Collision with Earth 4.5 billion years ago: Theia was previously a neighbor
A protoplanet crashed into Earth more than four billion years ago, ejecting the Moon. It is now clear where the protoplanet came from.
Artistic representation of the collision of the early Earth with Theia
(Image: © MPS / Mark A. Garlick)
The giant protoplanet Theia, which collided with Earth 4.5 billion years ago, originated from the inner solar system and likely formed closer to the sun than Earth. This was discovered by a research group led by the Max Planck Institute for Solar System Research based on an extensive isotope analysis. For this, the origin of iron on Earth was also investigated with unprecedented accuracy. It turned out that this ubiquitous metal today could mainly originate from Theia, meaning it was brought to the already-formed Earth later.
Isotopes illuminate Earth's history
The collision with Theia was probably the most consequential event in the history of our home planet, and the material from which the Moon formed was also ejected during this event. The analysis now presented has confirmed this once again; in terms of isotopic ratios, the 15 samples of typical Earth rock and six from the Moon examined are “indistinguishable.” This has proven their common origin once more, but at the same time, the finding provided no clues about Theia, the research institution writes. To achieve this, the team had to extensively simulate which compositions and sizes of Theia and the early Earth could have led to the current system of Earth and Moon.
According to the Max Planck Institute, the research group not only focused on iron isotopes but also on those of chromium, molybdenum, and zirconium. All provide information about different epochs of Earth's history. The isotopic ratios of Theia's material therefore differ significantly from those on Earth and are thus still identifiable today. The analysis yielded several possible scenarios, but based on our knowledge of planet formation and the composition of meteorites, it was possible to conclude specifically “that Theia must have originated from the inner part of the early solar system, closer to the sun than the current Earth's orbit.”
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In recent years, research into the consequences of the giant collision has made significant progress, with Thorsten Kleine, now director of the Max Planck Institute for Solar System Research, repeatedly involved. Six years ago, he and a research group determined that a large part of our comparatively abundant water reserves could have come to Earth during the collision. Later, another team determined that two giant structures deep within the Earth could be remnants of Theia. Only a few months ago, the impact was noticeably dated backwards. The new work has now been published in the scientific journal Science.
(mho)
