Modal mineralogy of planetary surfaces from visible and near-infrared spectral data

Real planetary surfaces are composed of several to many different minerals and ices. Deconvolving a reflectance spectrum to material abundance in an unambiguous way is difficult, because the spectra are complex nonlinear functions of grain size, abundance, and material opacity. Multiple scattering models can provide approximate solutions to the radiative transfer in a particulate medium. The paper examines the different approaches which deal with the theory of radiative transfer on atmosphereless bodies. We present the relative merits of two scattering theories based on the equivalent slab model: the extensively used Hapke theory [1] and the Shkuratov theory [2]. The performances of the two models for determining mineral abundance in multicomponent mixtures are also evaluated using laboratory data. Finally, one application on real planetary surfaces will be shown

Mineralogy and Surface Composition of Asteroids

Methods to constrain the surface mineralogy of asteroids have seen considerable development during the last decade with advancement in laboratory spectral calibrations and validation of our interpretive methodologies by spacecraft rendezvous missions. This has enabled the accurate identification of several meteorite parent bodies in the main asteroid belt and helped constrain the mineral chemistries and abundances in ordinary chondrites and basaltic achondrites. With better quantification of spectral effects due to temperature, phase angle, and grain size, systematic discrepancies due to non-compositional factors can now be virtually eliminated for mafic silicate-bearing asteroids. Interpretation of spectrally featureless asteroids remains a challenge. This paper presents a review of all mineralogical interpretive tools currently in use and outlines procedures for their application.Comment: Chapter to appear in the Space Science Series Book: Asteroids IV, 51 pages, 7 figures, 2 table

Reflectance spectroscopy in planetary science: Review and strategy for the future

Reflectance spectroscopy is a remote sensing technique used to study the surfaces and atmospheres of solar system bodies. It provides first-order information on the presence and amounts of certain ions, molecules, and minerals on a surface or in an atmosphere. Reflectance spectroscopy has become one of the most important investigations conducted on most current and planned NASA Solar System Exploration Program space missions. This book reviews the field of reflectance spectroscopy, including information on the scientific technique, contributions, present conditions, and future directions and needs

Integrating Analytical and Remote Sensing Techniques to Investigate the Petrology of Planetary Surfaces

abstract: Interpreting the petrogenesis of materials exposed on the surface of planets and asteroids is fundamental to understanding the origins and evolution of the inner Solar System. Temperature, pressure, fO2, and bulk composition directly influence the petrogenetic history of planetary surfaces and constraining these variables with remote sensing techniques is challenging. The integration of remote sensing data with analytical investigations of natural samples, lab-based spectroscopy, and thermodynamic modelling improves our ability to interpret the petrogenesis of planetary materials. A suite of naturally heated carbonaceous chondrite material was studied with lab-based spectroscopic techniques, including visible near-infrared and Fourier transform infrared reflectance spectroscopy. Distinct mineralogic, and thus spectroscopic, trends are observed with increasing degree of thermal metamorphism. Characterization of these spectral trends yields a set of mappable parameters that will be applied to remotely sensed data from the OSIRIS-REx science payload. Information about the thermal history of the surface of the asteroid Bennu will aid in the selection of a sampling site, ensuring OSIRIS-REx collects a pristine regolith sample that has not experienced devolatilization of primitive organics or dehydration of phyllosilicates. The evolution of mafic magma results in distinct major element chemical trends. Mineral assemblages present in evolved volcanic rocks are indicators of these processes. Using laboratory spectroscopic analyses of a suite of evolved volcanic rocks from the Snake River Plain, Idaho, I show that these evolutionary trends are reflected in the spectral signatures of ferromagenesian and feldspar minerals. The Athena science package on the Mars Exploration Rover Spirit allows for the in situ investigation of bulk chemistry, texture, and mineralogy on the surface of Mars. Using the bulk composition of the Irvine and Backstay volcanic rocks, thermodynamic modeling was performed to further constrain the formation conditions of Martian volcanics. Irvine and Backstay compositions exhibit dramatic variations in modal mineralogy with changing fO2. Using these results, I show that the observed Mini-TES spectra of Irvine and Backstay can be adequately reproduced, and additional constraints can be placed on their primary fO2.Dissertation/ThesisDoctoral Dissertation Geological Sciences 201

Compositional Diversity Among Primitive Asteroids

Spectroscopic observations from the ultraviolet to the mid-infrared have revealed new and diagnostic differences among primitive asteroids. We review the spectral characteristics of these asteroids and their inferred compositional and physical properties. Primitive asteroids throughout the belt show carbon-rich compounds, varying degrees of aqueous alteration and even surface ice; recent observations provide significant new constraints on composition, thermal inertia, and other surface properties. New mid-infrared connections between primitive asteroids and interplanetary dust particles indicate that the latter sample a larger fraction of main belt asteroids than meteorites. Links with the composition of comets are consistent with a proposed continuum between primitive asteroids and comets. Two sample-return missions, OSIRIS-REx and Hayabusa 2, will visit primitive near-Earth asteroids (NEAs). Most spacecraft-accessible NEAs originate in the inner asteroid belt, which contains several primitive asteroid families and a background of primitive asteroids outside these families. Initial results from these families offer a tantalizing preview of the properties expected in the NEAs they produce. So far, primitive asteroids in the inner belt fall into two spectral groups. The first group includes the Polana-Eulalia families, which show considerable spectral homogeneity in spite of their dynamical and collisional complexity. In contrast, the Erigone and Sulamitis families are spectrally diverse and most of their members show clear 0.7 microns hydration features. The two sample-return targets (101955) Bennu and (162173) Ryugu, most likely originated in the Polana family.Comment: 31 pages, 11 figures, chapter 5 in Primitive Meteorites and Asteroids, Physical, Chemical, and Spectroscopic Observations Paving the Way to Exploratio

Astronomical Observations of Volatiles on Asteroids

We have long known that water and hydroxyl are important components in meteorites and asteroids. However, in the time since the publication of Asteroids III, evolution of astronomical instrumentation, laboratory capabilities, and theoretical models have led to great advances in our understanding of H2O/OH on small bodies, and spacecraft observations of the Moon and Vesta have important implications for our interpretations of the asteroidal population. We begin this chapter with the importance of water/OH in asteroids, after which we will discuss their spectral features throughout the visible and near-infrared. We continue with an overview of the findings in meteorites and asteroids, closing with a discussion of future opportunities, the results from which we can anticipate finding in Asteroids V. Because this topic is of broad importance to asteroids, we also point to relevant in-depth discussions elsewhere in this volume.Comment: Chapter to appear in the (University of Arizona Press) Space Science Series Book: Asteroids I

Exploring Exogenic Sources for the Olivine on Asteroid (4) Vesta

The detection of olivine on Vesta is interesting because it may provide critical insights into planetary differentiation early in our Solar System's history. Ground-based and Hubble Space Telescope (HST) observations of asteroid (4) Vesta have suggested the presence of olivine on the surface. These observations were reinforced by the discovery of olivine-rich HED meteorites from Vesta in recent years. However, analysis of data from NASA's Dawn spacecraft has shown that this olivine-bearing unit is actually impact melt in the ejecta of Oppia crater. The lack of widespread mantle olivine, exposed during the formation of the 19 km deep Rheasilvia basin on Vesta's South Pole, further complicated this picture. Ammannito et al., (2013a) reported the discovery of local scale olivine-rich units in the form of excavated material from the mantle using the Visible and InfraRed spectrometer (VIR) on Dawn. Here we explore alternative sources for the olivine in the northern hemisphere of Vesta by reanalyzing the data from the VIR instrument using laboratory spectral measurements of meteorites. We suggest that these olivine exposures could be explained by the delivery of olivine-rich exogenic material. Based on our spectral band parameters analysis, the lack of correlation between the location of these olivine-rich terrains and possible mantle-excavating events, and supported by observations of HED meteorites, we propose that a probable source for olivine seen in the northern hemisphere are remnants of impactors made of olivine-rich meteorites. Best match suggests these units are HED material mixed with either ordinary chondrites, or with some olivine-dominated meteorites such as R-chondrites.Comment: 62 pages, 12 figures, 4 tables; Icarus, Available online 30 January 2015, ISSN 0019-1035, http://dx.doi.org/10.1016/j.icarus.2015.01.01

Mineralogy and IR spectroscopy of the Tagish Lake C2 chondrite and enstatite chondrites

Sample-correlated X-ray diffraction (XRD) and diffuse-reflectance Fourier- transform infrared (DRIFTS) spectra were collected for seven samples of the Tagish Lake C2 chondrite and thirteen enstatite chondrites. A reconnaissance of the Tagish Lake chondrite was carried out using micro-XRD, SEM-EDX and EPMA. Modal mineral abundances were obtained from XRD data via Rietveld refinement. Grain densities were calculated for each sample based on the modal abundances. DRIFTS spectra are analogous to remote-sensing emission IR spectra, facilitating comparison with astronomical observations. Tagish Lake was found to be more varied in major mineralogy than has previously been reported. In addition to the documented carbonate-rich and carbonate-poor lithologies, a magnetite- and- sulphide-rich lithology, and a carbonaterich, siderite-dominated lithology have been observed. Several Tagish Lake samples may contain extraterrestrial sulphates. Terrestrially altered enstatite chondrites may be analogous to the regolith of certain rare M- and E-type asteroids (“W-class”) which possess a spectral feature consistent with hydrated minerals

Distinguishing relative aqueous alteration and heating among CM chondrites with IR spectroscopy

Using infrared (IR) spectroscopy of thin sections, we characterize the relative degree of aqueous alteration and subsequent heating of a suite of CM chondrites to document spectral indicators of these processes that can contextualize observations of carbonaceous asteroids. We find that the progressive aqueous alteration of CMs manifests in two spectral regions. The low-wavenumber region (1200–400 cm−1; 8–25 μm) records the increasing proportion of Mg-Fe phyllosilicates relative to anhydrous silicates as aqueous alteration proceeds, with a highly correlated shift of the Christiansen feature (CF) to lower wavenumber and the Si-O bending band minimum to higher wavenumber, and an increase in depth of the Mg-OH band (~625 cm−1). The strongest correlation (R2 = 0.90) with petrologic subtype is the distance between the CF and Si-O stretching band minimum, which predicts the petrologic subtype of the sample to within 0.1. The high-wavenumber region (4000–2500 cm−1, ≤3.33 μm) probes the variation in abundance and composition of Mg-Fe serpentine and tochilinite among the altered CMs. All moderately to highly altered CMs (≤2.3) have an OH/H2O (‘3 μm’) band emission maximum of 3690 cm−1 (2.71 μm) indicative of Mg-bearing serpentine, and mildly aqueously altered CMs (≥ 2.5) have a wider band with a complex shape that results from contributions of Fe-bearing serpentine and tochilinite. Among weakly heated CMs (Stage II; 300–500 °C), the low-wavenumber region exhibits spectral features resulting from the dehydration and dehydroxylation of phyllosilicates that include broadening of the Si-O stretching band and a shift of its minimum to lower wavenumber, and the disappearance of the Mg-OH band. The location of the Si-O bending band minimum appears to be unaffected by mild heating. Extensively heated CMs (Stage III+; > 500 °C) have a low-wavenumber region dominated by the spectral features of secondary, Fe-bearing olivine and low-Ca pyroxene and thus are readily distinguished from unheated and mildly heated CMs. The OH/H2O band of all heated CMs is broad and rounded with an emission peak at lower wavenumbers (≤3636 cm−1; ≥2.75 μm) than in unheated CMs. However, spectral and petrographic evidence suggests that our heated CMs have been compromised by terrestrial rehydration. Our study confirms that thermal metamorphism effects are concentrated within the matrix and suggests that the matrix of the CM WIS 91600 had a CI-like mineralogy prior to heating