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Exploring the hypothesis that life is present on Mars today is key to informing planetary protection issues at a pivotal time, with the clock ticking to return pristine samples before humans irrevocably alter the environment.

The mineralogy of paleolake sediment strata at the high elevation (~4300 m) Lejía depression in the Altiplano region of Chile reflect evolution of the lake geochemistry over time. This mineralogical study is part of a larger project characterizing the geochemistry and biology of several samples from a paleo terrace of the Lejía lake region. Visible/near-infrared (VNIR) reflectance measurements of several samples reveal variations in gypsum, carbonate, clays, iron oxides/hydroxides, and halite with depth. The spectral features are also consistent with abundant allophane or related poorly crystalline clay phases. Mg-calcite, gypsum, and poorly crystalline clays dominate the surface materials, while each of these components varies with depth at our study site. Sediments at Gale crater on Mars also include abundant poorly crystalline phases, phyllosilicates, gypsum, halite, and iron oxides/hydroxides. Thus, characterizing the spectral properties of paleolake sediments from the Lejía region may help constrain the spectral signatures of Gale crater sediments and other sites measured from orbit. Study Site. The broader Altiplano region of Chile provides an analog for Mars due to its extremely dry and salty conditions and this study was carried out as part of the SETI Institute team’s NASA Astrobiology Institute project (Cabrol et al., 2017). The Lejía region differs from others in the Chlean Altiplano due to its higher pH environment and the presence of clay minerals and carbonates in addition to the ubiquitous gypsum and halite otherwise characteristic of the Atacama region. Laguna Lejía is a shallow, salty lake spanning ~1 km in a depression between Láscar and other volcanoes in northern Chile where a larger glacial lake (10-15 km across) once stood (Grosjean et al., 1995). This high altitude basin is battered by winds and receives only limited precipitation, mostly from melting snow and ice from the surrounding mountains. Despite limited water, high UV radiation, and cold temperatures, zooplankton communities are present at Laguna Lejía (Muñoz-Pedreros et al., 2013). Further, genome-resolved metagenomics investigations are currently being developed to characterize the communities of microorganisms and their metabolisms in the paleo sediments of the Lejía lake (Lezcano et al., in preparation). Samples. The paleolake sediments investigated here were collected in 2018 from the upper 1 m of a lake terrace (Figure 1) adjacent to the current Lejía lake. The samples were kept frozen until studied. Extensive analyses are underway including X-ray diffraction (XRD), major element analyses, δ13C and δ15N isotope analyses, metagenomics, and lipid analyses (Lezcano et al., in preparation). XRD analyses determined the presence of albite, anorthite, Mg-calcite, gypsum, halite, andesine, muscovite, and quartz in many of these samples. Aliquots of 6 samples collected from different horizons were thawed, then air dried in the lab, gently crushed and dry sieved to Spectroscopic Analyses. Reflectance spectra of bulk sample materials and size fractions from each strata were measured using a FieldSpecPro ASD spectrometer from 0.35-2.5 µm relative to Spectralon. Spectra in this range include bands and features due to phyllosilicates, sulfates, carbonates, hydrous phases, and Fe-bearing minerals (e.g., Bishop, 2019). Results. VNIR spectra of the Lejía samples (Figure 2) exhibit changes with depth (Figure 1). Samples L-1, L-3, L-5, and L-6 are brighter overall and have stronger bands near 1.4 and 1.9 µm due to bound or adsorbed H2O in the samples (Figure 2a). These broad bands are most consistent with poorly crystalline aluminosilicates similar to allophane or to halite (NaCl) (Figure 2b). Mg-calcite is also present in some samples and would contribute a band near 2.34 µm. Some samples also contain feldspar and quartz, which would increase the spectral brightness but do not have spectral features in this range. Samples L-2 and L-4 have darker spectra, stronger bands near 0.97 µm due to Fe-bearing phases, and weaker water bands. Sample L-2 has the strongest bands due to gypsum, which is consistent with the XRD results. Sample L-6 also has some features due to gypsum. Compositional changes with depth highlight episodic variations in inputs to the lake over time. VNIR spectra for multiple size fractions of samples L-2 and L-6 document increases in spectral brightness typical for smaller particles as expected (Figure 3). Other small changes in the spectral properties are due to compositional variations associated with particle size. The VNIR spectra of L-2 are dominated by gypsum features at 1.45, 1.49, 1.53, 1.76, 1.94, 2.22, and 2.26 µm, but the coarse-grained samples include shifts in the bands near 1.4 and 1.9 µm towards shorter wavelengths, which is more consistent with phyllosilicates or allophane. The VNIR spectra of L-6 exhibit more variations with particle size due to the heterogeneous nature of this sample. This VNIR spectroscopy study of paleolake samples from Lejía demonstrates detection of alteration minerals in these sediments that can be used for interpretation of the martian orbital spectra at Gale crater and related sites on Mars and subsequently for constraining the aqueous geochemical environment on Mars. References: Bishop, J. L. (2019) Visible and near-infrared reflectance spectroscopy of geologic materials. In: Remote Compositional Analysis: Techniques for Understanding Spectroscopy, Mineralogy, and Geochemistry of Planetary Surfaces. Cambridge University Press. 68-101. Cabrol, N. A. and the SETI NAI Team (2017) From habitability to habitat – The current knowledge leaps and gaps in the search for biosignatures on Mars. AbSciCon, Mesa, Arizona. Abstract #3033. Grosjean, M., Geyh, M. A., Messerli, B. & Schotterer, U. (1995) Late-glacial and early Holocene lake sediments, ground-water formation and climate in the Atacama Altiplano 22–24°S. J.Paleolimnology, 14, 241-252. Muñoz-Pedreros, A., De los Ríos, P. & Möller, P. (2013) Zooplankton in Laguna Lejía, a high-altitude Andean shallow lake of the Puna in northern Chile. Crustaceana, 86, 1634-1643. Murchie, S. L., et al. (2009) The Compact Reconnaissance Imaging Spectrometer for Mars investigation and data set from the Mars Reconnaissance Orbiter's primary science phase. JGR, 114, E00D07.

Thermal response of the surface to solar insolation is a function of the topography and the thermal physical characteristics of the landscape, which include bulk density, heat capacity, thermal conductivity and surface albedo and emissivity. Thermal imaging is routinely used to constrain thermal physical properties by characterizing or modeling changes in the diurnal temperature profiles. Images need to be acquired throughout the diurnal cycle - typically this is done twice during a diurnal cycle, but we suggest multiple times. Comparison of images acquired over 24 hours requires that either the data be calibrated to surface temperature, or the response of the thermal camera is linear and stable over the image acquisition period. Depending on the type and age of the thermal instrument, imagery may be self-calibrated in radiance, corrected for atmospheric effects, and pixels converted to surface temperature. We used an experimental instrumentation where the calibration should be stable, but calibration coefficients are unknown. Cases may occur where one wishes to validate the camera's calibration. We present a method to validate and calibrate the instrument and characterize the thermal physical properties for areas of interest. Finally, in situ high-temporal-resolution oblique thermal imaging can be invaluable in preparation for conducting overflight missions. We present the following:•The use of oblique thermal high temporal resolution thermal imaging over diurnal or multiday periods for the characterization of landscapes has not been widespread but poses great potential.•A method of collecting and analyzing thermal data that can be used to either determine or validate thermal camera calibration coefficients.•An approach to characterize thermophysical properties of the landscape using oblique temporally high-resolution thermal imaging, combined with in situ ground measurements.

Oligotrophic glacial lakes in the Andes Mountains serve as models to study the effects of climate change on natural biological systems. The persistent high UV regime and evolution of the lake biota due to deglaciation make Andean lake ecosystems potential analogues in the search for life on other planetary bodies. Our objective was to identify microbial biomarkers and metabolic patterns that represent time points in the evolutionary history of Andean glacial lakes, as these may be used in long-term studies as microscale indicators of climate change processes. We investigated a variety of microbial markers in shallow sediments from Laguna Negra and Lo Encañado lakes (Región Metropolitana, Chile). An on-site immunoassay-based Life Detector Chip (LDChip) revealed the presence of sulfate-reducing bacteria, methanogenic archaea, and exopolymeric substances from Gammaproteobacteria. Bacterial and archaeal 16S rRNA gene sequences obtained from field samples confirmed the results from the immunoassays and also revealed the presence of Alpha-, Beta-, Gamma-, and Deltaproteobacteria, as well as cyanobacteria and methanogenic archaea. The complementary immunoassay and phylogenetic results indicate a rich microbial diversity with active sulfate reduction and methanogenic activities along the shoreline and in shallow sediments. Sulfate inputs from the surrounding volcanic terrains during deglaciation may explain the observed microbial biomarker and metabolic patterns, which differ with depth and between the two lakes. A switch from aerobic and heterotrophic metabolisms to anaerobic ones such as sulfate reduction and methanogenesis in the shallow shores likely reflects the natural evolution of the lake sediments due to deglaciation. Hydrodynamic deposition of sediments creates compartmentalization (e.g., sediments with different structure and composition surrounded by oligotrophic water) that favors metabolic transitions. Similar phenomena would be expected to occur on other planetary lakes, such as those of Titan, where watery niches fed by depositional events would be surrounded by a "sea" of hydrocarbons. Key Words: Glacier lakes-Sedimentation-Prokaryotic metabolisms and biomarkers-Deglaciation-Life detection-Planetary exploration. Astrobiology 18, 586-606.

On its way to Jupiter in 1990, the Galileo spacecraft searched for signs of life on Earth, providing a set of control experiments that continue to inform our quest to detect extraterrestrial life.

Earth's biological and environmental evolution are intertwined and inseparable. This coevolution has become a fundamental concept in astrobiology and is key to the search for life beyond our planet. In the case of Mars, whether a coevolution took place is unknown, but analyzing the factors at play shows the uniqueness of each planetary experiment regardless of similarities. Early Earth and early Mars shared traits. However, biological processes on Mars, if any, would have had to proceed within the distinctive context of an irreversible atmospheric collapse, greater climate variability, and specific planetary characteristics. In that, Mars is an important test bed for comparing the effects of a unique set of spatiotemporal changes on an Earth-like, yet different, planet. Many questions remain unanswered about Mars' early environment. Nevertheless, existing data sets provide a foundation for an intellectual framework where notional coevolution models can be explored. In this framework, the focus is shifted from planetary-scale habitability to the prospect of habitats, microbial ecotones, pathways to biological dispersal, biomass repositories, and their meaning for exploration. Critically, as we search for biosignatures, this focus demonstrates the importance of starting to think of early Mars as a biosphere and vigorously integrating an ecosystem approach to landing site selection and exploration. Key Words: Astrobiology—Biosignatures—Coevolution of Earth and life—Mars. Astrobiology 18, 1–27.

Since the initial experiments nearly 50 years ago, techniques for detecting caves using airborne and spacecraft acquired thermal imagery have improved markedly. These advances are largely due to a combination of higher instrument sensitivity, modern computing systems, and processor-intensive analytical techniques. Through applying these advancements, our goals were to: (1) Determine the efficacy of methods designed for terrain analysis and applied to thermal imagery, (2) evaluate the usefulness of predawn and midday imagery for detecting caves, and (3) ascertain which imagery type (predawn, midday, or the difference between those two times) was most informative. Using forward stepwise logistic (FSL) and Least Absolute Shrinkage and Selection Operator (LASSO) regression analyses for model selection, and a thermal imagery dataset acquired from the Mojave Desert, California, we examined the efficacy of three well-known terrain descriptors (i.e., slope, topographic position index (TPI), and curvature) on thermal imagery for cave detection. We also included the actual, untransformed thermal DN values (hereafter “unenhanced thermal”) as a fourth dataset. Thereafter, we compared the thermal signatures of known cave entrances to all non-cave surface locations. We determined these terrain-based analytical methods, which described the “shape” of the thermal landscape, hold significant promise for cave detection. All imagery types produced similar results. Down-selected covariates per imagery type, based upon the FSL models, were: Predawn— slope, TPI, curvature at 0 m from cave entrance, as well as slope at 1 m from cave entrance, midday— slope, TPI, and unenhanced thermal at 0 m from cave entrance, and difference— TPI and slope at 0 m from cave entrance, as well as unenhanced thermal and TPI at 3.5 m from cave entrance. We provide recommendations for future research directions in terrestrial and planetary cave detection using thermal imagery.

Summary: As part of the NASA Frontier Development Lab, we implemented a parallelized cloud-based exploration strategy to better understand the statistical distributions and properties of potential planetary atmospheres. Starting with a modern-day Earth atmosphere, we iteratively and incrementally simulated a range of atmospheres to infer the landscape of the multi-parameter space, such as the abundances of biological mediated gases that would yield stable (non-runaway) planetary atmospheres on Earth-like planets around solar-type stars. Our current dataset comprises of 124,314 simulated models of earth-like exoplanet atmospheres and is available publicly on the NASA Exoplanet Archive. Our scalable approach of analysing atmospheres could also help interpret future observations of planetary atmospheres by providing estimates of atmospheric gas fluxes and temperatures as a function of altitude, and thereby enable high-throughput first-order assessment of the potential habitability of exoplanetary surfaces. Introduction: The NASA Frontier Development Laboratory (FDL) is an annual science accelerator that focuses on applying machine learning and large-scale computing to challenges in space science and exploration (Cabrol et al. 2018). FDL engages interdisciplinary teams of computer scientists and space science domain experts and tasks them to solve problems that are valuable to NASA and humanity’s future. We implemented a cloud-based strategy to better understand the statistical distributions of habitable planets and life in the universe and layout an avenue to characterize the potential role of biological regulation of planetary atmospheres. We simulated a range of atmospheres to infer the landscape of the multi-parameter space, such as the abundances of biological mediated gases that would yield stable (non-runaway) planetary atmospheres on Earth-like planets around solar-type stars. Our scalable tool, once coupled to a generalized ecosystem model, could help derive estimates of the biological mediated atmospheric gas fluxes and help constrain the type and the extent of exobiology on exoplanets based on the remotely detected atmospheric compositions. Method: Our team generated data for a wide variety of hypothetical biospheres to scope out the plausible range of habitable atmospheres and metabolisms that could be present in the universe. We implemented a cloud-based massively parallelized procedural parameter search for a wide range of planetary atmospheres. Since existing tools were not capable of broad parameter scans, we streamlined the ATMOS 1-D atmospheric simulation code developed by the NASA Virtual Planetary Laboratory (Arney et al. 2016, Meadows et al. 2016). and produced a package for the community called PyAtmos (https://github.com/PyAtmos). This package dramatically increases the usability and accessibility of the ATMOS 1-D software across a range of platforms. We then used PyAtmos on the Google Cloud Platform in an automated and scalable procedure to search the parameter space of atmospheric compositions. Our search considered the relative concentrations of greenhouse gases such as methane, carbon dioxide and water. 124,314 different atmospheres were simulated and then analyzed to establish if the planetary surface temperatures and fluxes of gases were compatible with conditions that could maintain a liquid water inventory on the planetary surface. Results: The dataset of planetary atmospheres we have generated can be used for training machine learning models to bootstrap the ATMOS code. It is an open-source dataset (https://exoplanetarchive.ipac.caltech.edu/cgi-bin/FDL/nph-fdl?atmos) available for the community to understand distributions of habitability parameters such as surface temperatures and free energy available to life on different classes of atmosphere bearing planets. All of these are based around an Earth-like planet that orbits a star similar to the Sun, but with different gas mixtures in their atmospheres. A parameter space of possible atmospheres was scanned by varying the concentrations of six gases - Carbon dioxide, Oxygen, Water, Methane, Hydrogen and Nitrogen. In future work, we plan to include parameters such as star type, planet size and distance from the host star when evaluating the range of different atmospheres that may be habitable. The scalability of our framework provides a mechanism to incorporate complex biogeochemical and global climate models to better understand the co-evolution of the atmosphere and biosphere (e.g. Chopra et al. 2016, Gebauer et al. 2017, Nicholson et al. 2018, Lineweaver et al. 2018). Analyses of such multi-dimensional datasets will enable better interpretations of future observations of exo-atmospheres and biosignatures by upcoming telescopes (Fuji et al. 2018). References Arney, G. N. et al. (2016) The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth. Astrobiology, 16(11), 873–899. Cabrol, N. A., et al. (2018) Advancing Astrobiology Through Public/Private Partnership: The FDL Model. In: Lunar and Planetary Science Conference. Vol. 49. Lunar and Planetary Science Conference, 1275. Chopra, A. and Lineweaver, C. H. (2016) The Case for a Gaian Bottleneck: The Biology of Habitability. Astrobiology, 16(1), 7–22. Fujii, Y. et al. (2018) Exoplanet Biosignatures: Observational Prospects. Astrobiology, 18(6). Gebauer, S. et al. (2017) Evolution of Earth-like Extrasolar Planetary Atmospheres: Assessing the Atmospheres and Biospheres of Early Earth Analog Planets with a Coupled Atmosphere Biogeochemical Model. Astrobiology, 17(1), 27–54. Lineweaver, C. H. et al. (2018), The Evolution of Habitability: Characteristics of Habitable Planets, in Vera M. Kolb (Ed.) Handbook of Astrobiology, Taylor & Francis Meadows, V. S. et al. (2016) The Habitability of Proxima Centauri b: Environmental States and Observational Discriminants. Astrobiology, 18(2), 133– 189. Nicholson, A. E. et al. (2018). Gaian bottlenecks and planetary habitability maintained by evolving model biospheres: The ExoGaia model. Monthly Notices of the Royal Astronomical Society, 477(1), 727–740.

Solar radiation has been measured in the high Andes near Laguna Lejia (latitude 23° 26' 23.30" S, longitude 67° 38' 14.29" W) at an elevation of 4715 m between December 2016 and December 2017. Irradiances were monitored in four wavelength channels: PAR (400-700 nm), UV-A (315-400 nm), UV-B (295-315 nm) and short-wavelength UV-B (295-310 nm) with a new radiometer. In addition, ambient temperatures were recorded. Record values have been found for PAR (exceeding 600 W m-2 ), UV-A (close to 95 W m-2 ), UV-B (3.13 W m-2 ) and short-wavelength UV-B (0.144 W m-2 ) during Austral spring. The winter irradiance values slightly exceeded 50% of these values. Maximal cloud effects due to multiple reflections were 45, 38, 32 and 35% higher than values under cloudless skies for PAR, UV-A, UV-B and short-wavelength UV-B, respectively. Record irradiance for this site shows a UV index reaching and exceeding 20, which is due to low solar zenith angles, the altitude, low water vapor and aerosol concentrations in the atmosphere as well as low total column ozone concentrations.

The Atacama Desert, the oldest and driest desert on Earth, displays significant rains only once per decade. To investigate how microbial communities take advantage of these sporadic wet events, we carried out a geomicrobiological study a few days after a heavy rain event in 2015. Different physicochemical and microbial community analyses were conducted on samples collected from playas and an alluvial fan from surface, 10, 20, 50, and 80 cm depth. Gravimetric moisture content peaks were measured in 10 and 20 cm depth samples (from 1.65 to 4.1% w/w maximum values) while, in general, main anions such as chloride, nitrate, and sulfate concentrations increased with depth, with maximum values of 13-1,125; 168-10,109; and 9,904-30,952 ppm, respectively. Small organic anions such as formate and acetate had maximum concentrations from 2.61 to 3.44 ppm and 6.73 to 28.75 ppm, respectively. Microbial diversity inferred from DNA analysis showed Actinobacteria and Alphaproteobacteria as the most abundant and widespread bacterial taxa among the samples, followed by Chloroflexi and Firmicutes at specific sites. Archaea were mainly dominated by Nitrososphaerales, Methanobacteria, with the detection of other groups such as Halobacteria. Metaproteomics showed a high and even distribution of proteins involved in primary metabolic processes such as energy production and biosynthetic pathways, and a limited but remarkable presence of proteins related to resistance to environmental stressors such as radiation, oxidation, or desiccation. The results indicated that extra humidity in the system allows the microbial community to repair, and prepare for the upcoming hyperarid period. Additionally, it supplies biomarkers to the medium whose preservation potential could be high under strong desiccation conditions and relevant for planetary exploration.

Sediments in the hyper-arid core of the Atacama Desert are a terrestrial analogue to Mars regolith. Understanding the distribution and drivers of microbial life in the sediment may give critical clues on how to search for biosignatures on Mars. Here, we identify the spatial distribution of highly specialised bacterial communities in previously unexplored depth horizons of subsurface sediments. We deployed an autonomous rover in a mission-relevant Martian drilling scenario with manual sample validation. Subsurface communities were delineated by depth related to sediment moisture. Geochemical analysis indicated soluble salts and minerology that influenced water bio-availability, particularly in deeper sediments. Colonization was also patchy and uncolonized sediment was associated with indicators of extreme osmotic challenge. The study identifies linkage between biocomplexity, moisture and geochemistry in Mars-like sediments at the limit of habitability and demonstrates feasibility of the rover-mounted drill for future Mars sample recovery.

Binary choice experiments under natural solar radiation were used to test short-term behavioral responses of freshwater calanoid copepods to ultraviolet radiation (UV). Responses of the nine species from 15 populations spanning North and South America included both UV attraction and UV avoidance, and varied among habitats, species and populations. Copepods from more transparent lakes were more attracted to UV than those from less transparent lakes. When individuals were pre-exposed in the laboratory to photosynthetically active radiation (PAR) in the presence and absence of UV, those pre-exposed to UV spent more time in the high UV environment than those exposed to PAR alone. However, these differences disappeared after 150 min, suggesting that the responses were short term and mediated in part by ambient UV conditions. Copepods represent a large proportion of the biomass of zooplankton in many aquatic ecosystems, and their ability to detect and respond behaviorally to UV may enable them to use this ubiquitous environmental cue to regulate their water column position. The use of UV as a habitat selection cue may permit copepods to exploit optimal food environments or limit overlap with less UV-tolerant competitors, predators or parasites, while minimizing damage resulting from longer term UV exposure.

Scattering of solar radiation by clouds can reduce or enhance solar global irradiance compared to cloudless-sky irradiance at the Earth’s surface. Cloud effects to global irradiance can be described by Cloud Modification Factors (CMF). Depending on strength and duration, irradiance enhancements affect the energy balance of the surface and gain of solar power for electric energy generation. In the ultraviolet region, they increase the risk for damage to living organisms. Wavelength-dependent CMFs have been shown to reach 1.5 even in the UV-B region at low altitudes. Ground-based solar radiation measurements in the high Andes region at altitudes up to 5917 m a.s.l showed cloud-induced irradiance enhancements. While UV-A enhancements were explained by cloud scattering, both radiation scattering from clouds and Negative Ozone Anomalies (NOA) have been discussed to have caused short-time enhancement of UV-B irradiance. Based on scenarios using published CMF and additional spectroradiometric measurements at a low-altitude site, the contribution of cloud scattering to the UV-B irradiance enhancement in the Andes region has been estimated. The range of UV index estimates converted from measured UV-B and UV-A irradiance and modeled cloudless-sky ratios UV-B/erythemal UV is compatible with an earlier estimate of an extreme UV index value of 43 derived for the high Andes.

Laser Raman spectroscopy (LRS) has been proposed for in situ characterization of molecular species in planetary surface exploration, and three laser Raman spectrometers are included in the science payloads of two under-development missions to Mars (ESA-ExoMars2018 and NASA-Mars2020). We report the first rover test of a laser Raman spectrometer developed for flight, the Mars Micro-beam Raman Spectrometer (MMRS) in the Atacama Desert (Chile). The MMRS was integrated on the Zoe rover and analyzed subsurface samples brought up by a 1 m drill and delivered by a carousel. The MMRS demonstrated robust performance over 50-km traverse on rugged terrains. From MMRS data, igneous minerals, carbonates, sulfates and carbonaceous materials were unambiguously identified. Quantified distributions of major minerals and carbonaceous materials are extracted from MMRS results, which can be used to imply the regional geological evolution, and potential bioactivities. MMRS in the field performed as well as an LRS laboratory instrument when MMRS was focused satisfactorily. The discovery of stable γ-anhydrite, in large quantity (20% in a sample), in the Atacama soils raises an important question of its stability in the field in a natural environment that is worth further laboratory experimental investigation. Copyright © 2015 John Wiley & Sons, Ltd.

The MAVEN mission has provided evidence that most of the early Martian atmosphere was stripped away early by solar wind. For the major part of the planet’s history, low gravity and weak magnetic field have hardly shielded the surface from the high energetic particles. Yet, thermal differences between day and night and large storms regularly inject substantial amount of dust in the atmosphere, which can preclude solar radiation from significantly penetrating to the surface. The radiation environment of Mars is thus complex, and characterizing its evolution through time is essential to understand (a) the impact of UV radiation on soil geochemistry and its role in the preservation of biosignatures in the geologic record, and (b) the UV environment and adaptation potential of early subaerial microbial habitats, which are examined here.

Searching for biosignatures on Mars is changing the focus of exploration from the characterization of habitability to the investigation of a potential coevolution, that is, the spatiotemporal interactions of life with its environment. Yet, the intellectual framework underpinning the preparation of Mars 2020 and ExoMars along with future life-seeking missions is essentially the same as the one that has guided the exploration of Mars for the past 15 years (e.g., Mustard et al., 2013 , Hays et al., 2017 , Cabrol, 2018 ); see also Chapters 11 and 12 . This framework is articulated around the terrestrial analogy principle of habitability. While this principle is helpful in characterizing Mars habitability potential over time, it is limiting and potentially misleading for the exploration of biosignatures as its focus is primarily on the spatiotemporal dynamics of environmental factors.

A next challenge in planetary exploration involves probing the subsurface to understand composition, to search for volatiles like water ice, or to seek evidence of life. The Mars rover missions have scraped the surface of Mars and cored rocks to make ground breaking discoveries. Many believe that the chance of finding evidence of life is expected to increase by going deeper. Deploying a system that probes the subsurface brings its own challenges and to that end, we designed, built and field tested an autonomous robot that can collect subsurface samples using a 1 m drill. The drill operation, sample transfer, and sample analysis are all automated. The robot also navigates kilometers autonomously while making decisions about scientific measurements. The system is designed to execute multi-day science plans, stopping and resuming operation as necessary. This paper describes the robot and science instruments and lessons from designing and operating such a system.

This field report describes the design and operations of the Planetary LakeLander PLL probe and its ground data systems. LakeLander's primary mission is to characterize the physical, chemical, and biological processes occurring in a high-altitude lake, and how they are being impacted by rapid deglaciation. LakeLander's secondary purpose is to test operation concepts for future exploration of Titan's lakes. The LakeLander probe is a permanently anchored buoy that measures both surface meteorology and water quality parameters in the top 40i¾?m of the water column. The concept of operations calls for the probe to continue collecting and downlinking data through the Andean winter, when the lake is inaccessible; this drives the power system design and forces a strong focus on system reliability, analogous to a space mission. The PLL ground data system provides the central archive of downlinked data. They are structured around a unified data-sharing web site that includes tools for mapping, data visualization, documentation, and numerical analysis. The web site provides a hub for engaging the science team and enables interdisciplinary collaboration. This report concludes with lessons learned during field deployment and several months of remote operations on the lake. Among the conclusions: 1 the choice to use an off-the-shelf profiling system has proven wise; 2 effective maintenance of a long-lived remote system requires extensive measurement, logging, and display of as many system variables as possible; and 3 the visualization sandbox component of the data-sharing web site has made numerical analysis of probe data much easier and more accessible to the entire interdisciplinary science team.

Transparency is a fundamental characteristic of aquatic ecosystems and is highly responsive to changes in climate and land use. The transparency of glacially-fed lakes may be a particularly sensitive sentinel characteristic of these changes. However, little is known about the relative contributions of glacial flour versus other factors affecting light attenuation in these lakes. We sampled 18 glacially-fed lakes in Chile, New Zealand, and the U.S. and Canadian Rocky Mountains to characterize how dissolved absorption, algal biomass (approximated by chlorophyll a), water, and glacial flour contributed to attenuation of ultraviolet radiation (UVR) and photosynthetically active radiation (PAR, 400–700 nm). Variation in attenuation across lakes was related to turbidity, which we used as a proxy for the concentration of glacial flour. Turbidity-specific diffuse attenuation coefficients increased with decreasing wavelength and distance from glaciers. Regional differences in turbidity-specific diffuse attenuation coefficients were observed in short UVR wavelengths (305 and 320 nm) but not at longer UVR wavelengths (380 nm) or PAR. Dissolved absorption coefficients, which are closely correlated with diffuse attenuation coefficients in most non-glacially-fed lakes, represented only about one quarter of diffuse attenuation coefficients in study lakes here, whereas glacial flour contributed about two thirds across UVR and PAR. Understanding the optical characteristics of substances that regulate light attenuation in glacially-fed lakes will help elucidate the signals that these systems provide of broader environmental changes and forecast the effects of climate change on these aquatic ecosystems.

Processes, environments, and the energy associated with the transport and deposition of sand at Gusev Crater are characterized at the microscopic scale through the comparison of statistical moments for particle size and shape distributions. Bivariate and factor analyses define distinct textural groups at 51 sites along the traverse completed by the Spirit rover as it crossed the plains and went into the Columbia Hills. Fine-to-medium sand is ubiquitous in ripples and wind drifts. Most distributions show excess fine material, consistent with a predominance of wind erosion over the last 3.8 billion years. Negative skewness at West Valley is explained by the removal of fine sand during active erosion, or alternatively, by excess accumulation of coarse sand from a local source. The coarse to very coarse sand particles of ripple armors in the basaltic plains have a unique combination of size and shape. Their distribution display significant changes in their statistical moments within the ~400 m that separate the Columbia Memorial Station from Bonneville Crater. Results are consistent with aeolian and/or impact deposition, while the elongated and rounded shape of the grains forming the ripples, as well as their direction of origin, could point to Ma'adim Vallis as a possible source. For smaller particles on the traverse, our findings confirm that aeolian processes have dominated over impact and other processes to produce sands with the observed size and shape patterns across a spectrum of geologic (e.g., ripples and plains soils) and aerographic settings (e.g., wind shadows).

The future exploration of Mars will require access to the subsurface, along with acquisition of samples for scientific analysis and ground-truthing of water ice and mineral reserves for in situ resource utilization. The Icebreaker drill is an integral part of the Icebreaker mission concept to search for life in ice-rich regions on Mars. Since the mission targets Mars Special Regions as defined by the Committee on Space Research (COSPAR), the drill has to meet the appropriate cleanliness standards as requested by NASA's Planetary Protection Office. In addition, the Icebreaker mission carries life-detection instruments; and in turn, the drill and sample delivery system have to meet stringent contamination requirements to prevent false positives. This paper reports on the development and testing of the Icebreaker drill, a 1 m class rotary-percussive drill and triple redundant sample delivery system. The drill acquires subsurface samples in short, approximately 10 cm bites, which makes the sampling system robust and prevents thawing and phase changes in the target materials. Autonomous drilling, sample acquisition, and sample transfer have been successfully demonstrated in Mars analog environments in the Arctic and the Antarctic Dry Valleys, as well as in a Mars environmental chamber. In all environments, the drill has been shown to perform at the "1-1-100-100" level; that is, it drilled to 1 m depth in approximately 1 hour with less than 100 N weight on bit and approximately 100 W of power. The drilled substrate varied and included pure ice, ice-rich regolith with and without rocks and with and without 2% perchlorate, and whole rocks. The drill is currently at a Technology Readiness Level (TRL) of 5. The next-generation Icebreaker drill weighs 10 kg, which is representative of the flightlike model at TRL 5/6.

[1] Science missions have limited lifetimes, necessitating an efficient investigation of the field site. The efficiency of onboard cameras, critical for planning, is limited by the need to downlink images to Earth for every decision. Recent advances have enabled rovers to take follow-up actions without waiting hours or days for new instructions. We propose using built-in processing by the instrument itself for adaptive data collection, faster reconnaissance, and increased mission science yield. We have developed a machine learning pixel classifier that is sensitive to texture differences in surface materials, enabling more sophisticated onboard classification than was previously possible. This classifier can be implemented in a Field Programmable Gate Array (FPGA) for maximal efficiency and minimal impact on the rest of the system's functions. In this paper, we report on initial results from applying the texture-sensitive classifier to three example analysis tasks using data from the Mars Exploration Rovers.

[1] We performed laboratory laser-induced breakdown spectroscopy (LIBS) and laser Raman spectroscopy measurements on samples from a layered outcrop from the Atacama Desert, Chile. This outcrop is a terrestrial morphological and possibly mineralogical analogue for similar formations that will likely be investigated by the Curiosity rover at Gale Crater. Our results demonstrate that fast LIBS analysis can generate semiquantitative chemical profiles in subminute times using automated data processing tools. Therefore, the LIBS instrument can be an invaluable tactical tool on the Curiosity rover for remote, rapid geochemical survey of layered outcrops, thus serving daily operational needs. The derived chemical profiles, supported by the range of minerals identified by Raman spectroscopy, is consistent with the products of a continental evaporitic lake. In the framework of future surface exploration on Mars, a combined Raman/LIBS investigation may provide a rapid mineralogical/chemical evaluation of targets that can be useful for selecting samples to be eventually collected for sample return purposes or for selecting sample sites to be drilled in the search for astrobiology-relevant species.

A scale model of the proposed Titan Mare Explorer capsule was deployed at the Planetary Lake Lander field site at Laguna Negra, Chile. The tests served to calibrate models of wind-driven drift of the capsule and to understand its attitude motion in the wave field, as well as to identify dynamic and acoustic signatures of shoreline approach. This information enables formulation of onboard trigger criteria for near-shore science data acquisition. Key Words: Titan—Vehicle dynamics—Science autonomy—Lake. Astrobiology 17, xxx–xxx.