New understanding of the formation of the Earth

(ORDO NEWS) — Although the Earth has been studied in detail for a long time, some fundamental questions have yet to be answered.

One of them concerns the formation of our planet, the origin of which researchers still know nothing about. An international research team led by ETH Zurich and the National Center for Research Competence PlanetS proposes a new answer to this question based on laboratory experiments and computer simulations.

“The prevailing theory in astrophysics and cosmochemistry is that the Earth formed from chondrite asteroids. These are relatively small, simple blocks of rock and metal that formed during the early stages of the solar system,” explains study lead author Paolo Sossi, professor of experimental planetary science at ETH Zurich.

“The problem with this theory is that no mixture of chondrites can explain the exact composition of the Earth, which is much poorer in light, volatile elements like hydrogen and helium than we might expect.”

Sossi’s team was looking for a solution. “The dynamic models with which we construct the formation of planets show that they formed gradually in our solar system. Small grains eventually turned into kilometer-sized planetesimals, accumulating more and more material due to gravitational attraction,” Sossy explains.

Like chondrites, planetesimals are also small bodies of rock and metal. But unlike the chondrites, they were hot enough to differentiate into a metallic core and a rocky mantle.

“Moreover, planetesimals that formed in different regions around the young Sun or at different times can have very different chemical compositions,” Saussy adds. Now the question is whether a random combination of different planetesimals can lead to a composition,

To find out, the team ran simulations in which thousands of planetesimals collided with each other in the early solar system. The models are designed in such a way that over time the celestial bodies corresponding to the four rocky planets – Mercury, Venus, Earth and Mars – were reproduced.

Simulations have shown that a mixture of many different planetesimals could lead to the Earth’s effective composition. Moreover, the composition of the Earth is even the most statistically likely outcome of these simulations.

“Even if we suspected something like this, we still consider such a result very remarkable,” recalls Sossi. “Now we have not only a mechanism that better explains the formation of the Earth, but also a benchmark for explaining the formation of other rocky planets,” says the researcher.

This mechanism can be used, for example, to predict how the composition of Mercury differs from that of other rocky planets. Or how rocky exoplanets of other stars might be composed.


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