Relict olivines in micrometeorites: precursors and interactions in the earth’s atmosphere
N. G. Rudraswami, M. Shyam Prasad, S. Dey, D. Fernandes, J. M. C. Plane, W. Feng, S. Taylor, and J. D. Carrillo-Sánchez
The Astrophysical Journal, Volume 831, Number 2
Published 2016 November 9
“Antarctica micrometeorites (~1200) and cosmic spherules (~5000) from deep sea sediments are studied using electron microscopy to identify Mg-rich olivine grains in order to determine the nature of the particle precursors. Mg-rich olivine (FeO < 5wt%) in micrometeorites suffers insignificant chemical modification during its history and is a well-preserved phase. We examine 420 forsterite grains enclosed in 162 micrometeorites of different types—unmelted, scoriaceous, and porphyritic—in this study. Forsterites in micrometeorites of different types are crystallized during their formation in solar nebula; their closest analogues are chondrule components of CV-type chondrites or volatile rich CM chondrites. The forsteritic olivines are suggested to have originated from a cluster of closely related carbonaceous asteroids that have Mg-rich olivines in the narrow range of CaO (0.1–0.3wt%), Al2O3 (0.0–0.3wt%), MnO (0.0–0.3wt%), and Cr2O3 (0.1–0.7wt%). Numerical simulations carried out with the Chemical Ablation Model (CABMOD) enable us to define the physical conditions of atmospheric entry that preserve the original compositions of the Mg-rich olivines in these particles. The chemical compositions of relict olivines affirm the role of heating at peak temperatures and the cooling rates of the micrometeorites. This modeling approach provides a foundation for understanding the ablation of the particles and the circumstances in which the relict grains tend to survive."