Mystery of moon's formation may have been solved

/ Source:

By Charles Q. Choi,

The moon may have formed after a giant Mars-size rock hit a magma-covered newborn Earth, a new study finds.

Earth came together about 4.5 billion years ago, and previous research suggested the moon arose a short time later. For the past three decades, the prevailing explanation for the moon’s origin was that the moon 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 called Theia, named after the mother of the moon in Greek myth. The moon then coalesced from the debris.

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 rotation rates of the two bodies. However, in the past 15 or so years, evidence has emerged to challenge it and suggest a multitude of alternatives.

Related: How the Moon Formed: 5 Wild Lunar Theories

Computer models of the giant-impact scenario often say that more than 60 percent 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 Earth, Theia and therefore the moon should also. However, rock samples from the moon show its composition is uncannily more similar to Earth than such models would predict when it comes to versions of elements called isotopes. (Isotopes of an element each have different numbers of neutrons.)