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Earth and Moon do nor share same materials

Date: 11 March 2020 Tags: Space

Issue

The moon and Earth may be more different than previously thought, challenging existing models for how the moon formed, according to a new study.

 

Background

Earth originated about 4.5 billion years ago, and previous research suggested that the moon arose a short time after that.

 

Details

  • For the past three decades, the prevailing explanation for the moon's origin was that it resulted from the collision of two protoplanets, or embryonic worlds. One of those was the newborn Earth, and the other was a Mars-size rock nicknamed Theia.

  • This "giant impact hypothesis" seemed to explain many details about Earth and the moon, such as the large size of the moon compared with Earth and the rates of rotation of the two bodies.

  • The scientists found that there were subtle but regular differences in oxygen isotopic composition depending on the kind of lunar rock tested.

  • Computer models of the giant-impact scenario often say that 70% to 90% of the moon should be made of material from Theia. The problem is that most bodies in the solar system have unique chemical makeups, and so the Earth, Theia and therefore the moon, should too.

  • The rock samples that the Apollo missions returned from the moon show that the natural satellite's composition is uncannily similar to Earth's, much more similar than such models would predict for versions of elements called isotopes.

  • This extreme similarity in isotopes of elements such as oxygen has raised great challenges for the giant-impact scenario. One possibility is that the proto-Earth and Theia were nearly identical to start with when it came to oxygen isotopes, which seems unlikely.

  • Another is that the proto-Earth and Theia's oxygen isotopes were fully mixed in the aftermath of the collision, perhaps due to an impact so violent that it vaporized a large portion of the early Earth.

  • The most important implication from these findings is that giant-impact models no longer have to account for virtually indistinguishable oxygen isotopic compositions between Earth and the moon.

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