but..

Wikipedia atmosphere:

The history of the Earth's atmosphere prior to one billion years ago is poorly understood; it is an active area of scientific research. The following discussion presents a plausible scenario.