Investigating C-complex asteroids in the mid-infrared with the Spitzer Heritage Archive

The study of primitive asteroid composition can give great insight to the origin and formation of the solar system as primitive asteroids are widely thought to have experienced little thermal processing. Despite visible/ near-infrared (VNIR) data being more abundant, certain features in the VNIR make the composition difficult to discern for asteroids, therefore pairing it with diagnostic mid-IR data allows us to learn more about any given object. Certain emission features such as the 10 µm plateau can indicate the presence and composition of silicates such as quartz and olivine. Driven by a desire to improve interpretations of future JWST asteroid data, we focus on investigating C-complex asteroids from archival Spitzer data. Following the works such as Humes et al. 2024, Martin et al. 2023a, Martin et al. 2023b, and Emery et al. 2006, we use Spitzer Heritage Archive mid-IR spectra taken with the infrared spectrograph to present new thermal emission spectra for 15 C-complex asteroids. These asteroids include 7 Iris, 12 Victoria, 24 Themis, 90 Antiope, 96 Aegle, 114 Kassandra, 130 Elektra, 234 Barbara, 261 Prymno, 334 Chicago, 379 Huenna, 433 Eros, 554 Peraga, 762 Pulcova, and 1373 Cincinnati. The spectra were created by reducing the data through the Spitzer IRS Custom Extraction Software (SPICE), fitting and scaling it using a polynomial fit, and finally running it through the Near Earth Asteroid Thermal Model (NEATM). The thermal model is used to convert the Spitzer spectral data into an emissivity spectrum. The shape of the 10 µm silicate emission feature was categorized using the methods of Martin et al. 2023 and values such as feature bounds, peak locations, and slopes were measured. Our findings clearly show the 10 µm silicate emission feature in many studied asteroids and our derived values agree, within error margins, with published diameters and band parameters. We compare the asteroids to carbonaceous chondrite meteorites within the ASTER spectral library (Baldridge et al. 2009) using a chi-squared goodness of fit test to observe similarities in overall spectra shape, physical properties, and predicted composition. We will discuss the band parameters as well as comparisons to the meteorites regarding possible compositions.