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Northwest Africa 6963 (NWA 6963) is a coarse-grained, gabbroic Martian meteorite that further extends our Martian sample collection, both compositionally and texturally. Gabbroic shergottite NWA 6963 provides direct petrologic evidence of intrusive igneous conditions within the Martian crust. Here, we analyzed geochemical zoning profiles and microstructural-crystallographic information from electron backscattered diffraction of augite and pigeonite to constrain the crystallization history of NWA 6963. Compositional zoning profiles reveal pyroxenes with augite or pigeonite cores mantled by Fe-rich pigeonite rims. Our results suggest complex pyroxene textures and zoning profiles observed in pyroxenes in NWA 6963 are due to pyroxene accumulation from a crystallizing magma in a large intrusive environment (sill or magma chamber); however, without geologic context or companion samples, it is currently impossible to rule out accumulation at the base of a very large (>>100 m) differentiated flow.

As the exploration of Mars and other worlds for signs of life has increased, the need for a common nomenclature and consensus has become significantly important for proper identification of nonterr...

A number of new Venus mission concepts are being currently evaluated for final approval, such as the NASA VERITAS and DAVINCI+, the Roscosmos-NASA Venera-D and the ESA EnVision proposals. These missions would analyze different aspects of the Earth’s twin planet: the chemistry and structure of its atmosphere, the spectral characteristics and composition of its surface, and its gravity anomalies. The wealth of high-resolution data to be produced by these future missions would likely shed new light on the major science questions. In this regard, one of the major debates concerns whether Venus underwent (and it is currently undergoing) through several episodes of abrupt and catastrophic resurfacing which rejuvenated its entire surface in a short amount of time, or its volcanism has been more steady and constant in time. Recent studies of Imdr Regio, one of the young volcanic rises, have provided hints indicating that volcanic as well as tectonic activity may be still ongoing in that area. The young volcanic rises are generated and supported by underlying active mantle plumes and can be considered as the some of the youngest geologic terrains of Venus. Studying how the rate and styles of volcanic and tectonic activities are evolving through time will tell us more about the interior structure of Venus, shedding some light on the major debate between catastrophic and equilibrium resurfacings. For this reason, we propose here the young volcanic rises, and in particular Idunn Mons of Imdr Regio, as potential target sites for future orbital and in-situ investigations.

Here, we calculate the mineralogy of the Martian lower crust and upper mantle as a function of pressure and temperature with depth using four bulk compositions (average crust, Gusev basalt, olivine‐phyric shergottite, and primitive average mantle). We then use this mineralogy to extract rock properties such as density and seismic velocities, describe their changes with varying conditions and geotherms, and make predictions for the crust–mantle boundary. Mineralogically, all compositions produce garnet, orthopyroxene, clinopyroxene in varying proportions at high pressures, with differences in minor minerals (spinel, ilmenite, rutile, and/or K‐feldspar). According to our calculations, the average crust and Gusev basalt compositions have the potential to yield higher densities than the average mantle composition, particularly for thicker crusts and/or colder geotherms. Therefore, recycling of the Martian crust into the mantle could occur through the process of crustal delamination, if not kinetically inhibited. However, our results show that, depending on crustal thickness, the crust may not be easily distinguishable from the mantle in seismic properties.

Long-wavelength magnetic anomalies (LWMA) are broad scale variations of the magnetic field that are usually observed at high altitudes with amplitudes ranging up to about 20 nT. The source of these anomalies has typically been assumed to reside within the crust with negligible contributions from the lithospheric mantle. Recent work on the magnetization of mantle xenoliths suggests a possible lithospheric mantle contribution to LWMA, depending on tectonic setting and local geotherm. Here, we investigate the potential contribution of the lithospheric mantle to LWMA across two contrasting lithospheric geotherms: cratons and hotspots. To constrain the range of possible mantle contributions to satellite-observable LWMA in these settings, we develop a Monte Carlo suite of forward models of magnetic anomalies patterned after the mantle portions of the Siberian craton, the Hawai'i hotspot, and the French Massif Central plume. The models incorporate the current geotherms, the pressure dependence of the Curie temperature of magnetite, and the statistical distributions of rock magnetic data from mantle xenoliths in the specific regions. The Siberian craton shows the highest potential contribution of the mantle to LWMA with amplitudes of a few nT over wavelengths scaling to the long-axis of the craton. The Hawai'i hotspot region displays a potential contribution from the lithospheric mantle to satellite-measured magnetic anomalies on the order of 1 nT, while the Massif Central plume regions shows an insignificant contribution to satellite magnetic anomalies from lithospheric mantle. When compared with observed lithospheric total field anomalies derived from Swarm satellite data, the results show that the lithospheric mantle may contribute a few tens of percent to LWMA observed at satellite altitudes in specific regions depending on the average remanent magnetization in mantle minerals, the thickness of magnetized mantle (which depends on the geotherm), and the spatial extent of the region under consideration.

We report an infrared (IR) spectroscopic technique to detect quartz grains with large isotope anomalies. We synthesized isotopically doped quartz and used Fourier transform infrared spectroscopy (FT-IR) in two different instruments: a traditional far-field instrument and a neaSpec nanoFT-IR, to quantify the shift in the peak of the Si–O stretch near 780 cm−1 as a function of isotope composition, and the uncertainty in this shift. From these measurements, we estimated the minimum detectable isotope anomaly using FT-IR. The described technique can be used to nondestructively detect very small (30 nm) presolar grains. In particular, supernova grains, which can have very large isotope anomalies, are detectable by this method.

The physical processes active during the first billion years (FBY) of Earth's history, such as accretion, differentiation, and impact cratering, provide constraints on the initial conditions that were conducive to the formation and establishment of life on Earth. This motivated the Lunar and Planetary Institute's FBY topical initiative, which was a four-part conference series intended to look at each of these physical processes to study the basic structure and composition of our Solar System that was set during the FBY. The FBY Habitability conference, held in September 2019, was the last in this series and was intended to synthesize the initiative; specifically, to further our understanding of the origins of life, planetary and environmental habitability, and the search for life beyond Earth. The conference included discussions of planetary habitability and the potential emergence of life on bodies within our Solar System, as well as extrasolar systems by applying our knowledge of the Solar System's FBY, and in particular Earth's early history. To introduce this Special Collection, which resulted from work discussed at the conference, we provide a review of the main themes and a synopsis of the FBY Habitability conference.

Habitability has been generally defined as the capability of an environment to support life. Ecologists have been using Habitat Suitability Models (HSMs) for more than four decades to study the habitability of Earth from local to global scales. Astrobiologists have been proposing different habitability models for some time, with little integration and consistency among them, being different in function to those used by ecologists. Habitability models are not only used to determine if environments are habitable or not, but they also are used to characterize what key factors are responsible for the gradual transition from low to high habitability states. Here we review and compare some of the different models used by ecologists and astrobiologists and suggest how they could be integrated into new habitability standards. Such standards will help to improve the comparison and characterization of potentially habitable environments, prioritize target selections, and study correlations between habitability and biosignatures. Habitability models are the foundation of planetary habitability science and the synergy between ecologists and astrobiologists is necessary to expand our understanding of the habitability of Earth, the Solar System, and extrasolar planets., Published in Astrobiology, 21(8). arXiv admin note: substantial text overlap with arXiv:2007.05491

As the exploration of Mars and other worlds for signs of life has increased, the need for a common nomenclature and consensus has become significantly important for proper identification of nonterrestrial/non-Earth biology, biogenic structures, and chemical processes generated from biological processes. The fact that Earth is our single data point for all life, diversity, and evolution means that there is an inherent bias toward life as we know it through our own planet's history. The search for life “as we don't know it” then brings this bias forward to decision-making regarding mission instruments and payloads. Understandably, this leads to several top-level scientific, theoretical, and philosophical questions regarding the definition of life and what it means for future life detection missions. How can we decide on how and where to detect known and unknown signs of life with a single biased data point? What features could act as universal biosignatures that support Darwinian evolution in the geological context of nonterrestrial time lines? The purpose of this article is to generate an improved nomenclature for terrestrial features that have mineral/microbial interactions within structures and to confirm which features can only exist from life (biotic), features that are modified by biological processes (biogenic), features that life does not affect (abiotic), and properties that can exist or not regardless of the presence of biology (abiogenic). These four categories are critical in understanding and deciphering future returned samples from Mars, signs of potential extinct/ancient and extant life on Mars, and in situ analyses from ocean worlds to distinguish and separate what physical structures and chemical patterns are due to life and which are not. Moreover, we discuss hypothetical detection and preservation environments for extant and extinct life, respectively. These proposed environments will take into account independent active and ancient in situ detection prospects by using previous planetary exploration studies and discuss the geobiological implications within an astrobiological context.

Volcanic features and impact craters are ubiquitous features on Mars, and hydrothermal systems associated with the production of these features should have been abundant in Mars’s early history. These hydrothermal systems represent potentially habitable environments and are therefore a high priority for continued investigations of the Martian crust. Here we present a Mars analog study where basaltic magma intruded water-bearing sediments to produce a high-temperature (as high as ∼700°C) hydrothermal system, which we use to constrain the potential habitability of similar systems on Mars via mineralogy and geochemistry including S, C, and O isotopic systematics. Our analog site suggests evidence for a habitable environment once the system cooled below 120°C and the potential presence of microbial activity based on the combination of dolomite and C-isotopic systems in the same sample. These findings highlight the importance of future missions to investigate the interface of sediments with magmas and/or late-stage impact melts where microbial life may have taken hold when temperature conditions allowed.

This white paper summarizes the scientific importance of studying igneous compositions in meteorites, surface samples, and through orbital analyses to better constrain the geology of Mars as a whole and better understand the geological processes that have shaped Mars in the past and present. In support of martian igneous studies, we strongly advocate for the following in the upcoming decade: 1. To sustain funding for meteorite recovery in order to have continued access to martian samples; 2. To support the return of igneous samples from Jezero crater; 3. To support funding for detailed analyses of igneous rocks at the martian surface; 4. To support laboratories and collaborations between sample, remote-sensing, and mission scientists; 5. To support curation facilities needed for not only meteorite samples, but also Mars sample return. The study of martian igneous compositions is crucial to the entire planetary community as it will help us to resolve questions about the formation and evolution of planetary interiors, climate and atmospheres, as well as habitability throughout the entire solar system.

A White Paper in support of the 2023–2032 Planetary Science and Astrobiology Decadal Survey

Indicator minerals have special physical and chemical properties that can be analyzed to glean information concerning the composition of host rocks and formational (or altering) fluids. Clay, zeolite, and tourmaline mineral groups are all ubiquitous at the Earth’s surface and shallow crust and distributed through a wide variety of sedimentary, igneous, metamorphic, and hydrothermal systems. Traditional studies of indicator mineral-bearing deposits have provided a wealth of data that could be integral to discovering new insights into the formation and evolution of naturally occurring systems. This study evaluates the relationships that exist between different environmental indicator mineral groups through the implementation of machine learning algorithms and network diagrams. Mineral occurrence data for thousands of localities hosting clay, zeolite, and tourmaline minerals were retrieved from mineral databases. Clustering techniques (e.g., agglomerative hierarchical clustering and density based spatial clustering of applications with noise) combined with network analyses were used to analyze the compiled dataset in an effort to characterize and identify geological processes operating at different localities across the United States. Ultimately, this study evaluates the ability of machine learning algorithms to act as supplementary diagnostic and interpretive tools in geoscientific studies.

Low‐grade metamorphic hydrous minerals and carbonates occur in various settings on Mars and in Martian meteorites. We present constraints on the stability of prehnite, zeolites, serpentine, and carbonates by modeling the influence of H2O‐CO2 fluids during low‐grade metamorphism in the Martian crust using compositions of a Martian basalt and an ultramafic cumulate. In basaltic compositions with 5 wt% fluid, our models predict prehnite in less oxidized, CO2‐poor conditions (≤0.44 mol kg−1 CO2) on warmer geotherms of 20 °C km−1. At fluid‐saturated conditions, epidote and laumontite are replaced by quartz, calcite, chlorite, and muscovite. In ultramafic compositions with 5 wt% fluid, antigorite (serpentine) is stable at CO2‐poor conditions of ≤0.33 mol kg−1, while talc forms at 0.05–0.56 mol kg−1 CO2. At fluid‐saturated conditions, antigorite is replaced by talc and chlorite, and at higher X(CO2) by magnesite and quartz. Our models therefore suggest that prehnite, zeolites, and serpentine have formed in a CO2‐poor environment on Mars implying that fluids during their formation either did not contain high amounts of CO2 or had degassed CO2. Carbonates and potentially talc would have formed in the presence of a CO2‐bearing fluid and therefore at different alteration stages than for prehnite, zeolites, and serpentine either in the same hydrothermal event during which the fluid composition changed gradually due to cooling and precipitation or by separate and successive alteration events with fluids of different compositions.

NASA’s search for habitable environments has focused on alteration mineralogy of the Martian crust and the formation of hydrous minerals, because they reveal information about the fluid and environmental conditions from which they precipitated. Extensive work has focused on the formation of alteration minerals at low temperatures, with limited work investigating metamorphic or high-temperature alteration. We have investigated such a site as an analog for Mars: a mafic dike on the Colorado Plateau that was hydrothermally altered from contact with groundwater as it was emplaced in the porous and permeable Jurassic Entrada sandstone. Our results show evidence for fluid mobility removing Si and K but adding S, Fe, Ca, and possibly Mg to the system as alteration progresses. Mineralogically, all samples contain calcite, hematite, and kaolinite; with most samples containing minor anatase, barite, halite, and dolomite. The number of alteration minerals increase with alteration. The hydrothermal system that formed during interaction of the magma (heat source) and groundwater would have been a habitable environment once the system cooled below ∼120 °C. The mineral assemblage is similar to alteration minerals seen within the Martian crust from orbit, including those at Gusev and Jezero Craters. Therefore, based on our findings, and extrapolating them to the Martian crust, these sites may represent habitable environments which would call for further exploration and sample return of such hydrothermally altered igneous materials.

Martian meteorites are our only samples from Mars, thus far. Currently, there are a total of 252 individual samples originating from ≥11 ejection sites with crystallization ages varying from 4.5...

Understanding the divergent evolution of Venus and Earth is a fundamental problem in planetary science. Although Venus today has a hot, dry atmosphere, recent modeling suggests that Venus may have had a clement surface with liquid water until less than 1 billion years ago [1]. Venus today has a nearly stagnant lithosphere. However, Ishtar Terra’s folded mountain belts, 8-11 km high, morphologically resemble Tibet and the Himalaya mountains on Earth and apparently require several thousand kilometers of surface motion at some time in Venus’s past. Loss of liquid surface water increases the coefficient of friction in fault zones, favoring a transition from an early mobile lithosphere to a present-day stagnant lithosphere [2]. Solar-driven climate evolution could contribute to a prolonged epoch of water loss on Venus and may be the ultimate cause of the divergent evolution of both the climate history and the interior dynamics of Venus and Earth. In addition to being a problem of first-order importance for Solar System evolution, understanding the divergent evolution of Venus and Earth is also important for understanding the temporal and spatial distribution of habitable environments in the Solar System. Understanding the evolution of Venus is also a key test for models that interpret Earth-sized exoplanets. Testing evolutionary hypotheses requires interpreting clues that were left behind in both the isotopic composition of the Venus atmosphere and in the rock record of the Venus surface. Although several mission concepts are currently competing for possible flights to Venus, only the Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging Plus (DAVINCI+) mission [3] can examine both the atmospheric isotopic record and the rock record of Venus. DAVINCI+ is therefore a compelling choice for selection in the current NASA Discovery Program Phase A competition. DAVINCI+ includes an atmospheric entry probe and a carrier spacecraft (Figure 1). The probe measures atmospheric composition using a mass spectrometer and tunable laser spectrometer, performs descent imaging, and measures atmospheric structure. Following completion of the probe mission, the carrier spacecraft enters Venus orbit and images the Venus surface in the 1 micron atmospheric window. This payload is ideally suited for testing models of Venus evolution. Figure 1: The DAVINCI+ entry probe studies the atmosphere while imaging the Alpha Regio landing site. Afterward, the carrier probe performs infrared imaging of selected targets from orbit. The History of Water: Isotopic Record Pioneer Venus measured the D/H value of an H2SO4 cloud droplet at ~55 km as 157±30 times the terrestrial value, which was interpreted as the signature of escape of water from the Venus atmosphere [4]. Terrestrial spectroscopy produced a similar range, whereas Venus Express measured a value up to three times larger between 70-90 km [5]. The large value relative to Earth shows that Venus lost a substantial amount of water, but the large uncertainty and the lack of data below the clouds makes it difficult to quantitatively model the history of water loss [6]. DAVINCI+ will measure D/H to high precision from above the clouds down to the surface, greatly improving our ability to interpret the history of water loss on Venus. In addition, the abundance and isotopic ratios of Xe and Kr, together with the Kr/Ar and Xe/Ar ratios, which DAVINCI+ will measure with high precision, will be instrumental in revealing whether Venus and Earth formed in the same way and how their climates diverged. The History of Water: Rock Record A key but poorly answered question is the extent to which Venus has produced granitic or felsic (SiO2-rich) volcanism. Small amounts of felsic magma can be generated by lithospheric processes [7], but large amounts of felsic material requires the presence of water in the melting zone [8], as in terrestrial subduction zones. Tessera, which are regions of old, thick, highly tectonized crust, are widely accepted as the most likely location for felsic material on Venus. Venus Express observations suggest that tessera in Alpha Regio has a felsic composition [9]. DAVINCI+ will explore the presence and distribution of felsic rock in two ways. Comparison of the reflectivity at 1 micron and in panchromatic descent images at the Alpha Regio landing site will test the presence of felsic rock at patch sizes much smaller than can be observed from orbit. Descent imaging will also explore the landing zone geomorphology, and stereo topography will enable quantitative modelling of faulting and folding. Orbital imaging in the 1 micron atmospheric window will test for the presence of felsic rock in other tessera, including Tellus Regio, Fortuna Tessera, Maxwell Montes, Ovda Regio, and Thetis Regio. Our approach is similar to VIRTIS on Venus Express [9] but focuses on regions in the northern hemisphere and near the equator that were not imaged by VIRTIS. The History of Volcanism: Isotopic Record Volcanic outgassing releases radioactive decay products such as 40Ar and 4He to the atmosphere. DAVINCI+ measurements of their atmospheric abundance can be used to estimate volcanic outgassing over time. 40Ar provides an integrated record of volcanism over Venus history. Because 4He escapes from the atmosphere to space, its atmospheric abundance constrains geologically recent (last billion years) volcanism. Existing measurements of 40Ar and 4He are too imprecise to strongly constrain the volcanic history of Venus [10] but will be measured with much greater accuracy by DAVINCI+. Because DAVINCI+ will constrain the history of both water and volcanism on Venus, it will provide new insights into the feedbacks that shaped the divergent evolution of Venus and Earth. References [1] Way and Del Genio, JGR 125, e2019JE006276, 2020. [2] Weller and Kiefer, JGR 125, e2019JE005960, 2020. [3] Garvin et al., LPSC 51, abstract 2599, 2020. [4] Donahue et al., Science 216, 630-633, 1982. [5] Bertaux et al., Nature 450, 646-649, 2007. [6] Donahue et al., Venus II, 385-414, 1997. [7] Elkins-Tanton et al., JGR 112, E04S06, 2007. [8] Campbell and Taylor, GRL 10, 1061-1064, 1983. [9] Gilmore et al., Icarus 254, 350-361, 2015. [10] Namiki and Solomon, JGR 103, 3655-3677, 1998.

Directly west of the San Rafael Swell on the Colorado Plateau in the western U.S., the Jurassic Entrada Sandstone is intruded by a ~2 km long mafic dike. The dike is Miocene; however, the area is also crosscut by Laramide (~50Ma) clusters of deformation bands that are up 500 m long and up to ~3 m wide. The mafic intrusions infused the area with fluids that bleached the red sandstone directly surrounding the dike. On one side of the dike, the bleached area terminates at an adjacent deformation band set ~475 m south of the dike. Field observations suggest that the dike acted as a baffle preventing fluids from migrating further into the sandstone. Spheroidal calcite and iron (oxyhydr)oxide concretions are present in the bleached host rock, although calcite concretions (1-3 cm diameter) are present throughout the area on both sides of the deformation bands and in both red and white host rock. Iron (oxyhydr)oxide concretions (1-5 cm diameter) are limited to the uppermost bleached section between the dike and the deformation band set. Some iron concretions have solid interiors, and some have well-cemented rinds with interiors depleted of cement. Additionally, some iron concretions are nucleated on individual deformation bands that are ~2 mm wide and iron (oxyhydr)oxide cemented joint faces are also present. Thermochemical modeling shows the infiltrating Miocene fluids were CO2-bearing, but near neutral pH. The restricted location of the iron (oxyhydr)oxide concretions and relation to the calcite concretions suggest that stagnation of fluid is needed for spheroidal iron oxyhydroxide concretion formation. Calcite concretion nucleation and growth may be quicker resulting in more widespread occurrences, and/or may have preceded the Miocene fluids that infiltrated the unit. The evidence presented here shows that recently proposed models calling for calcite concretion precursors and acidic fluids for iron (oxyhydr)oxide concretion formation may not be correct.

Idunn Mons is a shield volcano located in the Imdr Regio large igneous rise, a Venusian equivalent to a hotspot geologic province on Earth. Recent studies using emissivity data from ESA's Venus Express Mission, together with experimental laboratory studies on the alteration of volcanic materials on Venus conditions, suggest that Idunn Mons is a possible site for very recent or even ongoing volcanic activity. In this work we carried out geologic mapping of Idunn Mons to characterize its materials and structures and to establish its geologic evolution. This study suggests that Idunn Mons is analogous to oceanic island volcanoes on Earth, with volcanic constructive phases that alternate with flank collapse episodes, resulting in its flat-topped summit morphology. These flank collapse events can be related to the intimate temporal and spatial relationship existing between Idunn Mons and Olapa Chasma, a rift that dominates the large igneous rise and relates to the volcano evolution, suggesting that this is not simply a candidate site for active volcanism but also for active tectonism.

Ultramafic pseudotachylytes have been regarded as earthquake fossils formed at mantle depths (i.e., >30 km). Here we show that pseudotachylytes hosted by ultramafic rocks from three localities have distinct magnetic properties. Fresh host-peridotites contain only small amounts of coarse-grained magnetite. In contrast, the ultramafic pseudotachylytes contain variable amounts of significantly finer magnetite that formed coseismically through melting. Among each locality, magnetite abundance in the pseudotachylytes ranges over several orders of magnitude (4~2000 ppm), and magnetic grain size varies considerably (from single domain to multidomain). Because the host-peridotites are compositionally similar, the pseudotachylyte magnetic properties are interpreted to primarily reflect the physical and cooling conditions prevailing during seismic slip. Further, the examination of laboratory-produced ultramafic pseudotachylytes shows that quenching does not produce superfine magnetite. We hypothesize that the magnetic properties of ultramafic pseudotachylytes are controlled by fO2 and in consequence vary systematically with depth of formation. Therefore these properties can be used to assess if the ruptures producing the earthquakes that these pseudotachylytes represent nucleated at actual mantle depths or at shallow depths during exhumation of mantle rocks.