Hydrothermal silica deposits on the surface of Mars with textures analogous to terrestrial hot spring deposits are, arguably, one of the best potential targets in the search for evidence of life beyond Earth. Here we investigate terrestrial hot spring digitate silica structures (modern: El Tatio, Chile; Mars Pool at Rotokawa geothermal area, and Te Kopia thermal stream, New Zealand; 1.6–1.8 ka: Opal Mound, Utah, U.S.A.), which are texturally and mineralogically analogous to martian deposits in the Columbia Hills of Gusev crater, in order to elucidate how their physical properties vary with depositional environment, and to help guide future remote sampling endeavors. Micro-computed tomography allows visualization of the internal texture of geological materials through variations in porosity and relative density, and is demonstrated here as a key, non-invasive technique for investigating future returned planetary samples. Bulk porosity, associated with pore sizes greater than >1–2 μm, varies from 4.7 to 21.3% in the four studied terrestrial digitate sinter samples, representing a range of fluid pHs of formation. Moreover, density variations between laminae largely reflect a nano-scale porosity (<1–2 μm) controlled by silicification of microbial material and/or recrystallization due to incipient diagenesis. Nano-indentation measurements of the digitate structures reveal variations in hardness and the reduced Young's modulus. The hardness of opal-A in modern digitate sinter varies, on average, from 2 to 4 GPa (El Tatio, Mars Pool, Te Kopia), but hardens with incipient diagenesis to >6 GPa (Opal Mound). Regions of nano-porous silica in all samples reduces the hardness in these areas to <1 GPa. No significant variation in material properties can be correlated to different fluid chemistries of the modern samples. Collectively, these results imply that the preservation of silicified microbes in digitate sinter structures should lead to a decrease in material hardness and elastic modulus owing to higher porosity in microbial laminae, whereas recrystallization of opal-A or secondary fluid precipitation will lead to hardening. For future remote sampling on Mars, the range of material properties of siliceous materials must be considered when designing appropriate sampling devices, as martian materials both harder and softer than accounted for in the design process may create sampling challenges.

These files were produced as part of the study entitled “Thermal infrared spectral characteristics of Martian dust deposits and evidence for atmosphere-regolith interactions”, published in Icarus. If you use the data, please kindly cite our paper: Rogers, A. D., S. W. Ruff, and M. D. Smith (2023), Thermal infrared spectral characteristics of Martian dust deposits and evidence for atmosphere-regolith interactions, Icarus, doi: https://doi.org/10.1016/j.icarus.2023.115687 Files contained in this archive: MAPS -- all are 4 pixels per degree, centered at 0 deg longitude and latitude (-180 to 180 E, -90 to 90N) surface_spectral_emissivity.tif -- the global surface emissivity data set (GeoTIFF), 106 bands surface_spectral_emissivity_noiserem.tif -- the global surface emissivity data set, 106 bands, noise removed (GeoTIFF) DCI.tif -- DCI map (GeoTIFF) surf_emiss_9um.tif -- the 9 micron emissivity map (GeoTIFF) surf_emiss_32um.tif -- the 32 micron emissivity map (GeoTIFF) SAM_maskedDCI96.tif -- the 1-SAM map (GeoTIFF) tes1630map.tif -- the 1630cm-1 map (GeoTIFF) tesCFmap.tif -- the CF map (GeoTIFF) tesCFmapchi.tif -- the chi-squared error map to the parabolic fit for CF (GeoTIFF) broadband_emissivity_150K.tif -- broadband emissivity at 150K broadband_emissivity_220K.tif -- broadband emissivity at 220K broadband_emissivity_300K.tif -- broadband emissivity at 300K mask_DCI_96.tif -- all pixels with DCI <0.96 (GeoTIFF) null_data_mask.tif -- all pixels with data (GeoTIFF) ENVI ROI files DCI_bins.roi -- ENVI ROI files for the DCI bins used to calculate spectral averages in Fig. 6a-b SAM_rois.roi -- ENVI ROI files for the 21 locations shown in Fig S2 SPECTRA DCI_bin_means.txt -- spectra shown in Fig 6a DCI_bin_means_noiserem.txt -- spectra shown in Fig 6b sam_roi_means_noiserem.txt -- spectra shown in Fig 9a OTHER emissivity_xaxis -- wavenumber values for surface emissivity data set and spectra

Regional to micron-scale controls on preservation of biosignatures in Phanerozoic hot spring microbial sinter KATHLEEN A CAMPBELL1, DIEGO GUIDO2, AYRTON HAMILTON1, MICHAEL ROWE1, BARBARA LYON1, DR. BONNIE TEECE3, FREDERIC FOUCHER4, FRANCES WESTALL5, STEVE RUFF6 AND MARTIN J. VAN KRANENDONK7 1The University of Auckland 2Universidad Nacional de La Plata 3University of New South Wales 4Centre National de la Recherche Scientifique 5Centre de Biophysique Moléculaire, CNRS 6Arizona State University 7Australian Centre for Astrobiology, University of New South Wales Presenting Author: ka.campbell@auckland.ac.nz

Exposures of bedrock rich in olivine and carbonate link Gusev crater and the Nili Fossae region (NFR), both of which have the highest abundance of olivine yet identified on Mars. They are recognized as possible explosive volcanic tephra deposits, but the nature of their eruption and emplacement is poorly constrained, limiting understanding of what may be a widespread volcanic process on early Mars. The compositional and morphologic similarities of these widely separated olivine and carbonate-rich rocks have not been investigated previously. We examined orbital and in situ thermal infrared spectra and find notably similar compositions between the two locations, with olivine ranging from ~Fo53 to Fo75 and carbonates composed of multiple Mg and Fe-rich phases, although with minimal magnesite in the NFR. A range of morphologic and textural features occur in the deposits of explosive volcanism on Earth that can be used to constrain the origin of those on Mars. We observed features of the olivine-rich bedrock in both locations that resemble those of welded ignimbrite deposits on Earth that formed from pyroclastic density currents in cataclysmic explosive volcanic eruptions. If correct, an ignimbrite interpretation for the olivine-rich bedrock in the NFR and Gusev crater may apply to other occurrences on Mars and indicate a style of volcanism more common in its early history.

Abstract Dust makes the red planet red. Without dust, Mars would appear mostly as shades of gray. The reddish hue arises from a small amount of oxidized iron among its basaltic mineral constituents. In this sense, Mars is a rusty world. Martian dust is a ubiquitous material of remarkably uniform composition that spans the globe, filling the skies and covering the land in a temporally and spatially varying manner. It is routinely lifted into the atmosphere via convective vortices known as dust devils. Dust in the atmosphere waxes and wanes according to season. Every few Martian years, the planet is fully encircled in atmospheric dust of sufficient opacity that its surface markings and landforms are completely obscured from view of Earth-bound telescopes and Mars-orbiting satellites. Such global dust events last for weeks or months, long enough to jeopardize solar-powered spacecraft on the surface. Dust particles suspended in the thin Martian atmosphere ultimately fall to the surface, completing the cycle and contributing to a range of features that are still being discovered and investigated.

The purpose of this white paper is to document the need to continue our search for ancient life on Mars.Upcoming missions are taking the first steps by directly seeking signs of ancient life with in situ exploration (Mars 2020 and ExoMars) and Mars Sample Return (MSR).However, these missions will not explore the full suite of habitable paleoenvironments on Mars and only a limited geographic region.Whereas a positive result would be a watershed moment for humanity and would compel us to explore the full extent of Mars' biosphere, a negative result would not indicate life never existed on Mars, and additional investigations will be needed.So in either case, as we go forward into the next decade, we will need to target a broader range and distribution of habitable paleoenvironments on Mars, constrain the history of water on Mars, and define a more complete catalog of possible biosignatures, as well as their ubiquity and stability under Mars' preservational conditions.This will also require instrumentation developments that could improve the detection of ancient biosignatures during future robotic and human missions.

As the new decade begins, new programmatic strategies to conduct more frequent, lower cost missions are beginning to be applied to deep space robotic science missions, such as the Commercial Lunar Payload Services (CLPS) program. These new strategies include moving from cost-plus contracts towards fixed price contracts, commercial contractors increasingly sharing in development costs, finding launch opportunities through ride sharing and comanifesting payloads, and making use of smallsats and other spacecraft with off-the-shelf hardware. While these new practices are now being applied in many areas across NASA, they are not yet being widely implemented in the Mars exploration program, where large bespoke missions have become the dominant programmatic strategy. As the decadal survey for planetary science in the 2020’s begins its deliberations, it should consider how programmatic strategies that emphasize lower cost, more frequent missions to Mars can provide groundbreaking science return and enable the beginning of a new age in Martian exploration

Whitepaper submitted to the Planetary Science and Astrobiology Decadal Survey 2023-2032. Additional co-authors: Sara Motaghian, Brandi L. Carrier, William H. Farrand, Marc D. Fries, Peter Grindrod, Andrew Langedam, Jeremie Lasue .

Summary The search for life on Mars has been guided in part by the search for biosignatures in Martian analogues on Earth. Siliceous hot springs are key astrobiological targets as they provide ideal conditions for biogenesis. This work documents biomarker analyses carried out on siliceous hot spring sinters from El Tatio, Chile, and from the Taupo Volcanic Zone, New Zealand, with an age range from actively forming to fossil deposits (∼1–21 ka). In addition, older samples (Pliocene–Miocene) were analysed from the Coromandel Volcanic Zone, New Zealand. Some of the data have already been published. The key hydrocarbons detected in some (or all) of the samples include n-alkanes, isoprenoids, monomethylalkanes, tricyclic and tetracyclic terpanes, hopanes, 2α-methylhopanes, steranes, and some aromatic hydrocarbons. A series of biomarker and aromatic hydrocarbon maturity parameters suggest that most samples have entered the oil generation window, and that maturity is strongly variable between samples and by parameter. These signals are indicative of organic matter sourced from subsurface hydrothermal fluids migrating from deeper immature source rocks that have been hydrothermally altered, rather than from the in situ material preserved within the samples in the hot spring environment.

Spectra from the Mars Global Surveyor Thermal Emission Spectrometer (TES) display a combination of features attributable to surface and atmospheric components. In order to fully recognize and interpret surface spectral features, the atmospheric spectral features must be removed through some form of surface-atmosphere separation (SAS). Multiple SAS techniques are available representing a range of complexity and accuracy. A ratio between spectra from a region of interest and a relatively spectrally bland, dusty location is an effective SAS technique, but the resulting ratio spectrum contains spectral features of surface dust (SD) from the dusty location. We exploit the uniform spectral character of SD across Mars to produce dust-removed ratio spectra (DRRS). This simple and robust technique allows TES spectra to be compared directly to laboratory spectra and to Miniature-TES spectra from the Mars Exploration Rovers. Although previous SAS techniques yield atmospherically corrected spectra that can serve this purpose, they are more challenging to implement, retain fewer data points, and are less accurate in some cases. The DRRS technique provides an option that is well suited to both quick-look assessments of TES spectra and in-depth analyses using follow-on spectral modeling techniques. We show that DRRS of olivine-rich bedrock in the Nili Fossae region display spectral features that match olivine with a composition ranging from similar to Fo50 to <Fo90 and that match olivine-rich Algonquin-class rocks in the Columbia Hills of Gusev crater.

The origin and age of opaline silica deposits discovered by the Spirit rover adjacent to the Home Plate feature in the Columbia Hills of Gusev crater remains debated, in part because of their proximity to sulfur-rich soils. Processes related to fumarolic activity and to hot springs and/or geysers are the leading candidates. Both processes are known to produce opaline silica on Earth, but with differences in composition, morphology, texture, and stratigraphy. Here, we incorporate new and existing observations of the Home Plate region with observations from field and laboratory work to address the competing hypotheses. The results, which include new evidence for a hot spring vent mound, demonstrate that a volcanic hydrothermal system manifesting both hot spring/geyser and fumarolic activity best explains the opaline silica rocks and proximal S-rich materials, respectively. The opaline silica rocks most likely are sinter deposits derived from hot spring activity. Stratigraphic evidence indicates that their deposition occurred before the emplacement of the volcaniclastic deposits comprising Home Plate and nearby ridges. Because sinter deposits throughout geologic history on Earth preserve evidence for microbial life, they are a key target in the search for ancient life on Mars.

Digitate siliceous hot spring deposits are a form of biomediated sinter that is relatively common in the Taupo Volcanic Zone (TVZ), New Zealand, and elsewhere on Earth. Such deposits have gained prominence recently because of their morphological similarity to opaline silica rocks of likely hot spring origin found by the Spirit rover on Mars and the consequent implications for potential biosignatures there. Here, we investigate the possible relationship between microbial community composition and morphological diversity among digitate structures from actively forming siliceous hot spring sinters depositing subaerially in shallow discharge channels and around pool rims at several physicochemically distinct geothermal fields in the TVZ. The TVZ digitate sinters range in morphologic subtype from knobby to spicular, and are shown to be microstromatolites that grow under varied pH ranges, temperatures, and water chemistries. Scanning electron microscopy and molecular analyses revealed that TVZ digitate sinters are intimately associated with a diverse array of bacterial, archaeal and eukaryotic micro-organisms, and for most digitate structures the diversity and quantity of prokaryotes was higher than that of eukaryotes. However, microbial community composition was not correlated with morphologic subtypes of digitate sinter, and observations provided limited evidence that pH (acidic versus alkali) affects morphology. Instead, results suggest hydrodynamics may be an important factor influencing variations in morphology, while water chemistry, pH, and temperature are strong drivers of microbial composition and diversity.

A Miniature Thermal Emission Spectrometer (Mini-TES), based on a Michelson interferometer and Cassegrain telescope, was carried by the Spirit rover in Gusev crater and Opportunity rover at Meridiani Planum to determine the bulk mineralogy of surface materials. Spectra from the plains of Gusev demonstrate the ubiquity of olivine-rich basaltic rocks, with additional examples lofted into the adjacent Columbia Hills by meteoroid impacts. Hundreds of rocks observed with mini-TES in the Columbia Hills display spectral characteristics of variable alteration intensity, but likely with very little water involved. Rare exceptions include a tephra deposit cemented by Mg–Fe carbonates and nodular opaline silica rocks, likely indicative of a hot spring/geyser environment. Opportunity’s mini-TES confirmed orbital identification of crystalline hematite at Meridiani Planum and spectral characteristics indicative of a transition from a precursor goethite phase. The sedimentary bedrock that hosts the hematite has spectral features consistent with Al-rich opaline silica, Mg-, Ca-, and Fe-bearing sulfates, plagioclase feldspar, and nontronite. Rare rocks at both sites are recognizable as iron meteorites from their infrared reflective properties.