When worlds collide – study says our moon was formed by a collision with planet-sized body

Artist’s depiction of a collision between two planetary bodies. Such an impact between the Earth and a Mars-sized object likely formed the Moon.

From the European Association of Geochemistry

New isotopic evidence supporting moon formation via Earth collision with planet-sized body

A new series of measurements of oxygen isotopes provides increasing evidence that the Moon formed from the collision of the Earth with another large, planet-sized astronomical body, around 4.5 billion years ago. This work will be published in Science* on 6th June, and will be presented to the Goldschmidt geochemistry conference in California on 11th June.

Most planetary scientists believe that the Moon formed from an impact between the Earth and a planet-sized body, which has been given the name Theia. Efforts to confirm that the impact had taken place had centred on measuring the ratios between the isotopes of oxygen, titanium, silicon and others. These ratios are known to vary throughout the solar system, but their close similarity between Earth and Moon conflicted with theoretical models of the collision that indicated that the Moon would form mostly from Theia, and thus would be expected to be compositionally different from the Earth.

Now a group of German researchers, led by Dr. Daniel Herwartz, have used more refined techniques to compare the ratios of 17O/16O in lunar samples, with those from Earth. The team initially used lunar samples which had arrived on Earth via meteorites, but as these samples had exchanged their isotopes with water from Earth, fresher samples were sought. These were provided by NASA from the Apollo 11, 12 and 16 missions; they were found to contain significantly higher levels of 17O/16O than their Earthly counterparts.

Dr Herwartz said “The differences are small and difficult to detect, but they are there. This means two things; firstly we can now be reasonably sure that the Giant collision took place. Secondly, it gives us an idea of the geochemistry of Theia. Theia seems to have been similar to what we call E-type chondrites**.If this is true, we can now predict the geochemical and isotopic composition of the Moon, because the present Moon is a mixture of Theia and the early Earth. The next goal is to find out how much material of Theia is in the Moon”.

Most models estimate that the Moon it is composed of around 70% to 90% material from Theia, with the remaining 10% to 30% coming from the early Earth. However, some models argue for as little as 8% Theia in the Moon. Dr Herwartz said that the new data indicate that a 50:50 mixture seems possible, but this needs to be confirmed.

The team used an advanced sample preparation technique before measuring the samples via stable isotope ratio mass spectrometry, which showed a 12 parts per million (± 3 ppm) difference in 17O/16O ratio between Earth and Moon.

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Dr Daniel Herwartz will present “The elevated Δ17O composition of the Moon relative to the Earth” to the Goldschmidt conference, Sacramento, California, on 11th June at 09.45, Eastern Time. The Goldschmidt conference is the world’s leading annual conference on geochemistry, http://goldschmidt.info/2014/

Please mention this Goldschmidt presentation in any story which results from this press release.

Conference Abstract

The elevated Δ17O composition of the Moon relative to the Earth

D. HERWARTZ, A. PACK, B. FRIEDRICHS AND A. BISCHOFF

We present the first isotopic evidence for giant impactor material in lunar rocks. The Moon presumably formed from the debris of a giant collision between two proto-planets (‘giant impact hypothesis’). Most numerical models of the collision predict that the Moon dominantly formed from impactor material. Thus, the Moon should inherit the isotopic composition of the impactor. So far, however, no isotopic difference between the Earth and the Moon has been resolved. We have measured the triple oxygen isotopic composition of APOLLO basalts using an improved protocol [1]. We show that the Δ17O isotopic compositions of lunar APOLLO basalts is elevated by 12 ± 3 ppm relative to the Earth. We also show that enstatite chondrites (EC) comprise an even higher Δ17O of 51 ± 6 ppm relative to the Earth. Thus, EC cannot be the sole building blocks of the Earth. Instead EC may resemble the composition of the giant impactor. If so, the Moon may be composed of ~40% impactor material, consistent with recent numerical models of the collision [2,3]. In an alternative scenario the lower Δ17O composition of the Earth could reflect a late veneer with low Δ17O. Addition of 0.5% carbonaceous chondrites would be sufficient to lower the Δ17O of silicate Earth by 12 ppm.

Additional Notes

*The paper on which this presentation is based will be published in Science on 6th June 2014 (details below). The full paper will be available after the embargo at: http://www.sciencemag.org/lookup/doi/10.1126/science.1251117

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53 thoughts on “When worlds collide – study says our moon was formed by a collision with planet-sized body

  1. “The next goal is to find out how much material of Theia is in the Moon”.
    Big question. Why? Who cares? Sounds like a makework task from the Great Depression’s New Deal program.

  2. arthur4563 says:
    June 5, 2014 at 12:06 pm

    IMO most of Theia is on earth, or in it, if the hypothesis be valid.

    The impact hypothesis has been the best supported explanation for moon formation for about 40 years.

    The latest wrinkle is that slow-motion collision with a second moon formed the highlands on the dark side.

  3. “Most models estimate that the Moon it is composed of around 70% to 90% material from Theia, with the remaining 10% to 30% coming from the early Earth. However, some models argue for as little as 8% Theia in the Moon. Dr Herwartz said that the new data indicate that a 50:50 mixture seems possible, but this needs to be confirmed.”

    Why do I have an ugly feeling that this “research” is done on some computer modeling concept where you write the program with your belief set in place and lo and behold, the program output is “proof” that it happened?

    “Dr Herwartz said “The differences are small and difficult to detect, but they are there. This means two things; firstly we can now be reasonably sure that the Giant collision took place. Secondly, it gives us an idea of the geochemistry of Theia.” Ah, but the are “significant” differences, even though they are small and hard to detect. And we are probably talking proxies, by the way, again being treated as if they are absolutes.

    Looks like more than just climate science has lost its way.

  4. … and Mars was in collision with a large body, sometime long ago, losing mass and atmosphere. Could Mars have been Theia?

  5. This doesn’t seem like news to me… it’s long been accepted that the Moon was formed by a mega-collision. Is there something new here?

  6. Is this a follow up on something I read about several decades ago or is the study completly recycled …?

  7. This is not a new theory. In fact it is the most widely accepted one for lunar formation, based on lunar rock analysis ( little heavy mantel basalt, lots of light crustal silicate) and orbital spin (we never see the back side of the moon from Earth. There must be a reason.)
    What is new is the additional confirming isotope analysis.
    The hype here is equivalent to the 2014 paper rediscovering what Darwin knew in 1834, that coral atolls grow and decline with sea level, as corals are alive!

    It seems most scientific papers now come with attached obligatory hype. Still, interesting for those who did not know how the moon was made. Watt else is up with astrophysics? Gravity wave polarization of the CMBT, simultaneously validating Einstein’s general relativity AND the Big Bang/ Inflation. Nobels forthcoming after second validation by a European satellite end of this year.

    Note the science thingy. A second validation of an observation which itself only confirms theories already tested otherwise (black holes for general relativity,the mere existence of the CMBT for Bang/inflation). Now in climate science, we have missing heat where the laws of thermodynamics say it cannot go, and a darned pause that should not be, and polar bears thriving instead of dying. Some sort of a climate science thingy/ reality disconnect. Must be a Matrix sort of reality, because the climate computer models cannot be wrong… Right, Morpheus? All topical essays in my somewhen (soon?) next book.

  8. sophocles says:
    June 5, 2014 at 12:19 pm

    No. All large bodies in the solar system have sustained collisions.

    Mars took a hit about 4 BA, but its impact wasn’t the same one which formed earth’s moon, hypothetically. This conclusion is based upon modeling, but of a higher order than GIGO, worse than worthless, repeatedly falsified GCMs based on unwarranted assumptions:

    http://www.universetoday.com/15262/two-faces-of-mars-explained/

  9. Might that planet sized body have been named Alice?
    Oh wait. This was about how it was formed.
    Never mind.

  10. Hasn’t that been the theory all along?
    I really want to know when Tyson DeGrasse is going to edited that Cosmos episode.

  11. So maybe Veliskovsky was not so much a nut case after all, who would have thunk it!(Galileo was one as well).

  12. If it happened then, it can happen again. We should apply the precautionary principle and start dealing with it now. Otherwise we’re doomed.

  13. jmorpuss says:
    June 5, 2014 at 3:13 pm

    Not exactly, but so much crust missing up there in orbit helps account for plate tectonics.

    Here’s a NASA animation of the two-moon hypothesis to which I alluded above:

  14. Did this event give Earth it’s water, as the moon gave up all it’s ice as water vapor on impact?

  15. jmorpuss says:
    June 5, 2014 at 4:21 pm

    Earth’s water mostly comes from comets, although chemical processes here also produced some, largely lost during impact events.

  16. For the two moon theory to stand up your saying Earth has always had its strong electromagnetic properties that would hold these moons in place. I’m not shaw this is correct ,it’s my belief that impact created Earths strong. Electromagnetic field lines so Earth was capable of holding a saterlite of the size of the moon . If you strike a iron bar hard enough you will create magnatism . Until Earth was impacted it was as lifeless as Venus and Mars because Earth also had weak magnetic properties incapable of holding on to a atmosphere let alone a moon. Just my thoughts

  17. Way back then… was, CO2 through some unknown mechanism, the cause of the collision?
    If current models are backcast far enough what do(-oes) the “data” show?

  18. Velikovsky pushed a version of this idea in the 40s and 50s.

    http://en.wikipedia.org/wiki/Worlds_in_Collision

    “In Cosmos, Sagan also criticizes the scientific community for their attitude toward Velikovsky, stating that while science is a process in which all ideas are subject to a process of extensive scrutiny before any idea can be accepted as fact, the attempt by some scientists to suppress outright Velikovsky’s ideas was “the worst aspect of the Velikovsky affair.”

    I was present at one of these debates and found the vitriol towards an unpopular idea surprising. Interesting to see it again these times toward skeptics.

  19. So does the moon have usable ores after all?
    10 to 50% composed of earth material? What kind?
    What other evidence supports or contradicts this supposition?

  20. ” ( little heavy mantel basalt, lots of light crustal silicate)”

    I’m wondering how much silicate had been fractionated 4.5 bya.

  21. @Jmorpuss, Look at the Bering sea it has the same or similar (“meteor” print like the Gulf of Mexico, Google it as does Eastern Canada ). If there still people that do not realize the Earth was bombarded at the same time as the moon i wonder what evidence they can present. I am also wondering about the “Billions and Billions” of years statement by so many scientists. I still wonder what we would have looked like if WE were hit by the comets that hit Jupiter a few years ago (nine in a row if I am correct), I do not think there would have been much of a diary afterwards, call me a skeptic I guess.

  22. jmorpuss says:
    June 5, 2014 at 4:56 pm

    It sounds as if you have electromagnetism confused with gravitation.

  23. asybot says:
    June 5, 2014 at 9:55 pm

    Earth was hit repeatedly during the bombardment eras, & less frequently since. Craters are visible here, but often worked over by earth’s active geology so that they’re not as obvious as on the moon or Mars.

    That said, the Bering Sea & Gulf of Mexico probably arose from volcanic & tectonic forces rather than impacts. A Canadian geologist did however propose the Gulf as a crater responsible for the Permian mass extinction event, but his hypothesis hasn’t garnered support.

  24. So, the damage to our planet was actually caused by some idiot crashing their “planet-sized body” into it before we got it. Can’t we make an insurance claim?

  25. This is an interesting article. I have questions (not criticisms), looking for clues:
    1. Earth is said to be 4.5bn years old. Isn’t a collision at exactly that time to form the moon a bit of a coincidence, ie. unlikely?
    2. The moon rotates exactly in phase with Earth’s rotation. Isn’t that very unlikely if it was chipped off by impact? [I say "chipped" but maybe Earth was liquid then, and thus the moon too?]. The key word is “exactly”.
    3. How were other planets’ moons formed? Do they also rotate exactly in phase with their planet’s rotation?
    4. How were the sun’s moons (ie. planets) formed? Do any of them rotate exactly in phase with the sun’s rotation?

  26. “Mike Jonas says:
    June 5, 2014 at 11:35 pm

    1. Earth is said to be 4.5bn years old. Isn’t a collision at exactly that time to form the moon a bit of a coincidence, ie. unlikely?
    It’s no coincidence. With two or more bodies in the same orbital plane and roughly the same distance from the sun, sooner or later they’re going to collide.
    The planets all formed by accretion of smaller bodies in their orbits. The forming of the moon when a Mars size planetoid hit earth was one of the last major collisions in earth’s formation.
    2. The moon rotates exactly in phase with Earth’s rotation. Isn’t that very unlikely if it was chipped off by impact? [I say "chipped" but maybe Earth was liquid then, and thus the moon too?]. The key word is “exactly”.
    No, the moon may have been rotating faster in the past. With tidal friction, the moon slowed down until it now shows only one face to earth. The earth is ALSO slowing down over the aeons. During the Jurassic- with Allosaurs and Stegosaurs, there were about 380 or 390 days in the year due to earth’s faster rotation. Given enough time, the earth wil also ultimately show only 1 face to the moon

  27. jmorpuss says:
    June 5, 2014 at 4:21 pm

    Did this event give Earth it’s water, as the moon gave up all it’s ice as water vapor on impact?

    No, most of our water (and atmosphere) came here during the late great bombardment. But the collision did blow into space our early heavy atmosphere allowing us to escape, unlike Venus, a runaway green house atmosphere. Also Earth has a larger then expected iron core. I suspect Theia donated her core to the young Earth too. Life on Earth would not be possible without Theia. Theia is the mother of life on this planet.

  28. we never see the back side of the moon from Earth. There must be a reason.
    ===============
    spin stabilization between the planets and moons is common throughout the solar system. For example, the rotation of Venus is synchronized to the orbit of Earth, such that Venus always shows the same face to earth at closest approach.

    The problem for science is that the tidal forces involved are thought to be too small to cause this synchronization. Yet it is common, as is the near integer resonance between the orbital periods of the planets and moons. We cannot explain it, yet it is there.

  29. the moon gave up all it’s ice as water vapor
    ==============
    water exists on the earth’s surface because the earth has a hot core. The steam pressure at the boundary layer between liquid and boiling water within the earth’s mantle prevents the water from draining towards the center of the earth.

  30. Venus, a runaway green house atmosphere
    ===============
    Venus surface temperatures correlate much better with 90 atmosphere of pressure than they do with CO2 concentrations. Rather, the very low difference in daytime and nighttime temperatures on Venus, in spite of its very slow rotation, are explained by high CO2.

  31. Something most people don’t realize about our Moon:

    There is a final, even more bizarre twist. Because of Moon-induced tides, the Moon is gradually receding from Earth at 3.82 centimeters per year. In ten million years will seem noticeably smaller. At the same time, the Sun’s apparent girth has been swelling by six centimeters per year for ages, as is normal in stellar evolution. These two processes, working together, should end total solar eclipses in about 250 million years, a mere 5 percent of the age of the Earth. This relatively small window of opportunity also happens to coincide with the existence of intelligent life. Put another way, the most habitable place in the Solar System yields the best view of solar eclipses just when observers can best appreciate them.- “The Privileged Planet”

  32. If the two moons theory were correct, shouldn’t the moon have SOME rotation other than that of it’s monthly Earth-centric rotation? What would be the odds on a large collision that wouldn’t impart some spin? Or alternatively, could Earth’s gravity and tidal forces cancel over time any nascent rotation caused by a large collision?

  33. “Mickey Reno says:
    June 6, 2014 at 7:11 am
    If the two moons theory were correct, shouldn’t the moon have SOME rotation other than that of it’s monthly Earth-centric rotation? ”

    It probably DID have some rotation earlier. With tidal friction, the moon’s rotation has slowed down so that it now has only one side towards earth. The earth’s rotation is ALSO slowing down, but since the earth has about 81 times as much mass as the moon, the rate of slowing is much smaller.

    As Joe G. pointed out, as earth’s rotation slows down, thanks to that tidal friction, the moon gradually recedes from earth to conserve angular momentum in the earth-moon system. If the sun doesn’t swell up enough to fry the earth first, ultimately earth’s rotation will continue to slow down until only one side always faces the moon.

  34. At 4.5 biliion years ago everything was collision- and accretion, because this was when our solar system was being formed. so, what’s the news?

  35. “Most models estimate that the Moon it is composed of around 70% to 90% material from Theia, with the remaining 10% to 30% coming from the early Earth. However, some models argue for as little as 8% Theia in the Moon. Dr Herwartz said that the new data indicate that a 50:50 mixture seems possible, but this needs to be confirmed.”

    So according to the models the moon is either 10,30,50 or 92% Earth based matter.
    aka: no friggin idea !

    Sounds like a close parallel to the amount of 20th c. warming that is human caused.

  36. So, you can be “reasonably certain” that a giant impact took place just by measuring a miniscule difference in isotope concentrations? I am not buying this at all.

    By the way, have any of the artists creating these artists’ representations of giant impacts ever heard of a Roche limit?

  37. In reply to Dasein:
    Stricktly speaking, the Roche limit only applies to big dust balls. In reality, there is some force ( I guess electrical) holding rocks , and you and I, together more firmly than a big ball of dust, so it takes more force to pull an object apart than that given by the Roche limit.

  38. OK! Tidal forces transfer energy from the earth to the moon, resulting in the moon reaching a higher orbit (3.82cm further) each year. Let’s back this up. As we go back in time, the tidal forces get larger and the moon’s orbit change is greater each year. Somewhere about one and a half billion years ago the moon would be close enough, and the tidal forces large enough, to completely destroy, or deform, the surface of the earth. Geologists tell us this did not happen.

    Question: Where was the moon during the first 3+ billion years of its existence?

  39. I don’t show you my backside either. Seems odd that showing one’s backside is called “mooning” when the moon itself is polite enough not to.

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