Siamese Planet?

[DrmDoc]

News of the day, Earth comprises the merged remains of Theia. According to a recently published article in Science, Theia--the Mars sized planet at first believed to have caused our Moon's creation through a "glancing" impact with Earth about 4.6 billion years ago--is now believed to have directly impacted and completely merged with Earth, which "indistinguishable" oxygen isotopic studies appear to suggest. Could there be another explanation for Earth/Moon shared isotopic profile? I welcome your thoughts.

[Robittybob1]

News of the day, Earth comprises the merged remains of Theia. According to a recently published article in Science, Theia--the Mars sized planet at first believed to have caused our Moon's creation through a "glancing" impact with Earth about 4.6 billion years ago--is now believed to have directly impacted and completely merged with Earth, which "indistinguishable" oxygen isotopic studies appear to suggest. Could there be another explanation for Earth/Moon shared isotopic profile? I welcome your thoughts.

My argument go like this:

Take the asteroids of the Asteroid Belt I would guess that they all have a similar isotopic profiles too due to the fact they were all accreted from the same region of the protoplanet disc.

Now if that is accepted and if the Earth and Theia were accreted from a region of a thoroughly mixed (hence isotopically similar) region of the protoplanetary disc that could be the reason they are identical more so than the potential collision between the two bodies.

I have always advocated the Moon was captured by the Earth. OK I read that news article and thought that it still hasn't eliminated co-accretion from the same protoplanetary region plus or minus a collision.

[DrmDoc]

My argument go like this:

Take the asteroids of the Asteroid Belt I would guess that they all have a similar isotopic profiles too due to the fact they were all accreted from the same region of the protoplanet disc.

Now if that is accepted and if the Earth and Theia were accreted from a region of a thoroughly mixed (hence isotopically similar) region of the protoplanetary disc that could be the reason they are identical more so than the potential collision between the two bodies.

I have always advocated the Moon was captured by the Earth. OK I read that news article and thought that it still hasn't eliminated co-accretion from the same protoplanetary region plus or minus a collision.

I agree; why is there this seeming presumption that Earth and Theia would not have the same oxygen isotopic profile? What is the argument or evidence supporting an initial distinction between the two planets? If the original isotopic distinctions between the planets remain undetermined, shouldn't the "glancing" impact theory remain equally as likely as the newly theorized direct impact? Regarding the idea of an Earth captured Moon, how does that align with the Moon's widening orbit from its inception?

[Robittybob1]

I agree; why is there this seeming presumption that Earth and Theia would not have the same oxygen isotopic profile? What is the argument or evidence supporting an initial distinction between the two planets? If the original isotopic distinctions between the planets remain undetermined, shouldn't the "glancing" impact theory remain equally as likely as the newly theorized direct impact? Regarding the idea of an Earth captured Moon, how does that align with the Moon's widening orbit from its inception?

Thanks. Well the concept of tidal acceleration and deceleration is simply and primarily dependent on the rates of orbit compared to the rate of spin.

If the Moon orbits the Earth slower than the Earth spins on its axis (day length) there will be tidal acceleration and if the orbit (lunar month) is less than the day length it will decelerate (come in closer to the Earth)

 

I had proposed some years ago, the Moon upon initial capture orbited the Earth faster than the Earth's day length. It is complicated for the mass of the Earth has to be varied to allow this. Then there was a period they stopped approaching each other and then later as the Earth's volatile mass decreased still further and the Earth's gravitational pull decreased the Moon started its widening orbit to be in the position it is today. I called this the Yo-yo Moon Capture hypothesis.

 

Some of you may be aware of this hypothesis already.

Edited February 5, 2016 by Robittybob1

[pavelcherepan]

I have always advocated the Moon was captured by the Earth. OK I read that news article and thought that it still hasn't eliminated co-accretion from the same protoplanetary region plus or minus a collision.

 

Of all the satellites in the Solar System Moon is the most massive in relation to its host planet. It is highly unlikely that Earth would've been able to capture the Moon. It's possible but it would require an extremely precise conditions which are not very likely to have happened.

 

 

 

News of the day, Earth comprises the merged remains of Theia.

 

Why is this news? This hypothesis has been around for a while.

 

 

 

Theia--the Mars sized planet at first believed to have caused our Moon's creation through a "glancing" impact with Earth about 4.6 billion years ago--is now believed to have directly impacted and completely merged with Earth, which "indistinguishable" oxygen isotopic studies appear to suggest. Could there be another explanation for Earth/Moon shared isotopic profile?

 

Actually, from what I remember same oxygen isotopic ratios have for a long time been an argument against the giant collision hypothesis, because if Theia indeed was formed in a different region of SS then it's highly unlikely that it would have exactly the same O isotope ratios as we see on the Earth based on what we know about isotopic ratios of other planets and asteroids.

 

http://www.psrd.hawaii.edu/Dec01/Oisotopes.html

 

The recent take on this issue is that modelling shows that after a collision for a short while (some hundreds of years) Earth will be surrounded with a plasma ring which included bits of the first atmosphere (and potentially hydrosphere) and rock material that's been evaporated in the impact. Debris that would later coalesce into Moon was within this ring and it allowed for material exchange between Earth and Moon and as a result the isotopic ratios are almost identical.

 

 

 

Take the asteroids of the Asteroid Belt I would guess that they all have a similar isotopic profiles too due to the fact they were all accreted from the same region of the protoplanet disc.

 

Do you just guess or do they really have same isotopic ratios? Studies of meteorites seem to show that they normally don't have same ratios and can vary by large amounts especially in hydrogen/deuterium isotopes.

 

http://www.lpi.usra.edu/meetings/ipm2012/pdf/1030.pdf

 

 

 

I agree; why is there this seeming presumption that Earth and Theia would not have the same oxygen isotopic profile?

 

Because so far it seems like isotopic profile is more or less unique to different bodies of SS. There might be some similarities in one or two elements, but the entire profile is generally quite unique.

 

 

 

I had proposed some years ago, the Moon upon initial capture orbited the Earth faster than the Earth's day length. It is complicated for the mass of the Earth has to be varied to allow this. Then there was a period they stopped approaching each other and then later as the Earth's volatile mass decreased still further and the Earth's gravitational pull decreased the Moon started its widening orbit to be in the position it is today. I called this the Yo-yo Moon Capture hypothesis.

 

Can you give a link to a paper on this theory?

[DrmDoc]

Why is this news? This hypothesis has been around for a while.

Indeed; however, from my reading of the article, the prevailing hypothesis has been an indirect, less energetic "glancing" collision rather than what is now indicated by current research, which suggests a direct, more highly energetic impact. The glancing theory infers our Moon as predominately comprising the remnants of Theia rather than a homogenized version of both Earth and Theia as the article purports based isotopic research.

Edited February 5, 2016 by DrmDoc

[pavelcherepan]

Indeed; however, from my reading of the article, the prevailing hypothesis has been an indirect, less energetic "glancing" collision rather than what is now indicated by current research, which suggests a direct, more highly energetic impact. The glancing theory infers our Moon as predominately comprising the remnants of Theia rather than a homogenized version of both Earth and Theia as the article purports based isotopic research.

 

The article is behind a paywall so I can only see the abstract, but it doesn't say anything about a "direct" collision, it says:

 

 

 

our results favor vigorous mixing during the giant impact and therefore a high-energy, high-angular-momentum impact.

 

Would you care to explain how a direct impact is a higher angular momentum collision compared to a glancing blow? Or simply how can a direct impact be a high angular momentum collision?

Edited February 6, 2016 by pavelcherepan

[DrmDoc]

 

The article is behind a paywall so I can only see the abstract, but it doesn't say anything about a "direct" collision, it says:

 

 

Would you care to explain how a direct impact is a higher angular momentum collision compared to a glancing blow? Or simply how can a direct impact be a high angular momentum collision?

 

Well, here is a link to the January 28th press announcement from the UCLA team behind this latest version of Earth/Theia impact. The article is titled "Moon was produced by a head-on collision between Earth and a forming planet". Enjoy!

[pavelcherepan]

 

Well, here is a link to the January 28th press announcement from the UCLA team behind this latest version of Earth/Theia impact. The article is titled "Moon was produced by a head-on collision between Earth and a forming planet". Enjoy!

 

I believe that one of the great wins of Giant Impact hypothesis in its current most accepted form is that it does a really good job in explaining angular momentum of Earth-Moon system. The article you've linked is very basic and to me it seems like the "direct impact hypothesis" will have a hard time explaining why angular momentum is in its current shape.

 

Also, there are some difficulties with the current model that the new version will also have troubles explaining, for example:

 

 

1. The presence of volatiles such as water trapped in lunar basalts is more difficult to explain if the Moon was caused by an impact that would entail a catastrophic heating event.

2. The iron oxide (FeO) content (13%) of the Moon, which is intermediate between Mars (18%) and the terrestrial mantle (8%), rules out most of the source of the proto-lunar material from the Earth's mantle.

[Robittybob1]

 

Of all the satellites in the Solar System Moon is the most massive in relation to its host planet. It is highly unlikely that Earth would've been able to capture the Moon. It's possible but it would require an extremely precise conditions which are not very likely to have happened.

 

 

Why is this news? This hypothesis has been around for a while.

 

 

Actually, from what I remember same oxygen isotopic ratios have for a long time been an argument against the giant collision hypothesis, because if Theia indeed was formed in a different region of SS then it's highly unlikely that it would have exactly the same O isotope ratios as we see on the Earth based on what we know about isotopic ratios of other planets and asteroids.

 

http://www.psrd.hawaii.edu/Dec01/Oisotopes.html

 

The recent take on this issue is that modelling shows that after a collision for a short while (some hundreds of years) Earth will be surrounded with a plasma ring which included bits of the first atmosphere (and potentially hydrosphere) and rock material that's been evaporated in the impact. Debris that would later coalesce into Moon was within this ring and it allowed for material exchange between Earth and Moon and as a result the isotopic ratios are almost identical.

 

 

 

Do you just guess or do they really have same isotopic ratios? Studies of meteorites seem to show that they normally don't have same ratios and can vary by large amounts especially in hydrogen/deuterium isotopes.

 

http://www.lpi.usra.edu/meetings/ipm2012/pdf/1030.pdf

 

 

Because so far it seems like isotopic profile is more or less unique to different bodies of SS. There might be some similarities in one or two elements, but the entire profile is generally quite unique.

 

 

Can you give a link to a paper on this theory?

Did these all those meteorites come from the Asteroid Belt? I'm taking a guess that the objects in the Asteroid belt predominantly \ accreted from the material in their vicinity, material that had been thoroughly mixed within that region prior to accretion. It is a prediction that may or may not be confirmed in due time.

 

There was no paper written up about the Yo-yo Moon Capture theory, for it was tentative hypothesis that developed from a 2 year project over on another forum and the ideas were developed there.

It ended up having a lot of useful features IMO. All these things which were completely out of my scope to verify but I have kept an eye on developments and this latest news item being discussed here was a challenge but in the interim I don't feel it negates Moon capture either.

 

If you say "the Earth is highly unlikely to have captured the Moon" that is because of our current concept of what the early Earth was like limits us. If it was like a water world Earth as some of the other planets found during the Kepler Mission this objection is overcome somewhat.

I wouldn't say any of the concepts involved are easy to comprehend but in the end there was a set of ideas that I believe fitted the evidence so far.

Now that I have retirement to look forward to it is a possibility to refresh the ideas and maybe write up a paper.

[pavelcherepan]

 

 

I'm taking a guess that the objects in the Asteroid belt predominantly \ accreted from the material in their vicinity, material that had been thoroughly mixed within that region prior to accretion. It is a prediction that may or may not be confirmed in due time.

 

That's a rather wild guess. Main asteroid belt extends between ~1.5 and 5 AU and so covers an area (projected on ecliptic) of over 70 AU². It also includes objects with circular orbits, highly elliprical orbits and a wide range in between. There's also no studies that show that material could've been mixed and homogenised in that entire part of Solar system. Studies of meteorites and asteroids show that they're quite variable in composition.

 

From what we know this prediction can already be shown to be wrong to a high degree of accuracy.

 

 

 

There was no paper written up about the Yo-yo Moon Capture theory, for it was tentative hypothesis that developed from a 2 year project over on another forum and the ideas were developed there.

 

Do you at least have a link to that discussion?

 

 

 

If you say "the Earth is highly unlikely to have captured the Moon" that is because of our current concept of what the early Earth was like limits us. If it was like a water world Earth as some of the other planets found during the Kepler Mission this objection is overcome somewhat.

 

Our idea of what early Earth was like is based on empirical evidence and modelling. Your wild guesses on the other hand are not.

 

EDIT:

 

I had a look around and found several papers by Andreas Reufer et al. that DrmDoc's link has mentioned. That's what it says for example in their paper "A hit and run Giant Impact scenario":

 

 

The best runs coming close to matching the constraints 157 (cC03 and cC06) are obtained using impact angles of 32.5° and 35° and velocities of 1.25 and 1.20 vesc, 158 , resulting in 54% and 56% of the silicate material deriving from the target, and δfT thus 159 increasing to -35% and -37% compared to -66% in the reference run of the canonical case.

 

which is somewhat different to a standard idea, but 32-35^o angle is far from a "direct impact". Nowhere in their paper they even mention simulations of collision for an angle higher than 35 degrees.

Edited February 6, 2016 by pavelcherepan

[Robittybob1]

 

That's a rather wild guess. Main asteroid belt extends between ~1.5 and 5 AU and so covers an area (projected on ecliptic) of over 70 AU². It also includes objects with circular orbits, highly elliprical orbits and a wide range in between. There's also no studies that show that material could've been mixed and homogenised in that entire part of Solar system. Studies of meteorites and asteroids show that they're quite variable in composition.

 

From what we know this prediction can already be shown to be wrong to a high degree of accuracy.

 

 

Do you at least have a link to that discussion?

 

 

Our idea of what early Earth was like is based on empirical evidence and modelling. Your wild guesses on the other hand are not.

I'll have to look into that again. It was a good point you have raised. Yes there is a link and I'll email it to you for the thread was rather chaotic and on the whole not such a good read. It needs to be rewritten at some stage.

The models change with time. I am open to changing my view for sure.

[DrmDoc]

 

I believe that one of the great wins of Giant Impact hypothesis in its current most accepted form is that it does a really good job in explaining angular momentum of Earth-Moon system. The article you've linked is very basic and to me it seems like the "direct impact hypothesis" will have a hard time explaining why angular momentum is in its current shape.

 

Also, there are some difficulties with the current model that the new version will also have troubles explaining, for example:

 

I agree, but there's still the question of those "indistinguishable" isotopic results. Could it be that their study results are based on Moon rocks not obtained through core sampling? Isn't it likely that samples closer to the Moon's core would yield rocks more reflective of Theia's distinctive profile thus validating the prevailing theory?

Edited February 6, 2016 by DrmDoc

[pavelcherepan]

I'll have to look into that again. It was a good point you have raised. Yes there is a link and I'll email it to you for the thread was rather chaotic and on the whole not such a good read. It needs to be rewritten at some stage.

The models change with time. I am open to changing my view for sure.

 

Just like I told you in a PM, you've sent me a link to a 236-page (!!!) discussion started by you where you were arguing that life originated on Mercury. I'm not planning on wasting my time browsing through this pile of rubbish. I you have a link to a particular part where it talks about formation of the Moon (for whatever reason) then please do provide it and hopefully it will contain not just random rambling but some calculations or modelling too.

 

I agree, but there's still the question of those "indistinguishable" isotopic results. Could it be that their study results are based on Moon rocks not obtained through core sampling? Isn't it likely that samples closer to the Moon's core would yield rocks more reflective of Theia's distinctive profile thus validating the prevailing theory?

 

This is just a pure speculation which we'll be only able to confirm/reject when we get some real data. At the moment all the samples collected from the Moon itself by Apollo missions and soviet Luna crafts came from the surface. Even lunar meteorites found on the Earth are still mostly from the crust and don't give any insights on the isotope content of mantle.

 

Still, regardless of the type of collision, whether it was a glancing blow or a more direct impact that formed ejecta that coalesced into the Moon, our satellite should've been in a molten state during coalescence and early life, which should result in relatively good mixing of Theia and Earth-originating materials. Then you could potentially explain the isotopic similarities if the crust had solidified relatively quickly and it mostly was composed of Earth material. That seems rather unlikely, though.

 

I do like the hypothesis by several authors, where it was suggested that "the Earth-Moon isotopic similarity is the result of isotopic re-equilibration between the terrestrial magma ocean and the circum-terrestrial disk formed in the Giant Impact, via a common silicate vapor atmosphere".

 

http://arxiv.org/ftp/arxiv/papers/1012/1012.5323.pdf

 

NB: Papers on Cornell University site have real weird formatting.

 

On the other hand the authors of the new version of Giant Impact hypothesis, which I will refer to as "slightly more direct impact" in a paper discuss various theories of Moon formation and dismisses the above idea based on papers by several other authors:

 

 

Unfortunately, this elegant solution to the isotopic conundrum seems to be problematic for several reasons (e.g., Melosh, 2010; Salmon & Canup, 2012; Pahlevan & Stevenson, 2012; Nakajima and Stevenson, 2014). We will therefore neglect the effects of such re-equilibration for the purpose of this article.

 

http://arxiv.org/ftp/arxiv/papers/1410/1410.3819.pdf

http://arxiv.org/pdf/1210.0932v1.pdf

http://arxiv.org/pdf/1401.3036v1.pdf

 

So it's still a pretty hot debate around the formation of the Moon and hopefully we'll hear some more new and exciting ideas soon.

 

EDIT:

 

Robittybob1 did come back to me with a link to his theory. It's here if anyone's interested.

 

There Robitty argues with himself (apparently by now everyone else got tired of this nonsense and left) for 10-12 posts exploring things like that the original Earth was 42 times the mass of the current one and the majority of it was water which then all was blown away by solar wind because iron core of the Moon disrupted Earth's magnetic field.

 

I'm not lying! That's really what it says there!

 

Also, there are no calculations or any sign that it's all not just a figment of Robitty's imagination.

Edited February 6, 2016 by pavelcherepan

[Ophiolite]

Take the asteroids of the Asteroid Belt I would guess that they all have a similar isotopic profiles too due to the fact they were all accreted from the same region of the protoplanet disc.

You could guess, or you could do some research on the matter. I look forward to your amended posts.

[swansont]

 

There was no paper written up about the Yo-yo Moon Capture theory, for it was tentative hypothesis that developed from a 2 year project over on another forum and the ideas were developed there.

 

!

Moderator Note

Then it does not belong in a mainstream thread (i.e. it belongs in speculations), and you've been here long enough to know the rules.

 

OT responses have been hidden

[DrmDoc]

This is just a pure speculation which we'll be only able to confirm/reject when we get some real data. At the moment all the samples collected from the Moon itself by Apollo missions and soviet Luna crafts came from the surface. Even lunar meteorites found on the Earth are still mostly from the crust and don't give any insights on the isotope content of mantle.

 

Still, regardless of the type of collision, whether it was a glancing blow or a more direct impact that formed ejecta that coalesced into the Moon, our satellite should've been in a molten state during coalescence and early life, which should result in relatively good mixing of Theia and Earth-originating materials. Then you could potentially explain the isotopic similarities if the crust had solidified relatively quickly and it mostly was composed of Earth material. That seems rather unlikely, though.

 

I do like the hypothesis by several authors, where it was suggested that "the Earth-Moon isotopic similarity is the result of isotopic re-equilibration between the terrestrial magma ocean and the circum-terrestrial disk formed in the Giant Impact, via a common silicate vapor atmosphere".

 

http://arxiv.org/ftp/arxiv/papers/1012/1012.5323.pdf

 

NB: Papers on Cornell University site have real weird formatting.

 

On the other hand the authors of the new version of Giant Impact hypothesis, which I will refer to as "slightly more direct impact" in a paper discuss various theories of Moon formation and dismisses the above idea based on papers by several other authors:

 

 

http://arxiv.org/ftp/arxiv/papers/1410/1410.3819.pdf

http://arxiv.org/pdf/1210.0932v1.pdf

http://arxiv.org/pdf/1401.3036v1.pdf

 

So it's still a pretty hot debate around the formation of the Moon and hopefully we'll hear some more new and exciting ideas soon.

 

I agree; as you've observed, there are several plausible explanations that we cannot confirmed without more complete samplings or data. Although, like you, I do favor some "isotopic re-equilibration" as most likely. So, perhaps, it's indeed a bit too early to make certain definitive declarations regarding Earth-Theia impact.