Scientists shed new light on how Earth formed | TechNews

An international team of researchers led by ETH Zurich has proposed a new theory of Earth’s formation that may also explain how other rocky planets formed. The research was published in the journal Nature Astronomy.

Lead author Paolo Sossi, a professor of experimental planetology, pointed out that the prevailing theory in astrophysics and cosmochemistry is that Earth is composed of chondrite asteroids (chondritic asteroids), which are small, simple rock-metal clumps that formed in the early solar system. However, the mixture of these chondrites could not explain the exact composition of the Earth, which contains less light, volatile elements such as hydrogen and helium than expected.

Over the years, various hypotheses have been proposed to explain this discrepancy, such as the hypothesis that objects hitting the Earth generated a lot of heat, vaporizing the light elements, leading to the planet’s current composition.

But Sossi points out that isotopes of elements all have the same number of protons but different numbers of neutrons. Isotopes with fewer neutrons are lighter and therefore more likely to escape. If the heating-vaporization theory is correct, fewer light isotopes would be found on Earth today than in primitive chondrites, but measurements don’t show that.

So the Sossi team looked for another solution. The dynamic model of planet formation indicates that the planets of the solar system are formed gradually. Over time, dust particles gravitationally accreted each other and gradually turned into kilometer-scale planetesimals. Like chondrites, planetesimals are small bodies of rock and metal, but are heated enough to differentiate into layered structures with metallic cores and rocky outer shells. What’s more, planetesimals formed at different times in different regions around the young sun may have very different chemical compositions. Do random combinations of planetesimals of different compositions really lead to the same composition as Earth?

The simulation results show that thousands of planetesimals collided with each other in the early solar system, and as time increased, celestial bodies appeared, corresponding to the four rocky planets Mercury, Venus, Earth and Mars.

(This article is reproduced with permission from the Taipei Planetarium; the first picture is a schematic diagram of the formation of the Earth, with a chondrite asteroid on the left and a microplanet on the right. Source: ETH Zürich)