An impact between a Mars-sized protoplanet and early Earth is the most widely-accepted origin of the Moon. (NASA/JPL-Caltech)

What’s the Moon Made Of? Earth, Most Likely.

Article Updated: 26 Apr , 2016

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Recent research on lunar samples has shown that the Moon may be made of more Earth than green cheese — if by “green cheese” you mean the protoplanet impactor that was instrumental in its creation.

It’s an accepted hypothesis that Earth’s moon was created during an ancient, violet collision between our infant planet and a Mars-sized world called Theia, an event that destroyed Theia and sent part of Earth’s crust and upper mantle into orbit as a brief-lived ring of molten material. This material eventually coalesced to form the Moon, and over the next 4.5 billion years it cooled, became tidally locked with Earth, accumulated countless craters and gradually drifted out to the respectable distance at which we see it today.

Theia’s remains were once assumed to have been a major contributor to the material that eventually formed the Moon.   Lunar samples, however, showed that the ratio of oxygen isotopes on the Moon compared to Earth were too similar to account for such a formation. Now, further research by a team led by scientists from The University of Chicago shows that titanium isotopes — an element much more refractive than oxygen — are surprisingly similar between the Moon and Earth, further indicating a common origin.

“After correcting for secondary effects associated with cosmic-ray exposure at the lunar surface using samarium and gadolinium isotope systematics, we find that the 50Ti/47Ti ratio of the Moon is identical to that of the Earth within about four parts per million, which is only 1/150 of the isotopic range documented in meteorites,” wrote University of Chicago geophysicist Junjun Zhang, lead author of the paper published in the journal Nature Geoscience on March 25.

If the Moon is more Earth than Theia, then what happened to the original impacting body? Perhaps it was made of heavier stuff that sunk deeper into the Moon, or was assimilated into Earth’s mantle, or got lost to space… only more research will tell.

But for now, you can be fairly sure that when you’re looking up at the Moon you’re seeing a piece of Earth, the cratered remnants of a collision that took place billions of years ago.

See the team’s paper here.

Image credit: NASA / JPL-Caltech

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Zoutsteen
Member
Zoutsteen
April 12, 2012 6:26 AM

I heard this story about a wandering gasgiant that decided to go for a strawl. Who knows, maybe earth had a close encounter with it and broke in pieces.

Denver
Member
Denver
April 12, 2012 2:26 PM

Velikovsky for the win?

Olaf
Member
Olaf
April 12, 2012 4:40 PM

Well if you want to claim such a thing then be prepared to back it up with scientific evidences.

Start with something obvious, how close must such gas giant come in order to make something like Earth break up? How strong would the tidal forces need to be in order to break up Earth?

Denver
Member
Denver
April 12, 2012 6:21 PM

Roche limit, eh?

Olaf
Member
Olaf
April 12, 2012 7:09 PM

Now fill in the numbers, mass and distance of your choice and tell me what you get.

Olaf
Member
Olaf
April 12, 2012 7:09 PM

Now fill in the numbers, mass and distance of your choice and tell me what you get.

Checkers Crossfox
Guest
Checkers Crossfox
April 12, 2012 6:55 PM

Be more likely that a wandering gas giant would destabilize orbits, leading to a collision between bodies, as opposed to actually tearing one apart…

HeadAroundU
Guest
HeadAroundU
April 12, 2012 9:53 AM

Well, it could be made from a similar material right from the beginning and actually heavier material could sunk into Earth and the rest intermixed and created moon. Just throwing some ideas. grin

Simon Donaldson
Guest
April 12, 2012 1:54 PM

IT’S NIBERU! NIBERU! NIBERRRUUUU!

Just thought I’d throw that insane, psycopathic-suggestion out there ^^

That said, maybe it was a massive chunk of radioactive uranium – I hear there’s loads of the stuff around the mantle.
At least… I think it was Uranium…

Either way, No doubt there will be some deep-crust mining operation on the moon in the next thousand years or so, we’ll find out then, or, at least, our descendents will smile

Denver
Member
Denver
April 12, 2012 2:09 PM

I’m sorry, if Theia formed in the vicinity of Earth’s L4 or L5 point, 60 degrees fore and aft, wouldn’t it consist of essentially the same material as the proto-Earth?

Dark Gnat
Member
Dark Gnat
April 12, 2012 3:03 PM

But how do they know it was called Theia? That’s proof that NASA is hiding aliens from us!

/sarcasm

Jessica Frankie
Guest
April 12, 2012 4:27 PM

Interesting. I’ve been always curios about what’s the moon made of. Now I have another curiosity, who made the Universe after all? Were there people years, thousands of years on the moon? Were there people on the moon?
Tons of questions, but the answers are few.

Denver
Member
Denver
April 12, 2012 6:19 PM

Armstrong and Aldrin
Conrad and Bean
Shepard and Mitchell
Scott and Irwin
Young and Duke
Cernan and Schmitt

“were people on the moon”.

Otherwise, I bloody well don’t know what you’re talking about.

Jessica Frankie
Guest
April 16, 2012 12:35 PM

Thanks for your answer. Never thought I’d get so many answers in the first place, but this place is super cool. Now to answer:
I am very curios how many people were on the moon. I really think there is more than we already know. I think there is a conspiracy all over. I think they already have a base on the moon. Probably they will tell everyone after they need enough workers to work on the Moon to make it public.

We are so evolved, it’s nearly impossible someone not to profit on the Moon resources. Nearly impossible. Curios what others have to say about it. It drives me crazy and curios.

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
April 13, 2012 8:40 PM

Don’t you mean “what” made the universe?

Nothing external can make a universe, it is a zero energy system so it is thermodynamically forbidden. It may have tunneled out of an earlier universe which gets around the thermodynamical no-go theorem , a recent paper claim you can’t tunnel out of physics absent spacetime, the easier money goes on that it is part of a larger multiverse which may or may not have been eternal. (If this is too dense I can unpack it later, just ask.)

So no “who” or even likely a “what”. It likely just is.

Jessica Frankie
Guest
April 16, 2012 12:40 PM
Love your answer. Again, never thought I’ll receive so many cool answers around (so I’ll be regular around). My thinking is that the Universe is just a 1, not a 0. I think it’s either a coincidence or a mistake. Or probably just a small atom in another universe or another alien body. But, it’s nearly impossible that this sum of universes, this multiverse to come out of nothing. A flash or something made it. Maybe nothing. I want to understand infinity, but my brain can’t. Maybe math formulas can, but I guess our math is not perfect, neither the whole multiverse works on the math we know. In our math 1+1 = 2, but this does not… Read more »
DrumaSanduma
Guest
DrumaSanduma
April 15, 2012 5:59 PM

Yes, they’re known as the SELENITES grin

Prism2Spectrum
Guest
Prism2Spectrum
April 16, 2012 12:11 AM

___________________________________________

How do you know so much about everything? –
was asked of a very wise and intelligent man; and
the answer was, “By never being afraid or ashamed
to ask questions as to anything of which I was ignorant.”

A child can ask a thousand questions that the wisest
man cannot answer.

– Jacob Abbot (1803-79), American Author.
_________________

There is frequently more to be learned from the
unexpected questions of a child than the discourses of men.

– John Locke (1632-1704), English Philospher.

___________________________________________

Hope these thoughts of great men our of a little encouragement.

You have some good questions.

NoAstronomer
Member
NoAstronomer
April 12, 2012 7:18 PM
Personally I find the notion that the earth and the moon are made of essentially the same stuff completely unsurprising. For a start, as Shootist says both Earth and Theia formed out of the same dust cloud at around the same time. Then we whack both bodies together hard enough that a substantial portion of the Earth is blown into orbit. Presumably much of Theia suffers the same fate. The debris then either falls back to Earth or goes to form the moon. Which it could do as either a completely new body or it could form around the remnants of Theia. Either way the crusts of the two resulting bodies are formed out of the combined debris… Read more »
Ray Fowler
Guest
Ray Fowler
April 12, 2012 7:07 PM

Seems to me that the collision would have been so violent and thorough that the compositions of the Earth & Moon both represent a uniform mixture of what had previously been separate compositions of proto-Earth and Theia.

Ray Fowler
Guest
Ray Fowler
April 12, 2012 7:07 PM

Seems to me that the collision would have been so violent and thorough that the compositions of the Earth & Moon both represent a uniform mixture of what had previously been separate compositions of proto-Earth and Theia.

Ray Fowler
Guest
Ray Fowler
April 12, 2012 7:07 PM

Seems to me that the collision would have been so violent and thorough that the compositions of the Earth & Moon both represent a uniform mixture of what had previously been separate compositions of proto-Earth and Theia.

Ignacio Gonzalez
Guest
Ignacio Gonzalez
April 13, 2012 8:35 AM

a VIOLET collision?

JunoVidor
Member
JunoVidor
April 13, 2012 12:39 PM

Just read “violent collision”, ok?
I was told once this is a weblog page only rather than the page of a book in astronomy. Fair enough.

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
April 13, 2012 8:35 PM
To add to the list of hypotheses: – That the impactor may have equilibrated with Earth has been the most recent explanation, offered in my astrobiological books. “A more recent proposal is that the moon formed much later than previously thought from the impact of a large asteroid creating the moon primarily from debris from earth. The formation of the moon in this hypothesis occurs 60-140 million years after the formation of the solar system. The age of the moon had been previously thought to be 4.527 ± 0.010 billion years ago.[33] The impact would have created a magma ocean on Earth and the proto-moon with both bodies sharing a common plasma metal vapour atmosphere. The shared metal… Read more »
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