Chondrules Suggest Widespread Transport of Rocky Material in the Early Solar System

An image of the protoplanetary disk HL Tauri. Credit: ALMA (ESO/NAOJ/NRAO).  

Our solar system formed from a protoplanetary disk of gas and dust revolving around the young Sun. As the disk cooled, material accreted to form the planets. Isotopic analyses of meteorites distinguish two groups of planetary materials: carbonaceous and non-carbonaceous. It is thought that carbonaceous meteorites formed in the outer solar system, whereas non-carbonaceous meteorites formed in the inner solar system. The timing of formation and growth of the large outer planets, particularly Jupiter, could be responsible for separation of these two different meteorite reservoirs. An early formation of Jupiter would open a gap in the protoplanetary disk and potentially prevent outward diffusive flow of materials, effectively separating the inner solar system from the outer solar system.

Chondritic meteorites are residue of the process of planet formation, hosting primitive materials that escaped accretion into larger planets. Among these materials are chondrules, which are millimeter- to centimeter-sized, once-molten droplets of silicate materials that formed as free-floating objects within the first few million years of solar system history before incorporation into meteorites. A recent coordinated petrographic, chemical, and isotopic analysis of chondrules led by Curtis Williams from the University of California, Davis shows that some chondrules represent the missing link between the two isotopic reservoirs. The chondrules from carbonaceous chondrites include an assortment of materials from the inner as well as outer solar system, suggesting that outward transport of materials did occur in the early protoplanetary disk. As a result, either Jupiter did not form early (or quickly) enough to separate the inner and the outer solar system or the gap created by Jupiter remained permeable to small objects such as chondrules. This new study supports the findings of previous work, including the analysis of comet samples returned by the Stardust mission, that suggest there was a large-scale transport of rocky materials across several astronomical units in the early solar system. READ MORE