Emissivity and reflectance measurements for a suite of asteroid analogues in the 1 to 100 µm spectral range

Abstract

We have measured the emissivity and reflectance spectra for a suite of analogues of relevance for asteroid studies. The suite consists of ten samples - 3 meteorites and 7 synthetic or terrestrial analogue materials. Meteorite Allende represents the CV group of the Carbonaceous Chondrites meteorites; Murchison meteorite is representing the CM group, while the meteorite Millbillillie represents achondritic eucrites. Synthetic and terrestrial enstatite, synthetic L-Chondrite and H-Chondrite, graphite and two phyllosilicates (montmorillonite and serpentine) complete the set of analogues. In the Planetary Emissivity Laboratory (PEL) at the Institute for Planetary Research of the German Aerospace Center (DLR) in Berlin, we can measure bi-directional reflectance of samples in the whole 1 to 100 µm spectral range, by using an evacuated (10-4 bar) Bruker Vertex 80V FTIR spectrometer and a Bruker A513 reflection unit, allowing phase angles between 26° and 170°. The same instrument, coupled with an external emissivity chamber, can be used to measure emissivity of samples under the same vacuum and in the same wide spectral range, for sample temperatures from low (50° C) to very high (above 500° C). Complementary purged Bruker IFS88 FTIR spectrometer equipped with a Harrick SeagullTM bi-conical reflection unit permits to cover the 0.4 to 1.1 µm spectral range. For this study, when possible we measured the smaller available grain size separate (0-25 µm) and for emissivity measurements we kept the sample temperature to the minimum we could get. Our results can be important in support for future (sample return) missions to asteroids (i.e. Hayabusa II, MarcoPolo-R and OSIRIS-REx) as well as for the interpretation of ground based observations of asteroids and minor bodies.