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EI2GYB > ASTRO 23.11.25 17:43l 55 Lines 7591 Bytes #999 (0) @ WW
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Subj: New Research Suggest Earth and Theia were Neighbors Before
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New Research Suggest Earth and Theia were Neighbors Before They Collided
According to the leading theory of how the Earth-Moon system formed (the Giant Impact Hypothesis), a Mars-sized object (named Theia) collided with a proto-Earth 4.5 billion years ago. This turned both objects into molten lava, which eventually coalesced and cooled to form the Earth and Moon. Over time, the Moon migrated outward, eventually reaching its current, tidally locked orbit around Earth, where one side is permanently facing us. For decades, scientists have debated where Theia may have originated, whether it formed in the inner or outer Solar System.
According to new research from the Max Planck Institute for Solar System Research (MPS), Theia and Earth were actually "neighbors" (in the cosmic sense). As they argue in a recently published paper, Theia likely originated in the inner Solar System. Their analysis is based on the examination of ratios of iron isotopes in lunar rocks returned by Apollo astronauts, compared with those found on Earth. This allowed the team to constrain the composition of Theia and trace its origins.
The team was led by Timo Hopp, a geoscientist and Lab Manager with the MPS and the Department of Geophysical Sciences at the University of Chicago. He was joined by colleagues from both institutions, as well as researchers from the Department of Earth and Planetary Sciences at the University of Hong Kong, the CNRS Laboratoire Magmas et Volcans at the Universit‚ Clermont Auvergne, and the Department of Earth and Environmental Sciences at Michigan State University. Their study, "The Moon-forming impactor Theia originated from the inner Solar System," appeared on Nov. 20th in the journal Science.
Scientists first began to suspect that Earth and the Moon formed together when Apollo astronauts returned samples of lunar rock to Earth. These rocks revealed that the Moon's crust was very similar to Earth's, composed predominantly of silicate minerals and metals. Further experiments involving seismometers showed that the Moon also had a similar structure, consisting of a silicate crust and mantle, and an iron-nickel core. This led to the Giant Impact Hypothesis, but questions remained about Theia's size, composition, and its point of origin in the Solar System.
Given Theia's cataclysmic fate and the passage of time, answering these questions is very challenging. Luckily, traces of Theia remain in rocks found on present-day Earth and the Moon, which scientists compare to determine whether they originated from Theia. This is precisely what Hopp and his colleagues did by examining iron isotopes in 15 terrestrial rocks and six lunar samples, comparing them with one another and with several meteorites. The ratios of these isotopes in a body can reveal where it formed, as scientists believe that isotopes of different elements were not likely to have been evenly distributed in the early Solar System.
In short, it is theorized that billions of years ago, when the planets were still forming, isotopes of iron, silica, carbon, and other building blocks occurred in different ratios in the outer Solar System than those found closer to the Sun. In addition to iron isotopes, the team also considered those of chromium, molybdenum, and zirconium. Said co-author Nicolas Dauphas of the University of Chicago and the University of Hong Kong:
Using mass-balance calculations of unprecedented accuracy, their results showed that Earth and the Moon have indistinguishable mass-independent iron-isotopic compositions. This supports earlier isotope-ratio measurements for other elements, including chromium, calcium, titanium, and zirconium, which had already shown that Earth and Moon are indistinguishable in this respect. Unfortunately, these similarities do not support any direct conclusions about Theia, as there are too many possible collision scenarios and unanswered questions about how the collision redistributed its material.
While most models contend that the Moon formed almost entirely from material from Theia, it may be mainly composed of material from the proto-Earth's mantle. Also, there's the possibility that material from Earth and Theia mixed to the point of becoming inseparable. However, the team's results allowed them to consider scenarios based on different compositions of proto-Earth and of Theia, as well as different sizes of Theia. From this, they were able to get a clearer picture of the planets and the impact event, based on how it shaped the Earth-Moon system we see today.
The best-fit scenario they found was that both Earth and Theia originated in the inner Solar System. This was supported by the team's examination of meteorites. Since they are essentially material left over from the formation of the Solar System (and different classes formed in different regions), meteorites can reveal which building materials were available during the early Solar System. Based on the team's analysis, they determined that Theia likely formed closer to the Sun than our planet.
"The most convincing scenario is that most of the building blocks of Earth and Theia originated in the inner Solar System," said Hopp. "Earth and Theia are likely to have been neighbors."
These results provide additional clues as to what the early Solar System looked like. Between the Giant Impact that created the Earth-Moon system, the Late Heavy Bombardment, and how objects kicked from the outer Solar System migrated inward (causing collisions along the way), it seems safe to say that our Solar neighborhood was a rough and violent place! But it was from this destruction and recombination that our planet and its only natural satellite emerged, eventually giving rise to life as we know it. The famous words of Pablo Picasso come to mind: "Every act of creation is first an act of destruction".
Further Reading: Max Planck Institute for Solar System Research
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