National Geographic News
An illustration of the moon being formed.

This illustration shows the collision between Earth and a smaller planet that formed the moon.

ART BY DANA BERRY. SOURCE: ROBIN CANUP, SWRI

Dan Vergano

National Geographic

Published June 5, 2014

Newly analyzed lunar rocks have revealed the first direct evidence of the ancient smashup that created the moon, bolstering a long-held theory.

The rocks were gathered by astronauts on NASA's Apollo missions. But newer scanning electron microscopes have now allowed scientists to detect in them the first chemical traces of the Mars-size planet thought to have blasted the proto-Earth around 4.5 billion years ago. (Related: "First Explorers on the Moon.")

When the ancient planet, Theia, smashed into Earth, it blasted debris into space. The moon formed out of that debris. Planetary scientists first came up with this theory in the wake of the July 20, 1969, Apollo moon landing, offering an explanation for why our world has such a massive moon. (See: "It All Began in Chaos.")

In Brief

A team led by Daniel Herwartz of Germany's Georg-August-Universität Göttingen reported the new findings about Theia on Thursday in the journal Science. (Related: "Moon 101.")

"If the moon formed predominantly from the fragments of Theia, as predicted by most numerical models, the Earth and Moon should differ," says the study.

Earlier looks at moon rocks hadn't been detailed enough to reveal any difference in the lunar chemistry between them and rocks from the Earth. But this team found a small but significant difference—about 12 parts per million more of a heavier kind of oxygen atom in the moon rocks—that serves as a fingerprint of Theia.

Rogue Planet

The early solar system was a shooting gallery, Herwartz notes, with planets spun out of a disk of dusty material swirling around the young sun that occasionally smacked into each other.

"I think that Theia and the proto-Earth formed in the same region of the protoplanetary disk, more or less from the same material," Herwartz says by email. He thinks roughly 30 to 50 percent of the moon might be Theia.

If Theia was particularly enriched with the heavier kind of oxygen atom, an isotope called oxygen-17, then it might make up less than 30 percent of the moon, he adds.

One outside alternative is that Theia and Earth were chemically identical, and that Earth was later hit by a comet or asteroid that carried a lot of water—proto-oceans—which rearranged Earth's oxygen chemistry.

"This is possible, but unlikely," Herwartz says. "If this was the case, however, the material that was added to the Earth (after the formation of the Moon) must have been very exotic," he says. Meteorites with just such an exotic composition, he adds, must also have been rich in water.

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45 comments
بركات لطيف
بركات لطيف

I think that in binging when the big bang , had many explosive hipping and the earth and stars to form great in galaxy.  .   

Thomas Eubank
Thomas Eubank

Collisions are essentially instantaneous, accretion of the resulting debris takes place over periods of time impossible for us short-lived human beings to comprehend. The near infinity of time and infinitesimally small components of matter taken together have produced a universe that will never cease to confound us.   BTW, The Theia speculation seems right on considering the facts.

Steven Waters
Steven Waters

OK this is all well and good but how do we get two perfectly round planets out of a massive collision. There isn't even any signs of a whimper of a massive hit that would have left at least some evidence of it being big enough to breakup a planet.

H MEEHAN
H MEEHAN

So where is the other half of Theia?

Marty Miller
Marty Miller

The Theians have been on vacation and now they are back and fairly well pissed off!

Kun Hadi
Kun Hadi

Is there any evidence of real happening a planet smashes into other planet in the process, somewhere else in universe?

Paul Vc
Paul Vc

We should ask Sheldon Cooper about it

Steve White
Steve White

Yeah, Theia.  So they can call the inhabitants Tehians in the blockbuster movie.

This is a non-scientific theory.  It was meant to explain one curious fact -- the disparity of ratios of elements between the Earth and Moon, and fair enough.  But it raises far more questions than it answers, the facts overwhelmingly rule out this scenario. 

Yet it's taught to kids as Scientific Truth.  Nevermind it doesn't add up -- it's Science.  Of course, history is full of these kinds of theories.

The right answer to the question will be far more interesting and richer than this yee=hah cosmic car-crash, but probably won't sell as many magazines.  Let's say it will be more interesting to those of us who are thrilled by the way the world works, rather than how good she blowed up.

KENNETH LANE
KENNETH LANE

Just makes me want to say "Daaaaaaaaaaaaaaaaaaaaaaaaaaaa". Why are most studies moronic at best?

Phil Ramsay
Phil Ramsay

Long considered the best theory of how the Earth and Moon came to be - now significant evidence to support that theory,  


Science in action.

Stephen Zhang
Stephen Zhang

l heard about some knowledge that at billions of years there are two planets surrounding the sun in the orbit that earth  in today.Can I imagine that the twins earths collided at a time and then the moon come out?

Mohamamd Akmal
Mohamamd Akmal

I am really new comer, in this field, and hopeful enjoy this debate, what had been happening in nature. More you learn more you know how much you don,t know. There is no doubt in the fact that National Geographic Society in contributing is doing great job to bring the people and nature closer.. 

rob estes
rob estes

Wrong- As a result of such a collision much higher amounts of the other body would be found on both Earth and the moon.  The Earth and moon have been bombarded by essentially the same foreign matter of all types for billions of years due to their relative proximity making me think you guys believe all those moon craters are formed by pimples.

Dwayne LaGrou
Dwayne LaGrou

It makes perfect sense! They said that there was an isotope of oxygen that was not the same as Earths. Then they said that the composition of the moon rocks was the same as the Earth's except for the 12 parts per million. So the other planet had the isotope of oxygen and the Earth's did not but the moon rocks had BOTH, Therefore the moon was a combonition of Earth and Theia material. I don't understand what the confusion is all about. It's cool how we can now use new technology to help answer old questions. Keep up the good work Nat Geo.

I love this stuff.

Kris Warsaw
Kris Warsaw

I'm pretty sure that this theory actually hardly makes sense. For one what are the odds that not only is a massive chunk of space the size of the moon accelerating fast enough after a direct collision with earth that it will leave earths atmosphere just far enough to still be in the gravitational pull? Then that same space chunk to also be almost perfectly spherical, and lastly to have the perfect centripetal force after this collision to be able to actually stay within earths atmosphere and be able to orbit the earth. 


I suppose it was a good idea but there are way too many outrageous factors to conclude that a planetary crater that hit the earth also managed to create the moon. It sounds like nonsense. Maybe that's just my opinion but it just doesn't make sense

Tom Russell
Tom Russell

Yet another nail in the coffin of young planet theorists.

Bobby Salomons
Bobby Salomons

@Paul Vc  I think Raj(esh) Koothrappali would be a better pick as an astrophysicist. :)

James Donnaught
James Donnaught

@Steve White "The facts overwhelmingly rule out this scenario."  I don't suppose you'd care to provide these "overwhelming" facts?

Colin Farrell
Colin Farrell

It's a hypothesis. How can you say that it isn't scientific, though? They explain their procedure and reasoning in the article, and it seems scientific to me. 

Dan Haggerty
Dan Haggerty

@Steve White Their theory made the journal Science. Where did you publish yours? Id be interested to read it.

craig hill
craig hill

@Stephen Zhang Not precisely the same orbit, what are the odds of that? With the Hubble we've never recorded two planets in a single orbit anywhere out there. What's more likely is two planets in the early solar system, Gaia and Theia, were in two different orbits that overlapped, and one day met. 

Don Schneider
Don Schneider

@rob estes , we are so fortunate to have one as informed as you at our disposal. The fact that you were an eye witness to the formation of our moon is so very fortunate for us all. Please continue

craig hill
craig hill

@rob estes The reason, Rob, materiel on the Moon is so readily identifiable whereas on the Earth it's not, is the Moon has no seasons, erosion, weather, volcanoes or earthquakes at all which keep roiling the surface, plunging all that once was well below us, or scattering it to dust elsewhere down thru the billions of years we've been circling the sun. It's there. It's just not readily found. The Moon has been plastered by many more objects in space than the Earth has, because the Moon lacks the Earth's atmosphere to burn most of it up. Even still, the Moon has much more of the original surface than the Earth does. That's what life on Earth does, Rob, it keeps changing its face.  


And a pimple, Rob, would be more like a volcano than a crater. A crater would be more like a pock mark if a volcano were to anthropomorphically age past puberty.

James Donnaught
James Donnaught

@Kris Warsaw  The physics are relatively easy to model, if you've got a powerful enough computer.  There's absolutely no problem getting a large moon in the observed orbit.  The hard part has been explaining the chemistry.  Most models predicted different compositions for the Earth and Moon, but nobody could find those differences, until now.

Here's a video from about a year ago, where the "same chemistry" problem is described as a limitation on the models.

https://www.youtube.com/watch?v=Sp4IEAO_ngU

The newly-discovered oxygen isotope differences allow these models to be refined to fit the facts, rather than being disregarded as inconsistent with the facts.

Scott Brooks
Scott Brooks

@Kris Warsaw I love it when graduates of the universities of Google and Wikipedia try to play physicist.

Suzanne Barnes
Suzanne Barnes

@Kris Warsaw You do understand that this isn't being proposed to have happened within a short period of time, correct?  Astronomical events, even within a solar system, take appropriately astronomical amounts of time to occur-- an impact is abrupt, but accretion and the gravatomical stress through many, many orbits needed to shape debris into a sphere is anything but.  

craig hill
craig hill

@Kris Warsaw The chemical evidence gives it complete sense, Kris, and Pops, whereas your lack of including that evidence denies the sense in you to see it. You wonder what the odds are for two objects in space colliding, and yet that happens pretty much constantly. The reason the smaller thing hit the bigger thing and remained close by is the Theia/Moon is not a super ball, Kris, objects don't bounce off Earth way beyond our gravitational pull. The spherical quality of the Moon is such that any debris circling around the chunk, as you put it, would be abosrbed onto the Moon by the Moon's "gravity", which also always makes the large object in space round. The Moon is where it is because, due to its concentrated bulk and the energy in its orbit, it keeps moving further and further away from Earth. Which means in the beginning the Moon, and the debris that joined it close by, circled very close to the Earth. It wasn't so much in Earth's nascent atmosphere as the evidence of that atmosphere joined it. You posit it makes no sense for this new body to orbit the Earth, yet you give no sensible reason for that fact, unless you're hinting at some supernatural force that just plunked it there, voila?  The problem there is there is zero evidence for that outside your fecund and relatively uninformed imagination, while science has collected evidence that explains it. IOW evidence trumps no evidence or NOTHING would make sense!

Ramiro Fernandez
Ramiro Fernandez

@Kris Warsaw You should probably actually learn the theory before you try to poke holes at it, otherwise you just look silly.


"For one what are the odds that not only is a massive chunk of space the size of the moon accelerating fast enough after a direct collision with earth that it will leave earths atmosphere just far enough to still be in the gravitational pull?"

Pretty good actually, any glancing blow would pretty much guarantee that a large fragment of debris would remain in Earth orbit. Going into orbit is not a precision exercise, any object that is travelling at less than escape velocity will orbit around the Earth. 

"Then that same space chunk to also be almost perfectly spherical"

No one claimed that the space chunk was perfectly spherical after the collision, try actually reading the article! There would have been a huge cloud of debris around the Earth, which Gravity would pull together and would eventually coalesce into a spherical shape - the Moon. 

"and lastly to have the perfect centripetal force after this collision to be able to actually stay within earths atmosphere and be able to orbit the earth."

Ummmm... It didn't stay within Earth's atmosphere, that is a ridiculous claim that no one made. And as I mentioned above, there's no "perfect centripetal force" required to orbit the Earth. Orbits are the natural state of two objects in space - they are either slower than escape velocity and will orbit, or faster than escape velocity and will separate. If the velocity is much too slow, then the orbit of one body will intersect with the other body, and that would be a crash.


So in other words, there are no problems with this theory, there are only problems with your understanding of physics.

Pops Hops
Pops Hops

@Kris Warsaw  Your post makes complete sense. And I was wondering how we know what Theia is really made of. We don't have any data collected from this planet.

James Donnaught
James Donnaught

@Tom Russell  You'll get the all-purpose non-answer:  God put the oxygen isotopes there to make the universe look old.  Every one of the thousands of facts that prove them wrong, and every new fact to be uncovered in the future, is merely a test their faith.

Suzanne Barnes
Suzanne Barnes

@Tom Russell By now it's more nails than coffin, but sadly you'll have a tough time ever getting them to admit that.

Dwayne LaGrou
Dwayne LaGrou

Very well put Rob! Like you, I didn't understand what was so complicated about the explanation they wrote. I thought it was a well written and explained in easy to understand words. Like I said, Well put!

Greg Fietz
Greg Fietz

@Ramiro Fernandez @Kris Warsaw  Thanks Ramiro for intelligently answering my questions. Of course its all just theories, but we must respect scientific theories. Hypothisis-Theory-Fact. that's how all the wonderful inventions we use evolved.

anne boad
anne boad

@Pops Hops - like Kris, you really need to read the article carefully to understand exactly what it says, as opposed to what you think it says.


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