Chemistry says Moon is proto-Earth’s mantle, relocated | Hacker News Reader

Chemistry says Moon is proto-Earth’s mantle, relocated

sciencebulletin.org

160 pointsupen28 comments

Here's the model for which this paper offers support:

http://www.hou.usra.edu/meetings/lpsc2016/pdf/2881.pdf [PDF]

"So another model, proposed in 2015, assumes the impact was extremely violent, so violent that the impactor and Earth’s mantle vaporized and mixed together to form a dense melt/vapor mantle atmosphere that expanded to fill a space more than 500 times bigger than today’s Earth. As this atmosphere cooled, the Moon condensed from it."

I would wonder how long a vapor state would last, before precipitating to liquid, and then freezing into it's final solid form.

I bet the time scales for those phase transitions wouldn't be incalculable, even if gross estimates.

So, if the moon were a vapor bubble suspended in a vacuum, how long would that last? And how long for the heat to radiate out of it?

Sounds like that process would be pretty uniform, and dependent mostly on composition. But the uniformity of the temperature bleed would contribute to the maintenance of a stable orbit.

From fig. 1 on the second page of pdf linked by spenrose below, it looks like vapor cloud was more doughnut/torus-shaped than spherical (due to rotation) and lasted few tens of years.

That is shockingly fast.

Well, that's a comparatively small volume it covered in the grand scheme of things. Just think how quickly a bunch of hair and dust will clump together in the corner of an unswept room.

While the distribution of mass might quickly redistribute itself into a toroidal formation, internally, I think that area of effect (the fuzzy red zone in the diagram) would probably be pretty opaque to visible light. For a period of time, a gas cloud like that would probably have a really interesting appearance.

I'm imagining that, as the hot gases cool off, and condense onto floating debris, the molten/solid debris field will probably look pretty nebulous, and then settle into unstable bands. At that point, I figure the torus shape would be very apparent.

Once the hot gases were gone, I bet it probably took a while for the rest of the debris to get swept up into decaying orbits, and impact on either body (earth/moon).

If they could visualize it with a simulation, it'd probably be fun to watch, and tweak the parameters of the event.

This made me realize that our effort to land on the moon is effectively landing on a relocated proto-Earth's mantle. On a grander scale, landing on any planet in the solar system would probably raise similar thought, but as Moon seems to be directly derived from earth, it will still mean something different for us to land on, say, Mars.

Also ironic that the fastest and easiest way to the center of the Earth (or at least its interior) is to launch into orbit.

Anyone else read this and think that those "moon landing was fake" conspiracy theorists are loving this finding? "Of course the moon rocks are indistinguishable -- they're not actually from the Moon!"

Edit: I'm not one of them. The thought just crossed my mind.

Is there a good theory why there's only one moon, rather than many moons? The diagrams show, "moonlets" - what happened to them? And why didn't this new mass not just collide back into Earth again?

Yes. The dynamics of the situation would have caused the moons to merge (or crash into the Earth).

What would our gravity on earth be if the moon had not been ejected and instead retained as mass? (According to this theory.) Moreover, what equation could I derive that from?

The mass of the Earth is 5.972E24 kg; the moon 7.348E22 kg. Combined, they're 6.945E24 kg, or about 1.2% more massive than the Earh is today.

The change in surface gravity wouldn't be meaningful. Capillary action would still permit tall trees and chemical rockets would still reach escape velocity. Toss Mars or Venus into the Pacific, on the other hand, and a more interesting game develops.

s/6.9/6.0

Note, however, that the surface is also at a slightly larger radius from the center of that increased mass, so the net increase in surface acceleration is less than 1.2%.

[Edit: Note that the moon is less dense than the earth. By my calculations, adding the moon's material to the earth (and keeping it at the moon's density) would increase the earth's radius by 43 km, and (if you accept the parent's 1.2% mass increase figure), the surface acceleration would be 0.998 times the current value.]

The added mass would also increase the size of the Earth, which would reduce the surface gravity. Overall the end result would be something like 0.4% higher surface gravity.

Capillary action is not nearly strong enough to permit tall trees. This is a common misconception. The stronger mechanism is negative pressure, caused by transpiration at the top of the tree, pulling up miniscule strands of water under high tension.

So I vote they call this the "Alderan model"

I recall reading speculation that the core of the impactor (Theia) is Mercury. But nothing is showing up when I search. Anyone else remember that?

> That debris went into orbit, then coalesced to form the Moon. And that raises an intriguing counter-theory: maybe that Mars-size impactor, which planetary scientists call Theia, is the object that became Mercury. If that’s correct, the answer to where Mercury’s rocky outer layer went might not be under our feet after all.

Source: http://time.com/2958731/mercury-peculiar-solar-system/

Thanks.

> Earth, Venus, Mars and asteroids such as Vesta and, perhaps, Lutetia have chondritic bulk compositions with massive silicate mantles surrounding iron cores. Anomalies include Mercury with its abundant metallic iron (about 70% by mass), the Moon with its small iron core, and metal-dominated asteroids. Although a giant impact with proto-Earth can explain the Moon’s small core, a giant impact origin for Mercury is problematic. Such a scenario requires that proto-Mercury was blasted apart with far greater specific energy than required for lunar formation, yet retained substantial volatile elements and did not reaccrete its ejected mantle. Here we present numerical hydrocode simulations showing that proto-Mercury could have been stripped of its mantle in one or more high-speed collisions with a larger target planet that survived intact.

http://www.nature.com/ngeo/journal/v7/n8/full/ngeo2189.html

So now we have evidence that lunar formation involved far greater specific energy than thought. It seems plausible that Theia's core could have survived a near head-on collision with Earth, which vaporized both mantles.

Ok , you read this theories about how moon was initially formed and you think sounds plausible . But then if you think about the math behind full solar eclipse you have to question yourself what are the chances of having it .

Could you unpack this a little bit.

God, I think ;)

Oh...

well :)

The sun and moon appear the same size in Earth's sky because the sun's diameter is about 400 times greater – but the sun is also about 400 times farther away.

So what are the chances of having a satellite that is 400 times smaller than the sun and also being positioned at exactly 1/400 of the distance to the sun , to be able to give us this beautiful ring during solar eclipse?

and yeah guys.. keep down-voting...

What would the chances have to do with the fact of having it? We have eclipses. Nothing about the odds of that configuration has any bearing on that.

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