¹Estelle Déau, ¹Linda J. Spilker, ²Alberto Flandes
¹NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena 91109 CA United States
²Ciencias Espaciales, Instituto de Geofísica, Universidad Nacional Autónoma de México, México, D.F., C.P. 04510, México

We investigate connections between the opposition phase curves and the spectra from ultraviolet to near infrared wavelengths of stony meteorites. We use two datasets: the reflectance dataset of Capaccioni et al., 1990 (Icarus, 83, 325), which consists of optical phase curves (from 2 to 45°) of 17 stony meteorites (3 carbonaceous chondrites, 11 ordinary chondrites, and 3 achondrites), and the spectral dataset from the RELAB database consisting of near-ultraviolet to near-infrared spectra of the same meteorites. We re-analyzed the first dataset and fit it with two morphological models to derive the amplitude A, the angular width HWHM of the surge and the slope S of the linear part. Our re-analysis confirms that stony meteorites have a non-monotonic behavior of the surge amplitude with albedo, which is also observed in planetary surfaces (Déau et al. 2013, Icarus, 226, 1465), laboratory samples (Nelson et al., 2004, Proc. Lunar Sci. Conf. 35, p. 1089) and asteroids (Belskaya and Shevchenko, 2000, Icarus, 147, 94). We find a very strong correlation between the opposition effect morphological parameters and the slope of the spectra between 0.75 μm and 0.95 μm. In particular, we found that meteorites with a positive amplitude-albedo correlation have a positive spectral slope between 0.75 μm and 0.95 μm, while meteorites with a negative amplitude-albedo correlation have a negative spectral slope between 0.75 μm and 0.95 μm. We have ruled out the role of the meteorite samples’ macro-properties (grain size, porosity and macroscopic roughness) in the correlations found because these properties were constant during the preparation of the samples. If this hypothesis is correct, this implies that other properties like the composition or the micro-properties (grain inclusions, grain shape or microscopic roughness) could have a preponderant role in the non-monotonic behavior of the surge morphology with albedo at small and moderate phase angles. Further accurate characterization of carbonaceous chrondrites samples are necessary to draw conclusions about the role of the micro-properties.

Reference
Déau E, Spilker LJ, Flandes A (2016) Re-analysis of previous laboratory phase curves: 2. Connections between opposition effect morphology and spectral features of stony meteorites. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.01.035]
Copyright Elsevier

¹Jaesub Hong, ²Suzanne Romaine and The MiXO team
¹Harvard University, 60 Garden Street, Cambridge 02138, MA, USA
²Smithsonian Astrophysics Observatory, 60 Garden Street, Cambridge 02138, MA, USA

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
HongJ, Romaine S and The MiXO team (2016) Miniature lightweight X-ray optics (MiXO) for surface elemental composition mapping of asteroids and comets. Earth, Planets and Space 68:35
Link to Article [doi:10.1186/s40623-016-0409-1]

¹Serventi Giovanna, ²Carli Cristian, ¹Sgavetti Mariaamaria
¹Department of Physics and Earth Sciences, University of Parma, Italy
²IAPS-Inaf, Tor Vergata, Roma, Italy

Anorthositic rocks are widespread on the lunar surface and have probably been formed by flotation of PL over a magma ocean. A large portion of pristine rocks are characterized by a low Mg/(Mg+Fe) ratio, and have been classified as ferroan anorthosite, and recently, after observation from SELENE Spectral Profiler,pure anorthosites regions with more than 98% PL have been recognized.
In this paper we analyze a set of mixtures with PL content similar to the ferroan anorthosites and to the pure anorthosite regions, using the Origin Software and the Modified Gaussian Model.We consider three plagioclases with varying FeOwt% contents (PL1, PL2 and PL3)andthree mafic end-members (1)100% orthopyroxene, (2) 56% orthopyroxene and 44% clinopyroxene, and (3) 100% olivine (OL). The spectral parameters considered here are: band depth, band center, band width, c0 (the continuum intercept) and c1 (the continuum offset).
Here we have shown that in pyroxene (PX)-bearing mixtures, the PX is distinguishable even in mixtures with only 1% PX and that PX band at ca. 900 nm is always deeper than PL1 band while PL2 and PL3are deeperthan OPX 900 nm band from95, 96% PL. In OL-bearing mixtures, OL detection limit is 2% when mixed with PL1, and 3% and 4% if mixed with PL2 and PL3.
We also demonstrated how spectral parameters vary with PL%, and, generally, increasing the PL content: (1) 1250 nm band depth decreases when mixed with OL, while it deepens in mixtures with PX; (2) 1250 nm band centers generally move towards longer wavelength for PL1-bearing mixtures, while do not show significant variationsconsidering PL2/PL3-mixtures; (3)1250 nm band width of PL1 in E1 and E5-mixtures substantially widens while in other mixtures itonly slightly varies.
Here we also proposed an application to a real case, from Proclus crater, revealing how studying terrestrial analogues is fundamental to infer hypothesis on the mineralogical composition of a planetary surface, but also how the spectral convergence of spectra characterized by different compositions can led to misleading interpretations.

Reference
Giovanna S, Cristian C, Mariaamaria S (2016) Deconvolution of mixtures with high plagioclase content for the remote interpretation of lunar plagioclase-rich regions. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.01.020]
Copyright Elsevier