(ORDO NEWS) — In fact, none of us knows exactly how our planet formed. We have the general idea, but the finer details are much harder to figure out.
There is a well-known model according to which the Earth was formed as a result of a gradual accumulation of asteroids. However, even here there are some points that are difficult to explain.
A new study has revealed a new formation process that matches Earth’s characteristics 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 stone and metal that formed early in the solar system,” said planetary scientist Paolo Sossi from 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 expected.”
The process of planet formation raises many questions, but scientists have been able to piece together the 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 collects into a disk that orbits and wraps around the growing star.
This disk of dust and gas not only contributes to the growth of a growing star – the small densities within this vortex also coalesce into smaller, cooler clusters.
Small particles collide and stick together, first electrostatically, then gravitationally, forming larger and larger objects that can eventually turn into a planet. This is called the accretion model, and it is fully supported by the observational data.
But if the stones that stick together are chondrites, that leaves open the big question of missing lighter, volatile elements.
Scientists have put forward various explanations, including the heat generated during the collisions, which could vaporize some of the lighter elements.
This, however, is also not necessarily tracked: according to recent experimental work led by Saussy, heat would evaporate the lighter isotopes of elements with fewer neutrons. But lighter isotopes are still present on Earth in roughly the same proportions as in chondrites.
Saussy and his colleagues decided to explore another possibility because the rocks that coalesced to form the Earth were not chondrite asteroids from Earth’s general orbital neighborhood, but planetesimals.
These are the larger bodies, the “seeds” of the planets, which have grown to a size large enough to have a core.
“The dynamical models with which we model the formation of planets show that the planets in our solar system formed gradually.
The small grains evolved over time into kilometer-sized planetesimals, accumulating more and more material under their gravitational pull,” Saussy said.
“Moreover, planetesimals that formed in different regions around the young Sun or at different times can have very different chemical compositions.”
They ran simulations of the Nth body, changing variables such as the number of planetesimals in a scenario in which the 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 an extremely disturbing effect on the smaller rocks orbiting around, scattering planetesimals into the inner disk.
The simulation was designed 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. In fact, 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 changing composition 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 found this result very remarkable.
Now we not only have a mechanism that better explains the formation of the Earth, but we also have a link to explain the formation of other rocky planets,” Sossi said.
“Our study shows how important it is to consider both dynamics and chemistry when trying to understand planet formation.
I hope that our results will lead to closer collaboration between researchers in these two fields.”
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