New Theoretical Models Salvage Moon-Forming Impact Theory


Theia impacting proto-Earth, image by Fahad Sulheria.

One of the widest accepted models for the Moon’s formation states that a renegade, Mars-sized planet, named Theia, slammed into Earth 4.5 billion years ago, and pushed up debris that would eventually coalesce into a satellite. This theory has been able to predict and explain many facts, like the mass of Earth and the Moon, but it also says that most of the lunar-forming debris stemmed from Theia, not proto-Earth. Theia is thought to have originated from a different part of the Solar System, with different elemental isotopes, which conflicts with some of the more sensitive measurements of the past decade showing that rocks from Earth and the Moon have identical isotopic ratios of oxygen, titanium, chromium, and tungsten.

Two teams of researchers report that they have solved this chemical quandary and have been able to uphold this lunar origin theory. The two papers predict different sizes for Theia. One paper states that Theia was smaller than Mars, and another says that Theia was four to five times larger than Mars. Both papers were published in the journal Science (1, 2).


The Moon-forming impactor may have been four or five times the size of Mars, or much smaller, according to new models. Image: DetlevvanRavenswaay/Science Photo Library.

These papers show that there is a wide variety of impact scenarios that were possible. The teams assumed that Earth rotated twice as fast as it does now. Gravitational interaction between the Moon and Sol could have drained the spin of a rapidly rotating Earth.

Robin Canup, one of the originators of the Mars-sized impact model, now considers the possibility that proto-Earth with half of Earth’s current mass collided with an impactor of similar mass. The collision would have mixed the isotopic composition of the debris, making the isotopic composition indistinguishable from either body. It would have also revved up Earth’s spin, which could have drained in a similar fashion to the other study.

The gravitational mechanism known as evection resonance appears when the short axis of the Moon’s elliptical orbit around Earth precesses in sync with Earth’s orbit around the Sun. Some of the angular momentum from a rapidly spinning Earth would be transferred to the Moon, which in turn allows the rotational energy to be absorbed by the Sol.

Other theorists believe making alterations to the impactor’s speed and angle of impact, rather than its size, may result in a plausible Moon forming theory.

[via Nature]

4 Comments on "New Theoretical Models Salvage Moon-Forming Impact Theory"

  1. Madanagopal.V.C. | October 20, 2012 at 11:10 am | Reply

    In one of the articles published by me under ” SCIENCE FRONTIERS – A PROBE BY MADAN “,I have clearly indicated that Moon is alien to Earth and it had got to be formed or captured from Kuiper belt going around the Sun bringing along with its numerous comets, that are rocks , planetoids and water borne through ice mountains. I had stressed these points in many of my comments relevant to the subject in sci-tech daily also. The article substantiates my hypothesis. I will elucidate the proof as follows. The asteroid belt next to Mars comes after giant ringed gas planets of Neptune, Uranus, Saturn and and Jupiter. Many of the planetoids even measurable to the size of the earth like Titan had been either devoured or captured in the orbital rings of Neptune, Uranus, Saturn and Jupiter, which make multiple and very many satellites around them. Some of the planetoids had escaped the gravity of Jupiter and Saturn and travelled further towards the Sun. The surviving terrestrial planets were Mars, Earth, Venus , Mercury and two odd shaped stone-mountain like moons of Mars viz., Phobos and Deimos, and our own black soiled Moon. Other debris formed as big asteroid belt after Mars which are sending rocks of mateors to impinge on Mars, Earth, Moon, Venus and Mercury constantly for eons. Now regarding the structure of these planets, one can observe that Earth and Mars look alike in soil chemistry. Moon and Mercury resemble in soil chemistry. This clearly indicates that our Earth was alone 4.5 billion years ago until lt got its companion after its impact with the planetoid Theia. Same may be the case of Mars also. Water found on Moon, Mars and all these planetoids including Titan were imported from extra-planetary impacts. That Moon was never formed out of earth, is proved.Gravitational locking of the Moon with the Earth and to some extent Venus, and over locked Mercury to make retrogade motion is a matter of gravity of the Sun in addition to the impacts. Let us make further research in the Planetary history to get the truth. Thank You.

  2. Why do the moons of Jupiter and Saturn also not rotate?? yet unlike earth do not have “oceans” and so what explains their ” locking”.. the core!
    Tidal locking is said to be the reason that the moon always has the same face towards earth. Jupiter and Saturn have 62 – 63 moons most of which are also in synchronous orbit. In the absence of a liquid ocean and the crustal structure of the earth how do they still pull this off?
    The moon influences tide, thats as far as it goes!
    It is the movement of the surface of the earth, speeding over the core, a conductor covering over a magnet that creates induction of the crust/ocean and movement of the oceans. It is to the magnetic core that moons are locked or pinned to orbit by “flux pinning”, not tidal forces!

  3. Madanagopal.V.C. | October 22, 2012 at 11:33 am | Reply

    Gravitational locking is a gravitational phenomena. Tidal waves of ocean contributes only little to the gyration effect. Even planet Mercury which is devoid of any oceans also got locked by Sun`s gravity to such an extent that it stopped completely and then started rotating in reverse gear. Well! Jupiter is a failed star and it is 10000 times bigger than earth. These giants will naturally lock all its moons gravitationally because they are all small pebbles for its size to get locked gravitationally. I never mentioned tidal force responsible for gravitational locking. Please go through once again. Farther it is from Sun any planet will rotate fast and nearer the Sun brake will be applied. Mars rotates twice as fast as earth and the great Jupiter rotates on its axis in just 10 hours. Earth`s core or for that matter any terrestrial planet which is spherical in size keeps its ionic core and hot magma electrified only to effect magnetism and cause tectonic plate movements which is common not only on earth but also on Moon, Mars etc. For tectonic plates of continents the great oceans are just spoonful of water. Thank YOu.

  4. Earth was formed earlier than some other planets when the sun was still developing and circumstellar disc turns around it. Theia was not big in size and did not have the ability to flatten earth by the impact. Earth surface was partially melt with its early basaltic material. When the pact happened Theia intruded inside the earth ejecting debris to the space as there was no aosphere at that period. The debris coalesced from earth surface and Theia components forming a moon freed fr earth gravity and joined the circumstellar disc around the sun. Because of the intruding Theia inside the earth it’s gravity was not stable. When the sun turned into a main sequence star it released gigantic radio active solar storm pushing away all the debris and rocks within the previous circumstellar disc including the moons. Our moon hit a big rock close to earth and both were attracted by earth gravity starting its wobble movement around the earth at a time Theia large rock resided at the center of the earth

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