Compositional variations in sands of the Bagnold Dunes, Gale crater, Mars, from visible‐shortwave infrared spectroscopy and comparison with ground truth from the Curiosity rover

Lapôtre, M. G. A.; Ehlmann, B. L.; Minson, S. E.; Arvidson, R. E.; Ayoub, F.; Fraeman, Abigail A.; Ewing, R. C.; Bridges, N. T.

doi:10.1002/2016je005133

Cited by 70 publications

(87 citation statements)

References 77 publications

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“…This is consistent with work in the greater Gale region where olivine is the dominant mafic signature with pyroxene accompanying it in some but not all CRISM scenes [Ehlmann and Buz, 2015]. An exception to the lack of pyroxene is within sand dunes on the Gale crater floor, where pyroxene absorptions are variably strong, consistent with previous studies [Lane and Christensen, 2013;Seelos et al, 2014;Lapotre et al, 2017]; however, we do not focus on the dunes in this study.…”

Section: Mineral Detections 411 Crismsupporting

confidence: 92%

Mineralogy and stratigraphy of the Gale crater rim, wall, and floor units

et al. 2017

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The Curiosity rover has detected diverse lithologies in float rocks and sedimentary units on the Gale crater floor, interpreted to have been transported from the rim. To understand their provenance, we examine the mineralogy and geology of Gale's rim, walls, and floor, using high‐resolution imagery and infrared spectra. While no significant differences in bedrock spectral properties were observed within most Thermal Emission Imaging System and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) scenes, some CRISM scenes of rim and wall rocks showed olivine‐bearing bedrock accompanied by Fe/Mg phyllosilicates. Hydrated materials with 2.48 μm absorptions in Gale's eastern walls are spectrally similar to the sulfate unit in Mount Sharp (Aeolis Mons). Sedimentary strata on the Gale floor southwest of the landing site, likely coeval with the Bradbury units explored by Curiosity, also are hydrated and/or have Fe/Mg phyllosilicates. Spectral properties of these phyllosilicates differ from the Al‐substituted nontronite detected by CRISM in Mount Sharp, suggesting formation by fluids of different composition. Geologic mapping of the crater floor shows that the hydrated or hydroxylated materials are typically overlain by spectrally undistinctive, erosionally resistant, cliff‐forming units. Additionally, a 4 km impact crater exposes >250 m of the Gale floor, including finely layered units. No basement rocks are exposed, thus indicating sedimentary deposits ≥250 m beneath strata studied by Curiosity. Collectively, the data indicate substantial sedimentary infill of Gale crater, including some materials derived from the crater rim. Lowermost thin layers are consistent with deposition in a lacustrine environment; interbedded hydrated/hydroxylated units may signify changing environmental conditions, perhaps in a drying or episodically dry lake bed.

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Section: Mineral Detections 411 Crismsupporting

confidence: 92%

Mineralogy and stratigraphy of the Gale crater rim, wall, and floor units

et al. 2017

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“…We also analyzed the NIR spectra of two dune fields within Gale crater (Figure 7). We found that the Bagnold dunes contain pyroxene with contributions from olivine, which is consistent with the results from Lapotre et al (2017) and Seelos et al (2014). The sand sea spectrum exhibits a 1-μm absorption band, which suggests that there is mafic mineralogy present.…”

Section: 1029/2018ea000380supporting

confidence: 89%

“…Therefore, we are interested in detangling the grain size and composition effects of the addition of dust versus grain-size sorting of sand-sized particles in sand dunes. Lapotre et al (2017) demonstrated that there is a measurable compositional difference within the Bagnold dunes, likely due to grain size sorting. When different sized sand grains have preferentially different compositions, then the sorting that occurs with saltation at dunes will not only sort the sand by grain size, but also by composition (e.g., Mangold et al, 2011).…”

Section: The Bagnold Dunes and The Western Sand Seamentioning

confidence: 99%

THEMIS‐VIS Investigations of Sand at Gale Crater

Bennett

Hill

Murray

et al. 2018

Earth and Space Science

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Gale crater is the landing site of the Mars Science Laboratory (MSL) rover, Curiosity. Here we present Thermal Emission Imaging System Visible Imaging Subsystem (THEMIS‐VIS) mosaics in gray scale and in false color of Gale crater. We use these data products, in addition to THEMIS thermal infrared decorrelation stretch (DCS) mosaics, thermal inertia derivations, and near‐infrared spectra to investigate the MSL traverse area and sand across Gale crater. We identified several THEMIS‐VIS color units in the MSL traverse area that may correlate to the amount of sand cover that is present on each unit. This suggests that THEMIS‐VIS color is extremely useful in identifying dark basaltic sand, which appears as blue in THEMIS‐VIS false color images. We test this hypothesis by identifying small (~several pixels) blue patches on the southeast side of the central mound in Gale crater and confirming that they are patches of sand in High Resolution Imaging Science Experiment (HiRISE) images. Sand dunes on the crater floor exhibit variations in all data sets utilized in this study, with the Bagnold dunes and the western sand sea exhibiting the most notable differences. We propose that these differences are the result of a thin layer of dust that covers the western sand sea, although we do not rule out possible effects from grain size sorting.

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“…Our model results show greater abundance errors than Mustard and Pieters [1987] for their mixtures because they constrain grain size while we do not. This emphasizes a key role that Journal of Geophysical Research: Planets 10.1002/2016JE005248 independent constraints on grain size-e.g., from thermal inertia [e.g., Liu et al, 2016] or from geologic context [e.g., Lapotre et al, 2017]-can have in effectively minimizing the errors in unmixing data. Altogether, our results highlight the importance of calculating uncertainties on unmixing model fits and considering the geological implications of the full range of permitted solutions, rather than interpretations relying on a sole acceptable solution.…”

Section: Discussionmentioning

confidence: 99%

“…Altogether, our results highlight the importance of calculating uncertainties on unmixing model fits and considering the geological implications of the full range of permitted solutions, rather than interpretations relying on a sole acceptable solution. Our overall recommendation is to report both the MAP and the full 95% confidence interval (or whatever confidence interval is desired) to properly acknowledge the relatively high uncertainties from spectral unmixing [e.g., Lapotre et al, 2017].…”

Section: Discussionmentioning

confidence: 99%

A probabilistic approach to remote compositional analysis of planetary surfaces

2017

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Reflected light from planetary surfaces provides information, including mineral/ice compositions and grain sizes, by study of albedo and absorption features as a function of wavelength. However, deconvolving the compositional signal in spectra is complicated by the nonuniqueness of the inverse problem. Trade‐offs between mineral abundances and grain sizes in setting reflectance, instrument noise, and systematic errors in the forward model are potential sources of uncertainty, which are often unquantified. Here we adopt a Bayesian implementation of the Hapke model to determine sets of acceptable‐fit mineral assemblages, as opposed to single best fit solutions. We quantify errors and uncertainties in mineral abundances and grain sizes that arise from instrument noise, compositional end members, optical constants, and systematic forward model errors for two suites of ternary mixtures (olivine‐enstatite‐anorthite and olivine‐nontronite‐basaltic glass) in a series of six experiments in the visible‐shortwave infrared (VSWIR) wavelength range. We show that grain sizes are generally poorly constrained from VSWIR spectroscopy. Abundance and grain size trade‐offs lead to typical abundance errors of ≤1 wt % (occasionally up to ~5 wt %), while ~3% noise in the data increases errors by up to ~2 wt %. Systematic errors further increase inaccuracies by a factor of 4. Finally, phases with low spectral contrast or inaccurate optical constants can further increase errors. Overall, typical errors in abundance are <10%, but sometimes significantly increase for specific mixtures, prone to abundance/grain‐size trade‐offs that lead to high unmixing uncertainties. These results highlight the need for probabilistic approaches to remote determination of planetary surface composition.

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Compositional variations in sands of the Bagnold Dunes, Gale crater, Mars, from visible‐shortwave infrared spectroscopy and comparison with ground truth from the Curiosity rover

Cited by 70 publications

References 77 publications

Mineralogy and stratigraphy of the Gale crater rim, wall, and floor units

Mineralogy and stratigraphy of the Gale crater rim, wall, and floor units

THEMIS‐VIS Investigations of Sand at Gale Crater

A probabilistic approach to remote compositional analysis of planetary surfaces

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