Article by: Andacs Robert Eugen, on 09 July 2022, at 11:59 am Los Angeles time

This new theory can explain the unusual chemical composition of the Earth, and it could reveal the stories of other planets.

"The predominant theory in astrophysics and cosmochemistry is that the Earth was formed from chondritic asteroids. These are relatively small, simple blocks of rock and metal that formed early in the Solar System," explained Paolo Sossi, professor of experimental planetology at ETH Zurich.

"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 and volatile elements, such as hydrogen and helium," he said.

Researchers have come up with many ideas over the years to explain this, suggesting that the collisions of the raw materials that formed the Earth generated a huge amount of heat and vaporized the lighter elements.

However, the isotopic composition of the Earth suggests something else: "The isotopes of a chemical element all have the same number of protons, although a different number of neutrons. Isotopes with fewer neutrons are lighter and therefore should be able to escape more easily," said Professor Sossi.

"If the theory of vaporization by heating were correct, we would find fewer of these isotopes of light on Earth today than in the original chondrites. But this is not exactly what the isotope measurements show ", the professor continued.

Researchers have begun to look for a better answer. It is believed that the planets in the Solar System formed over time, with smaller granules growing into planetesimals - small bodies of accumulated gas and dust - by accumulating material through their gravitational attraction.

Unlike chondrites, planetesimals were heated enough to create a separation between their metal core and the rocky mantle. In addition, planetesimals formed in different areas around the Sun or at different times can have surprisingly different chemical compositions.

The team performed simulations of the collision of thousands of planetesimals to see if they could produce bodies similar to Mercury, Venus, Earth, and Mars. The simulations show that not only a mixture of many different planetesimals could have formed the Earth, but also that a planet with the composition of the Earth is the most likely result from a statistical point of view.

"Now not only do we have a mechanism that better explains the formation of the Earth, but we also have a reference to explain the formation of the other rocky planets. The mechanism could be used, for example, to predict how Mercury's composition differs from that of other rocky planets. Or how the rocky exoplanets of other stars could be composed ", the professor added.