Different planets have different oxidation states. For example, the Earth’s crust and mantle are very oxidized, while the Moon and Mars are much more reduced. This is important because the oxidation state of a planet plays a role in its geological and biological evolution. It influences how elements are segregated within a planet and the composition of a planet’s atmosphere, which is critical for supporting life. Previous studies have suggested that a planet’s oxidation state might have been established very early in its history, when the planet was still dominated by a magma ocean. A recent research endeavor, led by Jie Deng from Yale University, studied the mechanisms that control the oxidation state of magma oceans by combining first-principles simulations with thermodynamic modeling applied to early Earth, Mars, and the Moon.
These models demonstrated that the size of a body influences its oxidation state; a smaller planet will produce a shallower magma ocean (less pressure) than a larger planet (more pressure). A magma ocean on Earth should therefore be more oxidized, especially near the surface, while a magma ocean on the Moon would be the most reduced, and Mars would fall in between. The results of this modeling are consistent with modern-day data, implying that the current oxidation states of planets were inherited from their early magma oceans. These models also predicted that Earth would have developed a primitive atmosphere that contained an abundance of water and carbon dioxide because it had a more oxidized magma ocean. In contrast, the very reduced lunar magma ocean would have formed an atmosphere containing molecular hydrogen and carbon monoxide. Mars, with its intermediate oxidation state, would have had an atmosphere that contained all gas species, but water and molecular hydrogen likely dominated. The development of these distinctively different early atmospheres likely influenced the subsequent geological and biological evolution of these bodies and what we observe today. READ MORE