Putative indigenous carbon-bearing alteration features in martian meteorite Yamato 000593

A predictive model for the ichnological suitability of the Jezero crater, Mars: searching for fossilized traces of life-substrate interactions in the 2020 Rover Mission Landing Site

Ichnofossils, the fossilized products of life-substrate interactions, are among the most abundant biosignatures on Earth and therefore they may provide scientific evidence of potential life that may have existed on Mars. Ichnofossils offer unique advantages in the search for extraterrestrial life, including the fact that they are resilient to processes that obliterate other evidence for past life, such as body fossils, as well as chemical and isotopic biosignatures. The goal of this paper is evaluating the suitability of the Mars 2020 Landing Site for ichnofossils. To this goal, we apply palaeontological predictive modelling, a technique used to forecast the location of fossil sites in uninvestigated areas on Earth. Accordingly, a geographic information system (GIS) of the landing site is developed. Each layer of the GIS maps the suitability for one or more ichnofossil types (bioturbation, bioerosion, biostratification structures) based on an assessment of a single attribute (suitability factor) of the Martian environment. Suitability criteria have been selected among the environmental attributes that control ichnofossil abundance and preservation in 18 reference sites on Earth. The goal of this research is delivered through three predictive maps showing which areas of the Mars 2020 Landing Site are more likely to preserve potential ichnofossils. On the basis of these maps, an ichnological strategy for the Perseverance rover is identified, indicating (1) 10 sites on Mars with high suitability for bioturbation, bioerosion and biostratification ichnofossils, (2) the ichnofossil types, if any, that are more likely to be present at each site, (3) the most efficient observation strategy for detecting eventual ichnofossils. The predictive maps and the ichnological strategy can be easily integrated in the existing plans for the exploration of the Jezero crater, realizing benefits in life-search efficiency and cost-reduction.

A New Constraint on the Physicochemical Condition of Mars Surface during the Amazonian Epoch Based on Chemical Speciation for Secondary Minerals in Martian Nakhlites

Iddingsite in Martian nakhlites contains various secondary minerals that reflect water–rock interaction on Mars. However, the formation processes of secondary Fe minerals in iddingsite are unclear because they include carbonates precipitated under reductive and alkaline conditions and sulfates that are generally precipitated under oxidative and acidic conditions. Mineral types cannot coexist under equilibrium. Herein, we characterize the carbonate phase of meteorite Yamato 000593 as siderite and Mn-bearing siderite via field-emission electron probe microanalyzer (FE-EPMA). Then, we examined the distribution and speciation of trace Cr and S within the carbonates through synchrotron micro-focused X-ray fluorescence-X-ray absorption fine structure and scanning transmission X-ray microscopy (μ-XRF-XAFS/STXM) analysis to estimate the transition history of Eh-pH conditions during siderite formation to explain the coexistence of carbonate and sulfate phases in the nakhlite vein. Specifically, the distribution and speciation of S in the mesostasis and carbonate phases and the heterogeneous distribution of Mn-FeCO3 incorporating Cr(III) in the carbonate constrain the Eh-pH condition. The conditions and transition of the fluid chemistry determined herein based on speciation of various elements provide a new constraint on the physicochemical condition of the water that altered the nakhlite body during the Amazonian epoch.

Critically testing olivine-hosted putative martian biosignatures in the Yamato 000593 meteorite-Geobiological implications

On rocky planets such as Earth and Mars the serpentinization of olivine in ultramafic crust produces hydrogen that can act as a potential energy source for life. Direct evidence of fluid-rock interaction on Mars comes from iddingsite alteration veins found in martian meteorites. In the Yamato 000593 meteorite, putative biosignatures have been reported from altered olivines in the form of microtextures and associated organic material that have been compared to tubular bioalteration textures found in terrestrial sub-seafloor volcanic rocks. Here, we use a suite of correlative, high-sensitivity, in situ chemical, and morphological analyses to characterize and re-evaluate these microalteration textures in Yamato 000593, a clinopyroxenite from the shallow subsurface of Mars. We show that the altered olivine crystals have angular and micro-brecciated margins and are also highly strained due to impact-induced fracturing. The shape of the olivine microalteration textures is in no way comparable to microtunnels of inferred biological origin found in terrestrial volcanic glasses and dunites, and rather we argue that the Yamato 000593 microtextures are abiotic in origin. Vein filling iddingsite extends into the olivine microalteration textures and contains amorphous organic carbon occurring as bands and sub-spherical concentrations <300 nm across. We propose that a martian impact event produced the micro-brecciated olivine crystal margins that reacted with subsurface hydrothermal fluids to form iddingsite containing organic carbon derived from abiotic sources. These new data have implications for how we might seek potential biosignatures in ultramafic rocks and impact craters on both Mars and Earth.

Tunnel Formation in Basalt Glass

We propose a model whereby microscopic tunnels form in basalt glass in response to a natural proton flux from seawater into the glass. This flux is generated by the alteration of the glass as protons from water replace cations in the glass. In our proton gradient model, cells are gateways through which protons enter and alter the glass and through which cations leave the glass. In the process, tunnels are formed, and cells derive energy from the proton and ion fluxes. Proton flux from seawater into basalt glass would have occurred on Earth as soon as water accumulated on the surface and would have preceded biological redox catalysis. Tunnels in modern basalts are similar to tunnels in Archean basalts, which may be our earliest physical evidence of life. Proton gradients like those described in this paper certainly exist on other planetary bodies where silicate rocks are exposed to acidic to slightly alkaline water.

Lunar and Martian Silica

Silica polymorphs, such as quartz, tridymite, cristobalite, coesite, stishovite, seifertite, baddeleyite-type SiO2, high-pressure silica glass, moganite, and opal, have been found in lunar and/or martian rocks by macro-microanalyses of the samples and remote-sensing observations on the celestial bodies. Because each silica polymorph is stable or metastable at different pressure and temperature conditions, its appearance is variable depending on the occurrence of the lunar and martian rocks. In other words, types of silica polymorphs provide valuable information on the igneous process (e.g., crystallization temperature and cooling rate), shock metamorphism (e.g., shock pressure and temperature), and hydrothermal fluid activity (e.g., pH and water content), implying their importance in planetary science. Therefore, this article focused on reviewing and summarizing the representative and important investigations of lunar and martian silica from the viewpoints of its discovery from lunar and martian materials, the formation processes, the implications for planetary science, and the future prospects in the field of “micro-mineralogy”.

The Characterization of Biosignatures in Caves Using an Instrument Suite

The search for life and habitable environments on other Solar System bodies is a major motivator for planetary exploration. Due to the difficulty and significance of detecting extant or extinct extraterrestrial life in situ, several independent measurements from multiple instrument techniques will bolster the community's confidence in making any such claim. We demonstrate the detection of subsurface biosignatures using a suite of instrument techniques including IR reflectance spectroscopy, laser-induced breakdown spectroscopy, and scanning electron microscopy/energy dispersive X-ray spectroscopy. We focus our measurements on subterranean calcium carbonate field samples, whose biosignatures are analogous to those that might be expected on some high-interest astrobiology targets. In this work, we discuss the feasibility and advantages of using each of the aforementioned instrument techniques for the in situ search for biosignatures and present results on the autonomous characterization of biosignatures using multivariate statistical analysis techniques. Key Words: Biosignature suites-Caves-Mars-Life detection. Astrobiology 17, 1203-1218.

A Hierarchical System for Evaluating the Biogenicity of Metavolcanic- and Ultramafic-Hosted Microalteration Textures in the Search for Extraterrestrial Life

The low-temperature alteration of submarine volcanic glasses has been argued to involve the activity of microorganisms, and analogous fluid-rock-microbial-mediated alteration has also been postulated on Mars. However, establishing the extent to which microbes are involved in volcanic glass alteration has proven to be difficult, and the reliability of resulting textural biosignatures is debated, particularly in the early rock record. We therefore propose a hierarchical scheme to evaluate the biogenicity of candidate textural biosignatures found in altered terrestrial and extraterrestrial basaltic glasses and serpentinized ultramafic rocks. The hierarchical scheme is formulated to give increasing confidence of a biogenic origin and involves (i) investigation of the textural context and syngenicity of the candidate biosignature; (ii) characterization of the morphology and size range of the microtextures; (iii) mapping of the geological and physicochemical variables controlling the occurrence and preservation of the microtextures; (iv) in situ investigation of chemical signatures that are syngenetic to the microtexture; and (v) identification of growth patterns suggestive of biological behavior and redox variations in the host minerals. The scheme results in five categories of candidate biosignature as follows: Category 1 indicates preservation of very weak evidence for biogenicity, Categories 2 through 4 indicate evidence for increasing confidence of a biogenic origin, and Category 5 indicates that biogenic origin is most likely. We apply this hierarchical approach to examine the evidence for a biogenic origin of several examples, including candidate bacterial encrustations in altered pillow lavas, granular and tubular microtextures in volcanic glass from the subseafloor and a Phanerozoic ophiolite, mineralized microtextures in Archean metavolcanic glass, and alteration textures in olivines of the martian meteorite Yamato 000593. The aim of this hierarchical approach is to provide a framework for identifying robust biosignatures of microbial life in the altered oceanic crust on Earth, and in extraterrestrial altered mafic-ultramafic rocks, particularly on Mars.