July 8. () –
An international research team led by ETH Zurich proposes a new theory for the formation of the Earth. It can also show how other rocky planets formed.
Although the Earth has been studied in detail for a long time, some fundamental questions remain unanswered. One of them refers to the formation of our planet, about whose beginnings researchers are still unclear.
An international research team led by ETH Zurich and the National Center of Research Competence PlanetS is now proposing a new answer to this question based on laboratory experiments and computer simulations. The researchers have published their study in the journal Nature Astronomy.
“The prevailing theory in astrophysics and cosmochemistry is that the Earth formed from chondritic asteroids. These are relatively small and simple blocks of rock and metal that formed in the early stages of the solar system,” he explains. it’s a statement the lead author of the study, 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, volatile elements like hydrogen and helium than we would have expected.”
Over the years several hypotheses have been proposed to explain this discrepancy. For example, it was postulated that the collisions of the objects that later formed the Earth generated enormous amounts of heat. This vaporized the light elements, leaving the planet in its current composition.
However, Sossi is convinced that these theories become implausible as soon as the isotopic composition of the different elements on Earth is measured: “All isotopes of a chemical element have the same number of protons, although different numbers of neutrons. Isotopes with fewer neutrons are lighter and therefore should be able to escape more easily.If the heating vaporization theory were correct, we would find fewer of these light isotopes on Earth today than in the original chondrites. But that’s precisely what the isotope measurements don’t show.”
Therefore, Sossi’s team looked for another solution. “Dynamic models with which we simulate planet formation show that the planets in our solar system formed progressively. Small grains became kilometre-sized planetesimals over time as more and more material accumulated through their attraction. gravity,” explains Sossi.
Like chondrites, planetesimals are also small bodies of rock and metal. But unlike chondrites, they have heated up enough to differentiate into a metallic core and mantle rock. “Furthermore, planetesimals that formed in different areas around the young Sun or at different times can have very different chemical compositions,” adds Sossi. The question now is whether the random combination of different planetesimals really does result in a composition that matches that of Earth.
To find out, the team ran simulations in which thousands of planetesimals collided with each other in the early solar system. The models were designed in such a way that, over time, celestial bodies corresponding to the four rocky planets Mercury, Venus, Earth and Mars were reproduced. The simulations show that a mixture of many different planetesimals could lead to the effective composition of the Earth. Furthermore, the composition of the Earth is even the statistically most likely outcome of these simulations.
“Although we suspected it, we found this result very remarkable,” recalls 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 the other rocky planets”, says the researcher. The mechanism could be used, for example, to predict how Mercury’s composition differs from that of the other rocky planets. Or how rocky exoplanets from other stars might be made up.
“Our study shows how important it is to consider both dynamics and chemistry when trying to understand planetary formation,” says Sossi. “I hope that our findings will lead to closer collaboration between researchers in these two fields.”
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