(ORDO NEWS) — Do you want to know something funny? In fact, we do not know how our planet formed. We have a general idea, but the finer details are much more difficult to unravel.
We have a model that is currently considered the most likely explanation: Earth was formed by the gradual merger of asteroids. However, even here there are some facts about the formation of our planet that are difficult to explain.
In a new work that combines experiments and simulations, a new formation path has been found that matches the characteristics of the Earth much more closely.
“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 early in the evolution of the solar system,” says planetary scientist Paolo Sossi of ETH Zurich in Switzerland.
“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 might expect.”
The process of planet formation raises many questions, but scientists were able to paint a big picture. When a star forms from a dense clump of matter in a molecular cloud of dust and gas in space, the material around it folds into a disk that orbits and wraps around the growing star.
This disk of dust and gas not only forms the waist of a growing star – the small, dense particles inside this vortex also coalesce into smaller, colder clumps.
Small particles collide and grapple with each other, first electrostatically and then gravitationally, forming ever larger objects that can eventually grow into a planet. This is called the accretion model, and it is strongly supported by observational data.
But if the rocks stuck together are chondrites, then the question of the missing light, volatile elements remains open.
Scientists have put forward various explanations, including the heat generated by the collisions, which could vaporize some of the lighter elements.
However, this is not necessarily confirmed: the heat should have evaporated the lighter isotopes of the elements, with fewer neutrons, according to recent experimental work led by Saussy. But lighter isotopes are still present on Earth in roughly the same proportions as in chondrites.
So Saussy and his colleagues decided to explore another possibility: that the rocks that formed the Earth were not chondrite asteroids from the Earth’s general orbital region, but planetesimals. These are the larger bodies, the “seeds” of the planets, which have grown to a size large enough to have a differentiated core.
“The dynamical models with which we model the formation of planets show that the planets in our solar system formed gradually. Small grains eventually turned into kilometer-sized planetesimals, accumulating more and more material due to their gravitational pull,” Saussy said.
“Moreover, planetesimals formed in different regions around the young Sun or at different times can have very different chemical compositions.”
They ran N-body simulations, changing variables such as the number of planetesimals, in a Big Tack scenario in which baby Jupiter first approaches the Sun and then returns to its current position.
In this scenario, the motion of Jupiter in the early solar system had a highly disturbing effect on small rocks orbiting around, scattering planetesimals in the inner disk.
The simulations aimed to create the inner solar system we see today: Mercury, Venus, Earth and Mars. The team found that a diverse mixture of planetesimals with different chemical compositions could replicate the Earth as we see it today. Moreover, the Earth was the most likely outcome of the simulation.
This could have important implications not only for the Solar System and the understanding of the various compositions of the rocky planets within it, but also for other planetary systems elsewhere in the Galaxy.
“Despite the fact that we suspected it, we still consider this result very remarkable. 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,” Saussy said.
“Our study shows how important it is to consider both dynamics and chemistry when trying to understand planet formation. I hope our results will lead to closer collaboration between researchers in these two fields.”
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