Comets and Asteroids

Comparative Mid-Infrared Spectroscopy of Dark, Primitive Asteroids: Does Shared Taxonomic Class Indicate Shared Silicate Composition?

By Keith Cowing
Status Report
May 1, 2024
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Comparative Mid-Infrared Spectroscopy of Dark, Primitive Asteroids: Does Shared Taxonomic Class Indicate Shared Silicate Composition?
Modeled mixtures of magnesium rich pyroxenes and olivines plotted alongside the spectrum of 267 Tirza and 1268 Libya. The addition of pyroxene to the olivine mixtures changes the behavior of the spectrum at long wavelengths, broadening this emission feature from the distinct emission peak(s) seen in the spectra of olivine and pyroxene alone. Spectral features of olivine are marked in light green and of pyroxenes are marked in dark purple to highlight commonalities with the asteroid spectra. The feature at 19.5 µm is common to both olivine and pyroxene. The spectrum of 267 Tirza in particular shows evidence of both olivine and pyroxene. All mixtures shown here contain both amorphous and crystalline silicates mixed in a 3:1 ratio, while the proportion of olivine and pyroxene is varied. The shaded grey box highlights the location of a known artefact in the SL Spitzer data (the SL teardrop). Spectra of crystalline silicates are sourced from Koike et al. (2003) and Chihara et al. (2002), spectra of amorphous silicates are derived from optical constants from J¨ager et al. (1994); Dorschner et al. (1995) and J¨ager et al. (2003) (see text for modeling details and silicate compositions). — astro-ph.EP

Primitive asteroids with low albedos and red slopes in the visible and near infrared (VNIR) are found in both the Main Belt and the Jupiter Trojan clouds.

In order to determine whether the VNIR spectral similarities of primitive Main Belt asteroids and Jupiter Trojans are reflective of a true compositional similarity, we compare the mid-infrared silicate emission features of Main Belt and Jupiter Trojan asteroids.

Using archival data from the Spitzer Space Telescope’s IRS spectrograph and observations from the Stratospheric Observatory for Infrared Astronomy’s (SOFIA) FORCAST instrument, we analyze the 5-40 micron spectra of thirteen primitive Main Belt asteroids and compare them to those of Jupiter Trojans in the literature.

We find that while many primitive asteroids in the Main Belt resemble their Trojan counterparts with strong spectral signatures of olivine-rich high-porosity silicate regoliths, we identify (368) Haidea as a spectrally distinctive asteroid that lacks strong evidence of olivine in its MIR spectrum. Differences in silicate compositions among D-type asteroids imply a diversity of origins for primitive asteroids.

Oriel A. Humes, Audrey C. Martin, Cristina A. Thomas, Joshua P. Emery

Comments: 22 Pages, 9 figures, draft version accepted for publication in PSJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2404.19388 [astro-ph.EP] (or arXiv:2404.19388v1 [astro-ph.EP] for this version)
Submission history
From: Oriel Humes
[v1] Tue, 30 Apr 2024 09:24:13 UTC (2,255 KB)
Astrobiology, astrochemistry, Astrogeology,

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻