Characterizing Spectral Diversity in Carbonaceous Chondrites and Linking to Asteroids with Microimaging Spectroscopy

Abstract:

Primitive asteroids record alteration processes in the early Solar System; however, telescopic visible and shortwave infrared (VSWIR) spectroscopy of primitive asteroids is limited by spatial resolution, which precludes tying spectral feature differences to particular phases and alteration histories. We use microimaging VSWIR spectroscopy of a suite of carbonaceous chondrites to characterize their observed spectral diversity and link these to the spectral diversity observed in primitive asteroids.

We imaged 24 carbonaceous chondrites with different degrees of aqueous alteration and thermal metamorphism with the Ultra-Compact Imaging Spectrometer (UCIS) over the 0.4 – 2.6µm wavelength range at a ~80µm/pixel spatial resolution.

We performed principal component analysis (PCA) using an adapted processing pipeline and eigenvectors from the expanded Bus-DeMeo asteroid taxonomy to observe the chondrites along the key axes of dataset variance among the classified asteroids. The top two principal components separate C-complex asteroids (from which carbonaceous chondrites are thought to originate) from rocky asteroids with strong absorption features at 2 μm, including S-complex and V-complex asteroids. The bulk, averaged spectra of a majority of the carbonaceous chondrites plot with the dark asteroid spectra, though not exclusively with C-complex asteroids. We also observe clustering of bulk chondrite spectra with D-class, K-class, and B-class asteroids.

Individual spectra from image cubes show a much wider spread along the two primary axes of variance than the asteroids, as expected for sub-mm scale imaging of heterogeneous chondrites. Examples of chondrite endmember clusters include spectra from CR2 chondrites with strong 0.95 and 1.95μm absorption features suggesting greater low-Ca pyroxene content. Spectra from CV3 chondrites also display a single broad absorption feature at ~1.9μm not observed for any asteroid classes. Second, we performed another PCA analysis using the axes of variance relevant to primitive asteroids. We will present an analysis of the VSWIR spectra of the endmember constituents and their distribution. Image cube data will also be used in conjunction with traditional petrologic approaches to identify the phases driving the observed spectral diversity.