The Latest and Most Scientific Theory of Our Moon's Origin

(Not an Episode of The Sopranos

Giant-impact Hypothesis

                     Wham! Bam! Thank You, Ma'am!


The urge to explain and understand the world of natural phenomena cannot properly be seen as particularly scientific, but must be seen, rather, as generally human. It is well known that long before Copernicus described his radical and revolutionary picture of a helio-centric universe that human beings, from around the world, were giving form to the origins, motions and motives of the vastly complex and depth-less sky above them. Through mythic narratives of super-human heroes and anthropomorphic goddesses and gods, pre-scientific societies placed order among the cosmos.                                    --  NASA Lunar Prospector Site

Aristarchus of Samos, who lived from 310 to 230 BC was an early Greek astronomer who, for his time, amazingly got very close to guess how many earth radii we are from the moon (60, or approximately 230,000 miles, but actually 55-63) using earth's eclipse shadows. He was quite a bit further off with his estimated distance to the sun however. Significantly bearing on scientific truth, he did figure that the moon orbited the earth. Heraclides of Pontus (387-312) used to get that credit, but research has superseded that. All this attribution comes from quotes from later philosopher/astronomers.

We can thank Aristotle, (384-322) Archimedes (287-212 BC - who quotes Aristarchus), Copernicus (1473 - 1543) and Galileo (1564 - 1642) for great strides (and literal sacrifice: these Heliocentric theories were burned and buried like their proponents by the Roman Catholic Church.) in understanding the way the planets and moons spin in the right way in the Great Clockworks in the Heavens.  Descartes was naturally gun-shy after Galileo's trials, and so his capture theory (more detail below), was published in 1664.  He humbly added: "I have not undertaken to explain everything." The moon, which originally was more 'football' shaped, stabilized to its present configuration after billions of years of earth's and its own tidal forces.

To The Moon, Alice (In Wonderland)

Orbits are important regarding the formation of our lunar cousin who gives us that wonderful nightlight, second only to Sol,  during the early infancy (a Fifty million year old one!) of our solar system, there was another semi-molten sphere in an elliptic whose destiny ended by crashing into the earth, burying it into it, and spewing debris out.  These particles and pieces later congealed into what is also called Luna.  The National Aeronautics and Space Administration (NASA) sent the Apollo Space Missions, (the Moon Landing), which, though it brought back rocks, did not hammer a solid theory (according to Hartmann recalling it in 1984) but it did aid with analyzing the samples.  Also providing key information was the probe, Clementine (1994 this lunar orbiter first sensed water), and NASA's Sensing Satellite corroborated it in 2009); and the Discovery Lunar Prospector (1998) are some of the contemporary lunar explorers that continue to debunk earlier theories of our first satellite.  With these sophisticated space instruments, scientists have now calculated the amount of iron in each as too divergent, and  importantly the ratio of mass. Peter Tyson of NOVA points out:

Moon rocks contain few volatile substances (e.g. water), which implies extra baking of the lunar surface relative to that of Earth. The relative abundance of oxygen isotopes on Earth and on the Moon are identical, which suggests that the Earth and Moon formed at the same distance from the Sun.


V. S. Safronov, Soviet Cosmogonist in the late 1950's, was working on the formation of elements of our solar system including the moon; he focused on the satellite swarms of particles, whether they could be massive enough to form a moon.  In 1962, another Russian, E. L. Ruskol published a paper for the SAO (Special Astrophysical Observatory) and  NASA, "The Origin of the Moon."  Later, he and his aforementioned colleague published in 1992 for a Cal Tech conference, "Formation and evolution of planets,"  once again discussing particles coming into a solid. Importantly they wrote:

Small bodies of the Solar System are byproducts of the formation of the planets. The fall of large bodies onto the planets at the last stage of accumulation brought much of stochastics into the process (planetary obliquities, etc.). It led to a much higher initial temperature of the Earth's mantle, early beginning of partial melting and differentiation, which determined its pre-geological evolution.
A few scientists in the 1970's became enlightened at Harvard University and the Planetary Science Institute, with William Ward, Don Davis and Alistair Cameron.  They did some rethinking of a former problem that had thought the solar system had run out of planet sized meteors.  Their idea of a planet sized impact while the earth was still soft accounted for the extra mantle on the earth, and the unique alignments (we have a 23.5 degree tilt) we enjoy with tides (the moon's angular momentum) and more. University of Denver and Southwest Research Institute in Boulder, Robin M. Canup, who was inspired from a 1984 Koni, Hawaii Conference, made improvements on the earlier ideas with computer simulations first published in 1997's  Nature, recreating that collision 4.5 billion years ago called The Big Whack. (They estimate the birth of the Solar System at 4.6 billion).  She postulated about earth's composition and its relation to the moon's:
However in general, as the amount of material which must be added to the Earth after the Moon-forming impact in a given impact scenario increases, difficulties with the Moon becoming compositionally more similar to the Earth and the other terrestrial planets also increase.

Canup's ad hoc additional idea to the impact theory was dubbed the Big Whack II, she proposed that the earth was hit against the spin by a second sphere slowing the rotation.  (This cohesion of debris, which is where Cameron left off, she questioned at first, then by the end of 1997 she was convinced, and the cosmic event took only a year!.)   Edward Belbruno and Richard Gott of Princeton University concur with this concept. Where are the remains for proof, one might ask;  Two thirds dissipated into the atmosphere, after the third heavy part went in earth's mantle. Her final abstract on this is as follows:

We present results of about 100 hydrodynamic simulations of potential Moon-forming impacts, focusing on the “late impact” scenario in which the lunar forming impact occurs near the very end of Earth’s accretion (Canup & Asphaug 2001). A new equation of state is utilized that includes a treatment of molecular vapor (“M-ANEOS”; Melosh 2000). We assess the sensitivity of impact outcome to collision conditions, in particular how the mass, angular momentum, composition and origin (target vs. impactor) of the material placed into circumterrestrial orbit vary with impact angle, speed, impactor-to-target mass ratio, and initial thermal state of the colliding objects.
The most favorable conditions for producing a sufficiently massive and iron-depleted protolunar disk involve collisions with an impact angle near 45 degrees and an impactor velocity at infinity < 4 km/sec. For a total mass and angular momentum near to that of the current Earth-Moon system, such impacts typically place about a lunar mass of material into orbits exterior to the Roche limit, with the orbiting material composed of 10 to 30% vapor by mass. In all cases, the vast majority of the orbiting material originates from the impactor, consistent with previous findings. By mapping the end fate (escaping, orbiting, or in the planet) of each particle and the peak temperature it experiences during the impact onto the figure of the initial objects, it is shown that in the most successful collisions, the impactor material that ends up in orbit is that portion of the object that was in general heated the least, having avoided direct collision with the Earth.
Using these and previous results as a guide, a continuous suite of impact conditions intermediate to the “late impact” (Canup & Asphaug 2001) and “early Earth” (Cameron 2000, 2001) scenarios is identified that should also produce iron-poor, ~ lunar-sized satellites and a system angular momentum similar to that of the Earth-Moon system. Among these, we favor those that leave the Earth > 95% accreted after the Moon-forming impact, implying a giant impactor mass between 0.11 and 0.14 Earth masses.

Back to the Drawing Bored Board

It is not a perfect theory yet. It cannot explain the oxygen-isotope similarity, which does however show they were formed at the same time. But more chemical data is needed, especially how the leftover discombobulated parts came together from almost Mars sized Theia (the name some have given asteroid X).  One might ask about Saturn's disks not solidifying as they are going around it, probe's fly-byes show they are still particles.  Some have problems with a second collision. There is curiosity concerning how Pluto's moon, Charon derived; maybe another impact, since it, unlike other planets, shares this proportionally larger satellite.  If it's evolutionary, why are mostly all the other moons so small.  They want to know whether it was as Ejected Ring Theory proposed, planetesimals like the orbiting asteroids except more unstable.


Ancient Explanations, Tails, Tales, Trails and Talisman

Now sweet Melinda, the peasants call her the goddess of gloom.
She speaks such good English when she invites you up into her room;
And of course you, you're so kind and conscientious and careful not to go to her too soon:
Still she steals your voice and she leaves you howling at the moon!
           --Bob Dylan

While wolves merely howled at the moon, man, since prehistoric times, wanted to tell the story of how it got there. Here are some examples of legends, myths and stories of "Once upon a beginning:"

Judaic (& others)  A Lesser Light by a Creator God
Sumerians           The god Suen
Assyrians            The god Nanna
Babylonians        The god Sîn (derived from Suen)
Arkkadians         The god Sîn
Scandinavia        The Wolves of Ironwood
Ancient Greece   Monsters of the Sicilian Sea
                           The Barely Mother
Ancient Rome     Fana, the Chaste Maid
                           Diana’s Moon Children
Chukchi (Siberia) Ihe Reindeer Maid
Pacific Islands    The seeds of the Aoa
Burma                The Magic Pestle
Japan                  Tsuki-yomi, sister of sun god Amaterasu
China                  Chinese Seed-Birds
                           Moon Toads
                           Yang (wife of Yin)
India                   A Hare in the Moon
                           The Blood of Creation
                           The Lake of the Moon  
                          How the Sun, the Moon, and the Wind Went Out to Dinner
Lithuania            The Parting of the Sun and Moon
Germany             The Tale of Hyuki and Bil (Jack and Jill)
                           The Champion Drinker
                           Mistletoe: the Fruit of the Oak
                           A Man in the Moon
Denmark            The Snow Queen
Algeria               The First Tears
 Nigeria               A Nigerian Moon Tale
Hottentot (S Afr) The origin of the Harelip
Wales                 Talesin, Birth of a Poet
                           Saint Dwnywen’s Ice
                           Sitting on the Moon
 Great Britain     Tales of the Oak Spirit
 Columbia            Moon Waters
Native American
    Pawnee           Wolf Spirit
    Inuits              An Arctic Sea Demon
                            A Lesson of Darkness
    Blackfeet        The Adulterous Moon
    Navajo            Changing Woman

The Big Three Theories (Family Members)


The first seriously considered genesis of the moon was proposed in 1878 by none other than Charles Darwin's son, George Howard.  In this scenario, the early earth's spin caused a huge chunk to veer off the resulting elongation (like it was Play-doh) and become our moon.  This had become known as the 'fission' or 'daughter'.  By 1882 Osmond Fisher convinced many that the Pacific Ocean bed is further evidence of it. In 1936 the US Government Office of Education touted Darwin-Fisher model as fact, including the billion year old date of the event, mentioning this as cause of the Pacific basin. What foils this plan is the Space Missions should have shown that both were from identical components in amounts and type, and it is not the case.  The angular elements have been proven to not be able to come from this proposition.


But, there was another elder competing, and that was 'spouse' or 'capture' theory.  This one had the earth's gravity pulling in some trespassing body, and bringing it in orbit to keep it company.  The sampling of the consistencies of earth and moon show too much differences to allow for this reasoning. There is no explanation for the lunar matter's super kiln fired evidence. Unfortunately for them, the moon is too big to be caught, (like a human catching a boulder.)


Earth's petite twin came about from the same 'batter' or nebulae at the same time in the Solar System's beginning: this is the coaccretion or 'sister' theory. As you read above, (moon's smaller core, no gold or lead: they were vaporized), the new research has put the holes in this Swiss cheese of a moon birth.

(Three Strikes and Yer Out!
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Something moony for the Mad Weeks of May!