A new work published in Science provides crucial clues about Theia and the origin of the MoonThe protoplanet that collided with the young Earth would have formed in the inner solar system, possibly even closer to the Sun than our own world.
The investigation, with the participation of University of Chicago (USA) and the Max Planck Institute The German Solar System Research Institute (Germany) reconstructs the chemical puzzle of the Earth-Moon system without falling into triumphalism: it offers a clearer picture, but makes it clear that further work will be needed. more samples and analysis to close the case completely.
Isotopic fingerprinting and method
The team examined with great precision the iron isotopic signatures in rocks from the Moon and Earth, that is, the different versions of the same element according to their number of neutrons, which act as markers of the place of formation.
Were analyzed six lunar samples brought back by the Apollo and 15 terrestrial rockscomparing them to meteorites that represent chemical reservoirs of the protoplanetary disk. The similarity between Earth and the Moon is overwhelming in Fe, a key clue about its common kinship.
These brands fit with the non-carbonaceous meteorites, typical of the interior of the solar system, and deviate from the patterns expected for materials from cooler outer regions.
To refine the origin, the authors integrated records of other elements sensitive to planetary differentiation processes, such as chromium, molybdenum and zirconium (in addition to calcium and titanium), and applied mass balance calculations that allow us to go back from the current state to the composition prior to the major impact.
With this “reverse engineering” approach, the dataset discriminates between plausible scenarios and discards combinations that do not reproduce the isotopic equality observed between the Earth and its satellite.
Theia, a neighbor of the inner solar system
The results indicate that the iron isotope ratios The materials from proto-Earth and the Moon are virtually indistinguishable and consistent with materials formed in the internal region of the solar system, which strongly narrows down Theia's birthplace.
By combining the traces of various elements with the modeling, the most consistent scenario is that Theia originated even closer to the Sun than Earth. In other words, both worlds were neighbors that grew in the same area before the collision that gave rise to the Moon.
The analysis also suggests that some of Theia's composition doesn't quite fit with known types of meteorites, a sign that it incorporated material that is little represented in our collections, typical of very internal regions of the solar disk.
The geochemical story adds up: long before the impact, iron and molybdenum They sank towards the Earth's core; the iron present today in the mantle requires a subsequent external input, for which Theia appears as the most likely source.
This framework revises models that placed Theia in distant, cold regions capable of providing water. If most of the ingredients came from interiorIt is advisable to reassess how and when The volatile ones arrived to the primitive Earth.
Implications and open questions
The work reinforces the big impact hypothesisAbout 4.500 billion years ago, a Mars-sized body collided with the proto-Earth, and the debris eventually formed the planet. Moon, after an intense mixing of the mantles of both planets.
Even so, pieces are still missing. They haven't been identified. unequivocal remains The exact proportion of Theia's material in the Earth-Moon system is still under study. Different hydrodynamic models of the impact may produce similar results in isotopes.
The authors advocate for expanding the catalog of lunar samples of little-explored regions and by improving the accuracy of additional elements, which will allow us to refine the chemical portrait of the episode that shaped our satellite.
The European role is prominent: the contribution of the Max Planck Institute underlines the boosting science in Europe when reinterpreting key episodes of planetary formation using state-of-the-art analytical techniques.
Nevertheless, the essential points are clearly defined: the chemistry of lunar, terrestrial, and meteoric rocks It supports the idea that Theia and proto-Earth formed as neighbors in the inner solar system, and that their collision not only gave birth to the Moon but also helped define the composition and dynamics of the planet where we live.
