Scientists decipher early evolutionary history of the solar system from meteorites

Meteorites, as “guests” from outside, are fragments of asteroids or comets. They contain a wealth of information about the early formation of the solar system, and scientists have collected and studied these “visitors from space” to uncover the formation and evolution of the early solar system.

Recently Prof. LIU Beibei of the School of Physics at Zhejiang University and his collaborators at the University of Copenhagen in Denmark and the University of Lund in Sweden proposed that the formation of the protoplanetary disk can generate a dichotomy of isotopic composition, and based on this they constructed a new model for the formation of celestial bodies in the early solar system. This finding was published in the April 22 issue of the magazine scientific progress†

Meteorites were formed at the beginning of the solar system when a protoplanetary disk, which was the cradle of planets and meteorites, existed around the scorching sun. Meteorites exhibit a dichotomy of isotopic composition between non-carbonaceous (NC) and carbonaceous (CC) groups, indicating that planetesimal formation in the Sun’s protoplanetary disk occurred in two different reservoirs.

This isotopic composition dichotomy also sparked speculation about the early evolution of the solar system in academia. To explain this phenomenon, LIU Beibei et al. focused on the gas in the protoplanetary disk. They found that solid particles, affected by gaseous outflow, migrated at different speeds and in different directions. The simulation results indicated that it would take three million years for CC particles in the outer disk to migrate to the formation region of the inner terrestrial planet. Before entering, the parent bodies of meteorites growing in this area formed via accretion of refractory material. CC meteorite parent bodies formed in the outer disk and grew via charcoal particle accretion. After about three million years, CC particles finally migrated to the inner disk. Since then, terrestrial planets such as Earth and Mars have grown due to the accretion of CC particles. As a result, their isotopic content is a mixture of two primary types of solid. “More importantly, this model predicts that the isotope variations in different meteorites are not spatial separation, but temporal evolution,” noted Prof. Liu.

In this study, LIU Beibei et al. pointed out the flaws of previous theories. Some researchers have argued that the rapid formation of Jupiter and the opening of the opening in the protoplanetary disk could explain the aforementioned phenomenon. The opening of the orbit occurs when the planet is large enough and the gravitational effect is strong enough to remove the gas from around its orbit. This model requires that Jupiter’s solid core formed rapidly within a million years of the formation of the solar system. “If Jupiter could indeed open a deep trench in the disk and completely block the incoming flow of subsequent solids, solid materials in the inner and outer disks would be isolated from each other on their own. And NC solids in the inner disk would become depleted due to rapid migration, however, meteorite dating studies found that NC meteorite parent bodies formed between two and three million years after the formation of the solar system.

“Previous studies have suggested that the isotope dichotomy is a byproduct of the formation of the largest planet in the solar system. But we found it difficult to account for the age and isotope content of the meteorites in the solar system,” explained Prof. Liu, adding that scientific research involves constantly breaking the established mindset.