Moon was produced by a head-on collision between Earth and a forming planet, say researchers

Posted: February 5, 2016 by oldbrew in moon, solar system dynamics

Whether this is the last word on the origin of the Moon remains to be seen.

The moon was formed by a violent, head-on collision between the early Earth and a “planetary embryo” called Theia approximately 100 million years after the Earth formed, UCLA geochemists and colleagues report.

Scientists had already known about this high-speed crash, which occurred almost 4.5 billion years ago, but many thought the Earth collided with Theia (pronounced THAY-eh) at an angle of 45 degrees or more — a powerful side-swipe. New evidence reported Jan. 29 in the journal Science substantially strengthens the case for a head-on assault.

The researchers analyzed seven rocks brought to the Earth from the moon by the Apollo 12, 15 and 17 missions, as well as six volcanic rocks from the Earth’s mantle — five from Hawaii and one from Arizona. The key to reconstructing the giant impact was a chemical signature revealed in the rocks’ oxygen atoms. (Oxygen makes up 90 percent of rocks’ volume and 50 percent of their weight.)

More than 99.9 percent of Earth’s oxygen is O-16, so called because each atom contains eight protons and eight neutrons. But there also are small quantities of heavier oxygen isotopes: O-17, which have one extra neutron, and O-18, which have two extra neutrons. Earth, Mars and other planetary bodies in our solar system each has a unique ratio of O-17 to O-16 — each one a distinctive “fingerprint.”

In 2014, a team of German scientists reported in Science that the moon also has its own unique ratio of oxygen isotopes, different from Earth’s. The new research finds that is not the case. “We don’t see any difference between the Earth’s and the moon’s oxygen isotopes; they’re indistinguishable,” said Edward Young, lead author of the new study and a UCLA professor of geochemistry and cosmochemistry.

Young’s research team used state-of-the-art technology and techniques to make extraordinarily precise and careful measurements, and verified them with UCLA’s new mass spectrometer. The fact that oxygen in rocks on the Earth and our moon share chemical signatures was very telling, Young said. Had Earth and Theia collided in a glancing side blow, the vast majority of the moon would have been made mainly of Theia, and the Earth and moon should have different oxygen isotopes. A head-on collision, however, likely would have resulted in similar chemical composition of both Earth and the moon.

“Theia was thoroughly mixed into both the Earth and the moon, and evenly dispersed between them,” Young said. “This explains why we don’t see a different signature of Theia in the moon versus the Earth.” Theia, which did not survive the collision (except that it now makes up large parts of Earth and the moon) was growing and probably would have become a planet if the crash had not occurred, Young said.

Young and some other scientists believe the planet was approximately the same size as the Earth; others believe it was smaller, perhaps more similar in size to Mars. Another interesting question is whether the collision with Theia removed any water that the early Earth may have contained. After the collision — perhaps tens of millions of year later — small asteroids likely hit the Earth, including ones that may have been rich in water, Young said. Collisions of growing bodies occurred very frequently back then, he said, although Mars avoided large collisions.

Source: Moon was produced by a head-on collision between Earth and a forming planet: Research reconstructs massive crash, which took place 4.5 billion years ago — ScienceDaily

  1. Thank you very much for your concise posting, which is a subject of great interest since so much of earth as living planet depends upon the tilt of its axis, day length, early tidal effects (possibly causing plate techtonics), tidal fringes of oceans and seas, and so on, due the moon.

    If “the earth” was in a head on collision then its orbital energy would be reduced.

    Has anyone estimated pre-collision orbital radii for proto-Earth or Theia?

  2. oldbrew says:

    The idea that water came from asteroids is a bit questionable IMO. How many of them would be needed to deliver the sort of quantities we see today – millions?

    And where would the asteroid water be coming from?

  3. oldbrew says:

    The idea that Jupiter shields inner planets from comets and the like has taken a knock.

    ‘Not only is the “Jupiter as shield” concept, implying that the planet shields Earth from comet impacts, not true, but perhaps Jupiter’s most important role in fostering the development of life on Earth was just the opposite — delivering the volatile materials from the outer Solar System needed for life to form.’

  4. oldbrew says:

    Another team seems to have said something very similar in 2012.

    ‘Oxygen isotopic compositions have been found to be identical between terrestrial and lunar samples, which is inconsistent with numerical models estimating that more than 40% of the Moon-forming disk material was derived from Theia.’

    These researchers also investigated titanium: ‘we find that the 50Ti/47Ti ratio of the Moon is identical to that of the Earth within about four parts per million’.

    ‘The isotopic homogeneity of this highly refractory element suggests that lunar material was derived from the proto-Earth mantle, an origin that could be explained by efficient impact ejection, by an exchange of material between the Earth’s magma ocean and the proto-lunar disk, or by fission from a rapidly rotating post-impact Earth.’

    Hard to tell from the abstracts what the new research has found that wasn’t reported in 2012.

  5. p.g.sharrow says:

    A near miss with a giant body would accomplish the same feat. Think about the celestial mechanics needed for a head-on collision. I vote no. The Earth / Luna pair points to another conclusion.
    Oldbrew’s concept of Saturn / Jupiter pulling outer materials into the inner system sounds logical to me. All that is required is to slow the outer orbiters speed to have them “fall”

  6. jim says:

    This is the scientific training for today. They are 100% certain based on several isotope tests? Basically three samples of the moon, and five from earth? Can tell the overall composition? And whatever? No wonder science is getting a black eye. Assured from the obvious contamination issues, age and accumulation issues, custody issues, what is their to show the one set of samples were from the moon, after all some of the gifts proved to be fake. And some tests done recently, believe I would rather trust the immediately done sample from way back when they first landed. Less contaminations. Makes one wonder?

  7. oldbrew says:

    ‘In 2014, a team of German scientists reported in Science that the moon also has its own unique ratio of oxygen isotopes, different from Earth’s. The new research finds that is not the case.’

    So what did the German scientists do wrong, or fail to do?

  8. oldmanK says:

    oldbrew said “And where would the asteroid water be coming from?”

    Water is H2O. Has the oxygen in the water a different isotope ratio, if its source is asteroids?

  9. oldbrew says:

    oldmanK: this looks relevant.

    ‘The Rosetta spacecraft has detected water coming off comet 67P, the rubber duck-shaped lump of ice and dust that it placed the Philae robotic lander on last month.

    The presence of water is not a surprise, but what has wrong-footed researchers is the make-up of the water, which is nothing like that seen on Earth.

    Measurements from Rosetta’s Rosina instrument found that water on comet 67P /Churyumov-Gerasimenko contains about three times more deuterium – a heavy form of hydrogen – than water on Earth.’

    Baffled scientist time again 😉

  10. oldbrew says:

    Richard H asked: ‘Has anyone estimated pre-collision orbital radii for proto-Earth or Theia?’

    Not that I know of, but to collide it would seem that one or other had a very elliptical orbit path that crossed the other one. Unless someone can offer another scenario…

  11. catweazle666 says:


    I recollect there was an essentially identical article in Scientific American around 35 years ago asserting that the Moon was the result of a collision between the Earth and a Mars sized planetoid, with evidence from analyses of the moon rocks brought back by the Lunar expeditions.

  12. Graeme No.3 says:


    Failure to give way at the intersection?

  13. Why did the sperm cross the road?

  14. hunter says:

    Imagine just how upset the climate obsessed of proto-Earth must have been to see the oceans boiling away, the crust melting and a considerable fraction spinning away to form the moon.
    Now THAT would be catastrophic climate change…..

  15. oldbrew says:

    Hunter: catastrophic, but here we are talking about it 😉

    Climate models say we’re doomed to unlimited disasters by a few molecules of a trace gas unless…blah blah.

  16. E.M.Smith says:

    I see others covered most of the points I noticed. Sample size, distribution, orbital mechanics problems, etc. I’ll just add: A head-on requires a retrograde Theia, but then the moon will not form close to Earth as the mass gets strung out too far away and with too much delta V between the Earth and moon parts.

    Then there is the ASSUMPTION that Theia must have formed from different source material, yet it might well have formed from the same band of material as the Proto-Earth, being formed in the same general band, then having the glancing blow that forms the moon. This is rather like Ceres and Vesta in the asteroid belt. One day they may collide as all the orbital perturbation and nearby junk jiggles around, yet clearly are formed of the same source stuff. We have an existance proof of multiple body formation in one band, but no existance proof of retrograde planet orbits…

    Finally, WHY do other planets have different isotope ratios? Might it be due to distance from the Sun, and 4.5 billion years of solar radiation? If so, then the Earth Moon system ought to have matching ratios.

    As noted by others, this looks like junk science desperate to publish something, anything…

  17. p.g.sharrow says:

    Our various discussions of atomic processes and Solar radiations would seem to me an indication, that the local isotopic distribution is a creature of local atomic process and not a result of original creation distribution. We now know that placement in the Suns gravity well has an effect on the speed of atomic processes. Radiation intensity is also a factor of distance from the solar furnace. So after 4.5 billion years of exposure to similar conditions, the Earth-Luna isotopic signature would be very much appear to be the same while, celestial objects that have existed under different conditions exhibit different isotopic signatures…pg

  18. p.g.sharrow says:

    Richard heath says:
    February 6, 2016 at 11:40 am

    Why did the sperm cross the road?
    To get to the ovum side. ;-)pg

  19. Power Grab says:

    @ Hunter: That’s what I was thinking. Else why would there be the tidally-locked thing going on between Earth and Luna?

  20. oldbrew says:

    Nearly all moons have synchronous orbits where one rotation = one orbit of its planetary owner aka tidal locking.

  21. Wayne Job says:

    I would tend to believe the history of the Earth from the legends of Sumer. They say a large watery planet gave our Earth a glancing blow carving a big hole in the Earth and dumping huge quantities of water . I cannot remember what they said about the moon but I would prefer to believe their version.
    Modern scientists seem to be headline seekers, rather than seekers of truth.

  22. I would like to see the reference to this Sumerian myth. The contemporary problem with such traditional information being factual is that there had to be an observer that existed before humanity or indeed life itself, with whom there was subsequent intellectual contact. Or one would have to be able to deduce the facts of it, as science is attempting today.

  23. Chaeremon says:

    Re: … Sumer. They say a large watery planet gave our Earth a glancing blow … and … huge quantities of water

    For earthshine the oceans must reflect light (they also preserve heat),

    The rest is literary invention for dissemination of freaking unknowingness /sarc

  24. oldmanK says:

    Chaeremon says “The rest is literary invention for dissemination of freaking unknowingness /sarc”

    That depends much on interpretation, and to a good extent on bias (and agenda). If you are looking for fairies and goblins and such like, then it is likely invention. If you are trying to interpret what is sometimes right under our noses than it might be a very different matter.

  25. Chaeremon says:

    @oldmanK Re: That depends

    The N-Body problem looks horrible, even when virtually solved academically,


  26. oldmanK says:

    Chaeremon, there was a time or era for these —speculations?? That was a dark age.

    I would put the sumerian myth in another category.

  27. tallbloke says:
    Zecharia Sitchin Translation: As a Cosmology of the Solar System with the names of the gods as the Sumerian names of our 9 planets, with Tiamat (as old Earth), a 10th planet called Nibir (Marduk), our Sun, and Earths moon (Kingu). An intruder planet called Nibiru, enters the early Solar System making Uranus turn a 90 degree axis, pulled a moon of Saturn away becoming Pluto, then has a moon impact with Tiamat (old Earth) between Mars and Jupiter. Half of Tiamat becomes the Asteroid belt and Comets. The other half of Tiamat from a second impact is pushed to 3rd from the sun as new Earth keeping Tiamats old Moon (Kingu). Marduk now as Nibir is locked in a counter clockwise 3600 year orbit. From Sitchin’s — The Lost Book Of Enki. This translation is an example of a work of pseudo-religion, and Sitchin himself is accused of not being a qualified language scholar.[9]