New Study Shows Deformation of First Formed Solids in Our Solar System Resulted from Nebular Shocks
August 2, 2022
X-ray false color composite map of the CAI showing Mg in red, Ca in green, and Al in blue, illustrating that the CAI is enriched in refractory elements calcium and aluminum, compared to the meteorite matrix seen in red. Credit: Mane et al., 2022.
A recent study reports evidence of deformation in the oldest solids formed in our solar system resulting from nebular shocks. The results of this work suggest that these shocks may have been active and more widespread in the early solar system than previously thought. The study was published in Geochimica et Cosmochimica Acta.
Calcium-aluminum-rich inclusions (CAIs) are millimeter- to centimeter-sized objects hosted in primitive meteorites. They are the oldest solids to have condensed from the nebular gas and, therefore, preserve records of the earliest chemical and physical processes. A recent study of a CAI from NWA 5028 CR2 chondrite suggests that some CAIs may have experienced nebular shocks at early stages of the solar system history.
"CAIs are made of minerals forming at high temperatures, rich in refractory elements such as calcium and aluminum. Radiometric dating of CAIs and their components suggest that majority of these inclusions formed within the first million years of our solar system history and thus preserve the snapshots of the earliest events at the very beginnings of our solar system," says Prajkta Mane, lead author of the study, and a Universities Space Research Association scientist at the Lunar and Planetary Institute.
"These CAIs represent, to the best of our knowledge, the first solids that formed in the solar system. We believe that they experienced large-scale transport in our early solar nebula and witnessed a range of physical and chemical processes over their lifetimes. This study is the first to constrain timescales with physical processing by shockwaves," says Tom Zega, a coauthor of the study.
A coordinated analysis of a CAI hosted in a carbonaceous chondrite revealed intensely deformed microstructures in melilite and spinel, suggesting that it was shocked at an elevated ambient temperature. Further time constraints on this event, placed by 26Al-26Mg short-lived chronometry, revealed that the shock event occurred very early, within the first few hundred thousand years of the solar system history. Nebular shock waves are thought to be responsible for the melting of chondrules, major chondritic components rich in ferromagnesian minerals. However, shock deformation in CAIs implies that nebular shocks may have been more common in the early solar system than previously thought. Many studies using optical microscopy and transmissions electron microscopy have reported that CAI melilite shows microstructures consistent with significant strain and deformation, providing some clues about their tortured past. The EBSD analytical technique provides a more comprehensive and quantitative view of this deformation. "The microscopy techniques combined with the isotopic analysis provide a holistic understanding of these events," said the study's lead author, Prajkta Mane.
The results of this work imply that nebular shocks were active in the solar system on a large spatial extent, from 0.1 au to all the way beyond Jupiter. Additionally, these nebular shocks were active very early, at the beginning of the solar system. The astrophysical mechanisms causing these nebular shocks remain elusive, and further studies of primitive meteoritic components and samples returned from primitive asteroids, combined with astrophysical models, are needed to understand the extent of nebular shocks during early planet formation.
This work was in collaboration with the Lunar and Planetary Institute (USRA), Arizona State University, University of Arizona, and EDAX Ametek.