Two new studies have looked into the formation of rocky planets like Earth and Mars and discovered that the chemical composition of planets is dictated by the hellish conditions of their evolution.
According to the research, as planets grow through the accretion of material from a planetary nebula, they collide with a significant fraction of large bodies. These collisions generate heat, which leads to a molten planet with magma oceans and an atmosphere of vaporized rocks. As long as the planet is smaller than Mars this atmosphere will escape into space.
Both studies are published in Nature. The first one focus on the theoretical side of planetary formation. To study what the primordial Solar System was made of, planetary scientists use chondrite meteorites, meteorites made of stony non-metallic materials like rocky planets.
However, the way these meteorites are structured is very different to planets, where chemicals tend to be distinct, so it was not clear how the planets attain such a different structure. The process might be due to the violent process of how they form, or if there were differences in the primordial nebula. The study points the finger at the former, suggesting 40 percent of Earth’s mass might have been lost due to this mechanism.
“Our work changes our views on how planets attain their physical and chemical characteristics," Dr Remco Hin, lead author of the first study from the University of Bristol, said in a statement. “While it was previously known that building planets is a violent process and that the compositions of planets such as Earth are distinct, it was not clear that these features were linked.”
“We now show that vapour loss during the high-energy collisions of planetary accretion has a profound effect on a planet's composition.”
The findings are linked to the amount of magnesium found in planets and asteroids. Earth, Mars, and asteroid Vesta have different magnesium isotopes ratios, suggesting that the value was shaped by the differences in collision history.
The second study, also published in Nature, comes from the University of Oxford and provides experimental backing to the first study's hypothesis. The researchers melted rock and looked at which elements would become volatile. They proposed impacts, especially the gigantic one that created the Moon, as the cause for Earth’s chemical composition.