Through the Basaltic Looking Glass : Paired Remote Sensing and Experimental Studies of Glass on Mars

Introduction: Glasses on Mars, formed by impact melting and volcanism, likely make up a significant fraction of the regolith because they accumulate over time and there have been few processes operating in the last ~3.5 Ga to destroy them [1]. These glasses have exciting astrobiological implications because they can host microbial colonies and preserve biosignatures [2-5]; they may have also served as precursor phases for observed alteration minerals [6,7], and they are important to consider for astronaut safety [8]. However, glass has not been widely detected on the surface with remote sensing studies [9]. Here we report on two related efforts: (1) detecting glasses at multiple spatial scales on Mars by modeling remotely sensed data and (2) enhancing these models with synthetic martian glasses. Synthetic glasses: We are synthesizing four glass compositions relevant for the majority of volcanic and impact products on Mars (Fig. 1): (1) “ALK”: Alkaline basalt based on Curiosity measurements [10]; (2) “BLK”: Northwest Africa (NWA) 7034/7533, similar to the estimated bulk crustal composition [11,12]; (3) “VUL”: Adirondack-class basalt, believed to be representative of Noachian-Hesperian effusive volcanism [13]; (4) “OPS”: Representative of olivine-phyric shergottites, the most common martian meteorite type. We do not include high-Si glass (i.e., obsidian) or other terrestrial compositions because there is no evidence these are relevant for Mars. All compositions are synthesized at five fO2 conditions from QFM-2 to QFM+2 in 1-log unit steps, spanning the range of estimated martian conditions (reduced lavas to oxidized regolith). Varying fO2 is important because it is known to shift Fe2+ crystal field absorption positions by hundreds of nanometers in lunar glass analogs [14], and its effects at mid-infrared wavelengths remain unexplored. All 20 glasses will be measured with: (1) Visible/near-infrared (VNIR) spectroscopy using the custom-built UV-VIS-NIR spectrometer at RELAB; (2) The Asteroid and Lunar Environment Chamber at RELAB to measure true emissivity; (3) Mössbauer spectroscopy to quantify Fe3+/FeT ratios; (4) Electron probe microanalysis to verify major element compositions; (5) X-ray diffraction to ensure crystal-free glasses. Remote sensing: The spectra from these synthetic glasses will feed into our spectral mixture models used previously to identify glass-rich proximal impactites on crater central peaks [15]. This will enhance the sensitivity of these models to identify glass by including glasses of multiple compositions with ranges in Fe3+/FeT, instead of a single “glass” endmember that may not represent the glasses present on the surface.