How did the Moon form? Giant impact theory questioned

Posted: January 9, 2017 by oldbrew in moon, solar system dynamics
Tags: ,

Take that [credit:]

Take that [credit:]

It seems that there’s always another Moon theory, or variation of an existing one, in the pipeline and here’s one of the newest contenders. Each seems to have its own issues though.

The most widely accepted theory about how the Moon formed has been challenged, with scientists saying a series of large impacts – rather than one giant collision – created our natural satellite, reports the IB Times.

By running numerical simulations, researchers say the Earth being hit by several large planetary bodies would help explain why our planet and the Moon are largely composed of the same material – a problem that has plagued scientists for decades.

The giant impact Moon formation theory was first proposed in the mid-1970s. It says a Mars-sized protoplanet called Theia smashed into Earth around 4.5 billion years ago. The ejected material created a disk of debris, molten rock and gas that eventually condensed to form the Moon.

However, there is a big problem with this theory. If it was correct, the Moon’s composition should be a mix of both Earth and Theia. For this to happen, Theia would have had to be almost identical to Earth in terms of its composition, which is highly unlikely.

A team of scientists from Israel has now come up with a potential solution. In a study published in Nature, they carried out almost 1,000 simulations of large – but not giant – planetary bodies impacting Earth. Their findings showed a series of big impacts could explain the Moon.
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IB Times report continues here
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Last part of report:

However, the theory also comes with its own problems, he added. “Rufu et al. envision a scenario where following each impact, a new moonlet forms from the disk, migrates outwards and merges with the growing Moon,” he said. “Although they do not model the Moon’s accretion, their analysis suggests about 20 impacts are required to build the Moon — assuming perfect merging of every moonlet. If, as seems likely, merging is imperfect or some moonlets are lost, many more impacts may be required, thus making the necessary sequence of events far less probable than any of the more exotic single-impact scenarios.”

Concluding, he added: “For final adjudication, we must now look for firmer evidence on each side.”

  1. oldbrew says:

    DT version of the story has more graphics etc.

    Moon formed from merger of 20 little ‘moonlets’, new theory suggests

  2. jim says:

    More accretion?, bodes less well for a sustainable habitat. That would make mining less appealing, no lodes to develop.

  3. It is mush. I have communicated the obvious, and true, reason for Earth’s too-huge (that’s a clue too) moon, giving the very simplest evidence:

    “The Clockwork Moon Science Ignores”

  4. Bitter&twisted says:

    “Clockwork Moon”? Oh dear!

  5. richard verney says:


    It is only by chance that those alive today see a perfect eclipse. In its early development the Moon was much nearer the Earth, and it is gradually receding. In tens of millions of years, it will not give rise to a perfect eclipse.

    When the moon was close to the Earth, the Earth day was only around 4 to 7 hours, it is now 24 hours as the Moon has recedes. As the moon further recedes, the Earth day is getting longer heading to 25 hours and beyond. On a cosmic scale, it will not be that long before there are 48 hours in an Earth day.

    One should not read too much into what is obviously just coincidence, may be a happy coincidence for us, but mere coincidence none the less.

    There is more in your Venus warming theory.

  6. p.g.sharrow says:

    I find this investigation adds very little to the argument as to creation of the Earth / Luna pair. Far too many moving parts in their assumptions of cause and effect to realistically yield the present known result.

    I lean toward a non collision of a very near pass from a very large interloper from behind to better explain present known conditions…pg

  7. oldbrew says:

    In the Pluto-Charon binary system (same rotation period for both) the two bodies have similar densities. But the Moon’s density is only 60% that of Earth.

    If The Moon is debris from Earth, why is its density so different? Another tricky one for theorists. One argument might be that the core is the densest part of Earth, and it was some (less dense) outer parts that broke off in the alleged collision.

    The Moon has a very weak magnetic field.

  8. linneamogren says:

    The best theory as to why the density of Earth and the moon are very different is due to what material was thrusted into space. If impact occurred ( most likely only once regardless of this new hypothesis ) then most of the debris would be the Earths upper mantle rather than its inner core. This explains why the moon does not have the density of Earth yet still be made from its material.

  9. linneamogren says:

    Oldbrew beat me to the punch lol

  10. oldbrew says:

    A hybrid theory might be that a primary collision flung debris into space, some of which was then hit by other bodies or debris already in circulation. The Moon’s surface composition is similar to that of Earth, but inside things must be different e.g. hardly any magnetism.

  11. linneamogren says:

    NASA has recently gone over Apollo data and they have come to agreement that the moon has a very similar core to ours. Soon NASA will have more advanced probes for the moons inner structures and material.

  12. oldbrew says:

    Whatever happened to form the Moon, it was a very long time ago it seems.

    Scientists: Moon Over the Hill at 4.51 Billion Years Old
    CAPE CANAVERAL, Fla. — Jan 11, 2017, 3:42 PM ET

  13. oldbrew says:

    NASA just explained why Moon dust is ‘levitating’ above the lunar surface
    Bec Crew, ScienceAlert
    Jan. 10, 2017, 8:45 PM

    “This new … model resolved a fundamental mechanism of dust charging and transport, which has been puzzling scientists for decades,” said one of the team, Xu Wang, from NASA’s Ames Research Centre in California.
    . . .
    “We expect dust particles to mobilise and transport electrostatically over the entire lunar surface, as well as the surface of any other airless planetary body,” said Wang.