Mid-infrared spectroscopy of components in chondrites: Search for processed materials in young Solar Systems and comets

Abstract

We obtained mid-infrared spectra of chondrules, matrix, CAIs and bulk material from primitive type 1–4 chondrites in order to compare them with the dust material in young, forming Solar Systems and around comets. Our aim is to investigate whether there are similarities between the first processed materials in our early Solar System and protoplanetary disks currently forming around other stars. Comparison between the laboratory infrared data and astronomical spectra indicate a general similarity between processed Solar System materials and circumstellar dust. This includes fine-grained matrix material, but also processed component like chondrules and or impact shock processed CM like material. Comets investigated in this study also have spectral features that could allow contents of chondrules or impact shock processed matrix material. Chondrule spectra can be divided into two groups: (1) chondrules dominated by olivine features at ∼11.3μm and ∼10.0μm and (2) mesostasis rich chondrules that show main features at ∼10μm. Bulk ordinary chondrites show similar features to both groups.Fine-grained matrix is divided into three groups: (1) phyllosilicate-rich with a main band at ∼10μm, (2) olivine-rich with bands at 11.3μm and ∼10μm, and (3) pyroxene-rich with several peaks between 9.3μm and 11.2μm. Impact shock-processed matrix from Murchison (CM2) shows features from phyllosilicate-rich, amorphous and olivine-rich material. CAIs show melilite/spinel-rich features between 10.2μm and 12.5μm.Astronomical spectra are divided into four groups based on their spectral characteristics – amorphous (group 1), pyroxene-rich (group 2), olivine-rich (group 3) and ‘complex’ (group 4). Group 2 is similar to enstatite-rich fine grained material like e.g. Kakangari (K3) matrix. Groups 3 and 4 can be explained by a combination of varying concentrations of olivine and mesostasis-rich chondrules and fine-grained matrix, but also show very good agreement with shock processed material. Comparison of band ratios confirms the similarity with chondritic material e.g. for HD100546, while the inner disk of HD142527 show no sign of chondrule material.For some systems, though, we find that other amorphous materials such as IDP/GEMS have to be taken into account to fully fit their spectra.