Question about J White's moon rock composition

[Luke Pemberton]

If the Earth and Moon formed in the same part of the solar nebula they would be expected to have the same oxygen isotopes.  All three pre-Apollo lunar formation models would have predicted it - the sibling and daughter hypotheses would predict the same ratios, the spouse model may have led to a Moon with different oxygen isotopes, although the most likely orbits for capture would be ones that would again have resulted in similar ratios.

What are you trying to say regarding the neutron capture cross sections?  That is way over my head!

My understanding is that oxygen isotope ratios are similar in Earth and lunar samples. Jarrah seizes upon this as proof that the lunar rocks are just Earth rocks. However, what he fails to mention is that the isotope ratios for heavier elements are different for Moon rocks.

Again, my understanding is that the isotope ratio difference for heavier elements is due to neutron capture from cosmic ray irradiation of the lunar surface and secondary neutron production. Elements such as Gadolinium and Samarium appear in the literature as the main fingerprint for isotope differences, and this is not surprising given that their neutron capture cross sections are much larger than oxygen.

http://periodictable.com/Properties/A/NeutronCrossSection.html

ETA: I know you lurk here Blunder, don't cite me as saying that the Moon is a radioactive sea of neutrons as I clearly did not say this anywhere in the above. In fact, you might find this article quite interesting about your Yahoo claims that the moon is a radioactive wasteland.

http://www.universetoday.com/47712/lro-finds-some-surprises-on-the-moon/

[ka9q]

I remember the three leading pre-Apollo hypotheses of the moon's formation: co-formation, capture and fission. As with many things in science, the evidence ultimately ruled them all out.

Yet in a sense they were all correct. Theia co-formed in the same orbit as the earth. It impacted the earth, which is a rather dramatic way of being captured by it. And the impact debris fissioned from the earth to form the moon.

Speaking of the giant impact hypothesis, are there any really good animations of a computer simulation? I'm still having trouble wrapping my brain around the magnitude and violence of such an event.

[ka9q]

You guys seem to have a pretty good grasp of geological chemistry, how planets differentiate and how different kinds of rocks form in different environments. I have a pretty good grasp of basic physics and inorganic chemistry but my geology is really weak. Can you suggest a good introduction?

[frenat]

Speaking of the giant impact hypothesis, are there any really good animations of a computer simulation? I'm still having trouble wrapping my brain around the magnitude and violence of such an event.

https://www.youtube.com/results?search_query=moon+formation

[ka9q]

Thanks, I'm looking at them now. I don't know if any are based on actual simulations of the laws of physics.

These "artist's conceptions" are very pretty, but they tend to be unrealistic; e.g., impacts between small objects are often depicted with unrealistically low velocities. And the collision between the Earth and Theia is so far outside human experience that our intuition about how it looked is probably very wrong.

[Dalhousie]

This is a video of a proper simulation.

[Dalhousie]

You guys seem to have a pretty good grasp of geological chemistry, how planets differentiate and how different kinds of rocks form in different environments. I have a pretty good grasp of basic physics and inorganic chemistry but my geology is really weak. Can you suggest a good introduction?

there are lots of good introductory books on geology, I suggest you look at the recommended text books of local universities teaching in this area.

[Luke Pemberton]

Speaking of the giant impact hypothesis, are there any really good animations of a computer simulation? I'm still having trouble wrapping my brain around the magnitude and violence of such an event.

The impact theory explains a little more than the geology, it is also a good candidate to explain the relatively high angular momentum of the Earth-Moon system.

[Luke Pemberton]

This is a video of a proper simulation.

Thanks for that. For some reason this made my Facebook feed recently, but it appears to be quite old news. Such simulations have shown that the Earth may have had two moons and it could explain the difference between the far and near side of our Moon.

http://www.space.com/12529-earth-2-moons-collision-moon-formation.html

[Luke Pemberton]

Speaking of the giant impact hypothesis, are there any really good animations of a computer simulation? I'm still having trouble wrapping my brain around the magnitude and violence of such an event.

I know, these sort of events are really difficult to imagine. I have problems with the ideas of a supernova and meteor extinction events, such as the one that we believe was responsible for finishing off most of the dinosaurs. I had the same trouble imagining the destructive power of a tsunami until I saw those awful films of the Boxing day tsunami. Such events are akin to trying to put into perspective the size of the universe. I try not to think too much about it and just accept that I will never truly understand the scale.

Another event that has been modelled is the Andromeda (not our Andromeda) and Milky Way collision. Some cosmologists make the prediction that given the distances between stars, the event will not actually be that spectacular in terms of destructive power, instead the galaxies will merge and stabilise into a bigger galaxy. Hard to believe really.

[onebigmonkey]

It's kind of like the ridiculous consonant laden names scifi authors like to give their aliens - you have no hope of reading them, you just have to accept that the shapes are there. Likewise the scale of the universe and the things involved in shaping it - best not to try wrap your head around some of the concepts involved!

When I taught undergraduate geology sat on a mountain side in north Wales I liked to say that our understanding of events is constrained by our longevity and our morphology. The forces that produce u-shaped valleys or pyramidal peaks of folds and faults are no different to things we can experience ourselves, they just go on for longer and are much bigger in scale!

[Luke Pemberton]

It's kind of like the ridiculous consonant laden names scifi authors like to give their aliens - you have no hope of reading them, you just have to accept that the shapes are there. Likewise the scale of the universe and the things involved in shaping it - best not to try wrap your head around some of the concepts involved!

Yup. String theory (or M-theory) is another thing that I can't quite get my head round, at least the 11 dimensionality part. I can picture the concept of strings in the topological structure of space at the quantum level (at least in the sense of popular science writing for the layman in string theory) and how they are explain the unravelling of the four forces of nature, accounting for gravity being so weak. The idea of 11 dimensions is hard to understand visually. However, I can picture 4-space in relativity, it is rather intuitive in the sense of relating time dilation and the simultaneity of events in the Euclidian space I experience.

[Bob B.]

Another event that has been modelled is the Andromeda (not our Andromeda) and Milky Way collision. Some cosmologists make the prediction that given the distances between stars, the event will not actually be that spectacular in terms of destructive power, instead the galaxies will merge and stabilise into a bigger galaxy. Hard to believe really.

There is a lot of empty space out there.  I always somewhat irritated when I see the way Hollywood depicts an asteroid belt.  They have asteroids bouncing of each other and spacecraft dodging them, while in real life asteroids are hundreds of kilometers apart.  Similarly, in a galaxy merger the stars just move through the vast distances in between without too much excitement.

[Dalhousie]

Another event that has been modelled is the Andromeda (not our Andromeda) and Milky Way collision. Some cosmologists make the prediction that given the distances between stars, the event will not actually be that spectacular in terms of destructive power, instead the galaxies will merge and stabilise into a bigger galaxy. Hard to believe really.

There is a lot of empty space out there.  I always somewhat irritated when I see the way Hollywood depicts an asteroid belt.  They have asteroids bouncing of each other and spacecraft dodging them, while in real life asteroids are hundreds of kilometers apart.  Similarly, in a galaxy merger the stars just move through the vast distances in between without too much excitement.

The interstellar dust and gas clouds tend to get excited though....

[Luke Pemberton]

There is a lot of empty space out there.  I always somewhat irritated when I see the way Hollywood depicts an asteroid belt.  They have asteroids bouncing of each other and spacecraft dodging them, while in real life asteroids are hundreds of kilometers apart.  Similarly, in a galaxy merger the stars just move through the vast distances in between without too much excitement.

The interstellar dust and gas clouds tend to get excited though....

Excited yes, but I understand no longer dense enough to produce significant star birth events. It may be that the coalescing of the two galaxies is a bit of a whimper. Happy to be corrected as usual.