About 4.5 billion years ago, there was something of the size of Mars that collided with a newly formed Earth. The object might have fused with Earth and primed it for life, but it also broke a large chink that eventually became the Moon.
Traces of Theia in the Moon
This story is known as the giant impact hypothesis, and the Mars-sized object is called Theia. For the very first time, experts believe that they have found traces of Theia in the Moon.
This hypothesis has been the favored model for explaining the formation of the Moon for years.
“This model was capable of accounting for the then-recent observations from samples returned by the Apollo missions, which included the Moon’s low iron content relative to Earth, depletion in volatiles and enrichment in refractory elements, while avoiding most of the pitfalls of previous lunar origin theories,” researchers from the University of New Mexico wrote in their paper.
More models have predicted that about 70 to 90 percent of the Moon should have been made up of mooshed and reformed Theia, how ScienceAlert puts it.
It’s been also revealed that the oxygen isotopes in the lunar samples that are collected by Apollo astronauts were really similar to the terrestrial oxygen isotopes, and they are very different from the oxygen isotopes on other Solar System objects.
Earth and Theia might have had similar compositions
ScienceAlert notes that there’s one possible explanation: Earth and Theia have similar compositions to begin with.
Another explanation is the fact that everything got mixed during the impact, but it seems that this is not so likely, according to simulations.
“We show,” experts wrote in their paper, “that the method of averaging together lunar isotope data while ignoring lithological differences does not give an accurate picture of the differences between the Earth and Moon.”