Mid-infrared (5-25 μm) reflectance spectroscopy of carbonaceous meteorites and minerals at cryogenic temperatures in support of remote sensing data interpretation

Temperature effects on spectral properties of minerals and meteorites such as the peak position, band area and shape, were advanced decades ago (Singer & Roush, 1985). Few studies were performed analyzing the effects of space environment, such as low pressure and different temperature, on spectroscopic features. Most of these experiments were focusing on near infrared spectral region (Moroz, et al. 2000; Hinrichs & Lucey 2002; De Angelis, et al. 2019). Beyond 5 µm, the mid-infrared region is almost completely uncovered by temperature-dependent laboratory measurements. Thus, it is important to acquire spectra in vacuum at various temperatures and varying the particle sizes in this spectroscopic range for better simulating space environmental conditions. Ultimately, the interpretation of spectroscopic data from remote sensing of planetary surfaces will certainly be strengthened.

The experimental apparatus at INAF-Astrophysical Observatory of Arcetri allows reflectance measurements in an extended spectral range from VIS to far IR and at temperatures ranging from 65 K to 1000 K. Our presentation will cover a detailed analysis on temperature-dependent variation on mineral and carbonaceous chondrite samples in the spectral range 1500-400 cm^-1 (6.6-25 µm in wavelength) at cryogenic temperatures from 65 K to 350 K. Several mineral phases and meteorites are analyzed such as: pyroxene, olivine, serpentine, Tagish Lake (CI2-ungrouped), Aguas Zarcas (CM2) and Orgueil (CI1). Samples are prepared with grain sizes <20 μm, <200 μm, and 200-500 μm. Our experimental results show that temperature induces spectral features modifications such as peak position shifts, band area and peak intensity changes (Fig 1). All the modifications are reversible with temperature and the trend of variation is related to the sample composition and hydration level. Moreover, magnitude of temperature-dependent spectroscopic changes is strongly linked with grain size and composition. Clearly this type of analysis is pivotal for a correct interpretation of data collected by space telescopes and orbital spacecrafts.

Acknowledgement: This work is supported by the Italian Space Agency, grant ASI/INAF n.2017-37-H.0

1: De Angelis, S., et al. 2019. Icarus, 317, 388-411 ; 2: Hinrichs, J. L. & Lucey, P. G., 2002. Icarus, 155, 169-180 ; 3: Moroz, L., Schade, U. & Wash, R., 2000. Icarus, 147, 79-93 ; 4: Singer, R. B. & Roush, T. L., 1985. Journal of Geophysical Research, 90 (B14), 12434-12444