Low-phase spectral reflectance and equivalent “geometric albedo” of meteorites powders

Beck, P.; Schmitt, B.; Potin, S.; Pommerol, A.; Brissaud, O. (2021). Low-phase spectral reflectance and equivalent “geometric albedo” of meteorites powders. Icarus, 354, p. 114066. Elsevier 10.1016/j.icarus.2020.114066

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Generally, the reflectance of a particulate surface depends on the phase angle at which it is observed. This is true for laboratory measurements on powders of natural materials as well as remote observations of Solar System surfaces. Here, we measured the dependences of reflectance spectra with phase angles, of a suite of 72 meteorites in the 400–2600 nm range. The 10–30◦phase angle range is investigated in order to study the contribution of Shadow Hiding Opposition Effect (SHOE) to the phase behavior. The behavior is then extrapolated to phase angle of 0◦using a polynomial fit, in order to provide grounds for comparison across meteorite groups (enabling to remove the contribution of shadows to reflectance) as well as to provide “equivalent albedo” values that should be comparable to geometric albedo values derived for small bodies. We find a general behavior of increasing strength of the SHOE with lower reflectance values (whether between samples or for a given samples with ab-sorption features). This trend provides a first order way to correct any reflectance spectra of meteorite powders measured under standard conditions (g =30◦) from the contribution of shadows. The g =0◦calculated reflectance and equivalent albedos are then compared to typical values of albedos for main-belt asteroids. This reveals that among carbonaceous chondrites only Tagish Lake group, CI, and CM chondrites have equivalent albedo compatible with C- and D-type asteroids. On the other hand equivalent albedo derived with CO, CR and CK chondrites are compatible with L- and K-type asteroids. The equivalent albedo derived for ordinary chon-drites is related to petrographic types, with low-grade petrographic type (type 3.6 and less) being generally darker that higher petrographic types. This works provides a framework for further understanding of the as-teroids meteorite linkage in particular when combining with colors and spectroscopy.

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