Retrieving optical constants from laboratory spectra of carbonaceous chondrites: A step towards understanding the mineralogy of primitive asteroids

The advent of the James Webb Space Telescope (JWST) has enabled a paradigm shift in planetary science, offering unprecedented spectroscopic sensitivity and wavelength coverage that are unveiling the complex mineralogy of small bodies throughout the solar system. By transcending traditional taxonomic classifications, these observations expose subtle compositional nuances that push the limits of current spectral modeling frameworks. The spectral data of small bodies obtained by the JWST has highlighted a critical bottleneck: the requirement for expanded laboratory reference libraries and experimental datasets of materials subjected to the unique thermal and radiative conditions of space.

Central to this challenge is the interpretation of phyllosilicates on asteroidal surfaces. These materials are key products of aqueous alteration, and serve as diagnostic indicators of a body's thermal and chemical evolution. The formation and crystalline structure of these minerals are highly sensitive to environmental stressors, resulting in profound spectral and structural divergences between terrestrial analogs and those formed in vacuum [1]. To bridge these modeling gaps, this study implements a robust inversion technique to retrieve reliable optical constants (n and k) from carbonaceous chondrite meteorites, by employing an inversion technique based on the Hapke radiative transfer model [2], and adapted from the framework by Davalos et al. (2016) [3]. These refined optical inputs will provide a more rigorous foundation for interpreting JWST data of asteroids compositions and constraining the evolutionary history of the solar system’s most primitive bodies.

References

• Aqueous alteration on asteroids: Linking the mineralogy and spectroscopy of CM and CI chondrites. McAdam, M. et al. Icarus 2015. 
• Theory of Reflectance and Emittance Spectroscopy. Bruce Hapke. Cambridge University Press. OCLC: 775869853. eISBN: 9781139025683. 2012
• Numerical determination of visible/NIR optical constants from laboratory spectra of HED meteorites. Davalos, J. A. et al. Icarus. 2016.