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The theory would explain Earth’s peculiar chemical composition;
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The resolution can even help tell the story of other planets;
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Researchers believe that the Earth was formed slowly through its gravitational field.
In addition to answering the mystery of how our planet got here, the theory would explain the peculiar chemical composition of Earth. Terra. And it could help tell the history of other planets like ours too.
“The prevailing theory in astrophysics and cosmochemistry is that the Earth formed from chondritic asteroids. These are simple, relatively small blocks of rock and metal that formed early in the solar system,” explains Paolo Sossi, professor of experimental planetology at ETH Zurich.
“The problem with this theory is that no mixture of these chondrites can explain the exact composition of the Earth, which is much poorer in light and volatile elements, such as hydrogen and helium, than we expected,” argued the professor.
Researchers have come up with numerous ideas over the years to explain this, suggesting that collisions of the raw materials that formed Earth generated an enormous amount of heat and vaporized the lighter elements.
However, Earth’s isotopic composition seems to suggest otherwise: “All isotopes of a chemical element have the same number of protons, albeit different numbers of neutrons. Isotopes with fewer neutrons are lighter and therefore should escape more easily,” said Professor Sossi.
“If the theory of vaporization by heating were correct, we would find fewer of these light isotopes on Earth today than in the original chondrites. But that is precisely what isotope measurements do not show.”
Researchers began looking for a better answer. Planets in the Solar System are thought to have formed over time, with smaller grains growing into the planetesimals – small bodies of accumulated gas and dust – accumulating material through their gravitational pull.
Unlike chondrites, planetesimals were heated enough to create a separation between their metallic core and the rocky mantle; moreover, planetesimals formed in different areas around the Sun, or at different times, can have remarkably different chemical compositions.
The team ran simulations of thousands of planetesimals colliding to see if they could produce bodies similar to Mercury, Venus, Earth and Mars. The simulations show that not only could a mixture of many different planetesimals have formed Earth, but that a planet with Earth’s composition is the statistically most likely outcome.
“Even if we suspected it, we still find this result very remarkable,” says Professor Sossi.
“Now we not only have a mechanism that better explains the formation of the Earth, but we also have a reference to explain the formation of other rocky planets”, says the researcher.
“The mechanism could be used, for example, to predict how Mercury’s composition differs from that of other rocky planets. Or how rocky exoplanets from other stars might be composed.”
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