Question Earth Moon Origin

[Catastrophe]

Inmymind

"One problem is the Moon's iron core is only 1% and Earth's is 13%. If they formed from separate parts of the same cloud they would have the same iron amounts"

Is this not well known? Without checking, I seem to recall that the larger Earth lost only crust and some mantle, whereas the Moon (or precursor) lost also some core to Earth (successor)

Cat

 

[billslugg]

I can see in the videos the interloper's iron core melds with proto-Earth's, then the two bodies mantles mix together and a large amount shoots into space and forms a ring which eventually makes the Moon.

 

[Catastrophe]

Inmymind:

I have had a quick look through my books on the Moon, and those on the Solar System which have appreciable sections on the Moon. The most interesting so far has been one of the older books "Encyclopaedia of the Solar System", Academic Press, 1999.

On page 274, there is a computer simulation of the origin of the Moon by a glancing impact of a body larger than Mars with the early Earth. There are 6 diagrams covering impact plus 1 minute, 10 minutes, 1 hour, 2.3 hours, 4 hours and 24 hours. First contact after 1 minute. After 10 minutes shows impactor mantle just reach ing Earth core, and Earth mantle just reaching impactor core. After 1 hour shows impactor, with greatly reduced core, having separated from Earth. This clearly suggests that some of impactor core transferred to Earth core. Something between 10 minutes and 1 hour would have been interesting. Does anyone else have simulations?

The relevant part of the caption reads "Both the impactor and the Earth have differentiated into a metallic core and rocky silicate mantle. Following the impact, the mantle of the impactor is ejected into orbit. The metallic core* of the impactor clumps together and falls into the Earth within about 4 hours. . . . . . . Most terrestrial mantle material ejected by the impact follows a ballistic trajectory and is reaccreted by the Earth. The metal-poor, low density, Moon is thus derived mainly from the silicate mantle of the impactor" . . . . . . (edit) * and some of the metallic core from the impactor.

Hence the discrepancy.

Cat

 

[Catastrophe]

Here, again, from Wiki "Giant-Impact Hypothesis":

• The Moon has a relatively small iron core, which gives it a much lower density than Earth. Computer models of a giant impact of a Mars-sized body with Earth indicate the impactor's core would likely penetrate deep into Earth and fuse with its own core. This would leave the Moon, which was formed from the ejecta of lighter crust and mantle fragments that went beyond the Roche limit and were not pulled back by gravity to re-fuse with Earth, with less remaining metallic iron than other planetary bodies.

Cat