CARBONACEOUS CHONDRITES IN THE THERMAL INFRARED: WHAT WE MIGHT EXPECTTO SEE WITH THE OSIRIS-REX THERMAL EMISSION SPECTROMETER.
V. E. Hamilton, Southwest Research Institute, 1050 Walnut St. #300, Boulder, CO 80302 USA;hamilton@boulder.swri.edu.

Emissivity (1-R), offset

Introduction: The Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer(OSIRIS-REx) mission will arrive at the primitive, B-type (carbonaceous), asteroid Bennu in 2018 [1]. OSIRISREx is the first planetary mission to carry complementary visible to near infrared (VNIR) and thermal infrared(TIR) spectrometers, which will characterize the asteroid’s regolith composition. The OSIRIS-REx ThermalEmission Spectrometer (OTES) is a Michelson interferometer based on the heritage Mars Exploration Rovers
Miniature Thermal Emission Spectrometer (MER Mini-TES) design. OTES will characterize the thermophysicaland mineralogical properties of Bennu from 1820 – 200 cm-1 (5.5 - 50 µm). This presentation will review thethermal infrared spectroscopy of carbonaceous chondrites (CCs), present new measurements of individual phases in CCs, and discuss the spectral signatures OTES might find on the surface of Bennu.
Carbonaceous chondrites in the TIR: Suites of TIR carbonaceous chondrite bulk (whole rock) spectra generally have been measured in transmission [e.g., 3-4] and show, for example, that silicate-dominated spectralfeatures vary with petrologic type as the dominant mineralogy shifts from hydrous silicates in types 1-2 to anhydrous silicates in types >3.0. These data also have been used to document spectral differences between phyllosilicate-dominated bulk meteorite spectra and the spectra of terrestrial phyllosilicate phase separates [4-5]. Emission and reflectance data are more analogous to planetary surface spectra but have not been measured as commonly [e.g., 6]. Spectra of individual CC phases are rarer but are available from discrete microspectroscopic
measurements [e.g., 7]. Mapping microspectroscopy offers a means of obtaining both bulk meteorite spectra andphase-specific spectra and also allows for a detailed examination of the TIR properties of CC meteorites in petrologic context [e.g., 8]. In this presentation, I will show TIR reflectance spectra of carbonaceous chondritesrepresenting petrologic types 1 – 6 (e.g., Figure 1) as well as phase-specific spectra that can be compareddirectly to the spectra of mineral analogue separates and used for quantitative determination [9] of carbonaceouschondrite mineralogy from TIR spectra.
What OTES may see at Bennu: Comparison of Bennu telescopic spectra and carbonaceous meteorite spectra in the VNIR suggests that CI and CM meteorites (petrologic types 1 - 2) are the most likely analogues forBennu at those wavelengths [2]. TheWavelength (µm)
se meteorites contain anhydrous sili10121520 25cates, hydrated phyllosilicates, organics, magnetite, and sulfides. In thisAlais (CI1)case, OTES should see spectra dominated by these phases. Within these
LAP 02277 (CM1)two petrologic types, there is significant variability in bulk spectral character that is directly related to variaMurchison (CM2)tions in mineral proportions and solid
solution chemistry within and beMurray (CM2)tween different meteorite groups(e.g., Figure 1, top four spectra),which will enable us to further conALH A77307 (CO3.0)
strain the composition of the asteroid.
References: [1] Lauretta, D. S. et
ALH 83108 (CO3.5)
al. (2015) Meteorit. Planet. Sci., 50,834-849. [2] Clark, B. E. et al. (2011)
ALH 85002 (CK4)
Icarus, 216, 462-475. [3] Sandford, S.
A. (1984) Icarus, 60, 115-126. [4]Beck, P. et al. (2014) Icarus, 229,EET 90026 (CK5)263-277. [5] Beck, P. et al. (2010)
GCA, 74, 4881-4892. [6] Salisbury, J.
LEW 87009 (CK6)
W. et al. (1991) Icarus, 92, 280-297.
[7] Morlok, A. (2008) Meteorit. Plan1200
1000800600400
et. Sci., 43, 1147-1160. [8] Hamilton,
Wavenumber (cm-1)
V. E. and Connolly, H. J. (2012)
LPSC, 43, Abstract #2495. [9] Ramsey, M. R. and Christensen, P. R. Figure 1. TIR spectra of carbonaceous chondrites ranging from petrologic type 1 – 6 showing the range from aqueous alteration (phyllosili(1998) JGR, 103, 577-596.
cate-dominated) to thermal metamorphism (olivine-dominated).