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Northwest Africa (NWA) 2737, one of the only three discovered Martian chassignites, provides critical constraints on the evolution of the Martian mantle and crust. Because of chassignites' cumulative nature, they contain abundant melt inclusions (MI). MI are small droplets of melts trapped by crystals during the cooling of magma. They are critical to the study of pre‐eruptive parental magma compositions, and thus, provide snapshots of the composition and evolution of Martian magmatic systems. Here, we present fractional crystallization models using parental magma composition calculated from NWA 2737 melt inclusions as starting compositions. We used the thermodynamic modeling software MELTS to model fractional crystallization of NWA 2737 parental magma compositions with a wide range of parameters (pressure, water content, oxygen fugacity). Our models show that the felsic compositions recently analyzed at the Martian surface in Gale crater, especially Sparkle and Angmaat, the two rocks thought to be analogous to the earliest continental crust on Earth, can be obtained by fractional crystallization of chassignite‐like parental melts. Our results suggest a link between the processes that resulted in chassignites and the rocks analyzed in situ at Gale crater. To assess the possible scenarios for Martian magma migration and storage processes, we compared chassignites to terrestrial analogs formed via various mechanisms and proposed two mechanisms that may explain the intrusive and effusive rocks found in situ at Gale crater: (1) emplacement and fractionation in a closed‐system crustal reservoir and (2) eruption of mafic to intermediate lavas of a relatively open system subject to constant replenishment. [ABSTRACT FROM AUTHOR]

The presence and accessibility of a sub‐ice‐surface saline ocean at Enceladus, together with geothermal activity and a rocky core, make it a compelling location to conduct further, in‐depth, astrobiological investigations to probe for organic molecules indicative of extraterrestrial life. Cryovolcanic plumes in the south polar region of Enceladus enable the use of remote in situ sampling and analysis techniques. However, efficient plume sampling and the transportation of captured organic materials to an organic analyzer present unique challenges for an Enceladus mission. A systematic study, accelerating organic ice‐particle simulants into soft inert metal targets at velocities ranging 0.5–3.0 km s−1, was carried out using a light gas gun to explore the efficacy of a plume capture instrument. Capture efficiency varied for different metal targets as a function of impact velocity and particle size. Importantly, organic chemical compounds remained chemically intact in particles captured at speeds up to ~2 km s−1. Calibration plots relating the velocity, crater, and particle diameter were established to facilitate future ice‐particle impact experiments where the size of individual ice particles is unknown. [ABSTRACT FROM AUTHOR]

Executive Summary: Return of samples from the surface of Mars has been a goal of the international Mars science community for many years. Affirmation by NASA and ESA of the importance of Mars exploration led the agencies to establish the international MSR Objectives and Samples Team (iMOST). The purpose of the team is to re‐evaluate and update the sample‐related science and engineering objectives of a Mars Sample Return (MSR) campaign. The iMOST team has also undertaken to define the measurements and the types of samples that can best address the objectives. Seven objectives have been defined for MSR, traceable through two decades of previously published international priorities. The first two objectives are further divided into sub‐objectives. Within the main part of the report, the importance to science and/or engineering of each objective is described, critical measurements that would address the objectives are specified, and the kinds of samples that would be most likely to carry key information are identified. These seven objectives provide a framework for demonstrating how the first set of returned Martian samples would impact future Martian science and exploration. They also have implications for how analogous investigations might be conducted for samples returned by future missions from other solar system bodies, especially those that may harbor biologically relevant or sensitive material, such as Ocean Worlds (Europa, Enceladus, Titan) and others. Summary of Objectives and Sub‐Objectives for MSR Identified by iMOST: Objective 1Interpret the primary geologic processes and history that formed the Martian geologic record, with an emphasis on the role of water.IntentTo investigate the geologic environment(s) represented at the Mars 2020 landing site, provide definitive geologic context for collected samples, and detail any characteristics that might relate to past biologic processesThis objective is divided into five sub‐objectives that would apply at different landing sites. 1.1Characterize the essential stratigraphic, sedimentologic, and facies variations of a sequence of Martian sedimentary rocks.IntentTo understand the preserved Martian sedimentary record.SamplesA suite of sedimentary rocks that span the range of variation.ImportanceBasic inputs into the history of water, climate change, and the possibility of life1.2Understand an ancient Martian hydrothermal system through study of its mineralization products and morphological expression.IntentTo evaluate at least one potentially life‐bearing "habitable" environmentSamplesA suite of rocks formed and/or altered by hydrothermal fluids.ImportanceIdentification of a potentially habitable geochemical environment with high preservation potential.1.3Understand the rocks and minerals representative of a deep subsurface groundwater environment.IntentTo evaluate definitively the role of water in the subsurface.SamplesSuites of rocks/veins representing water/rock interaction in the subsurface.ImportanceMay constitute the longest‐lived habitable environments and a key to the hydrologic cycle.1.4Understand water/rock/atmosphere interactions at the Martian surface and how they have changed with time.IntentTo constrain time‐variable factors necessary to preserve records of microbial life.SamplesRegolith, paleosols, and evaporites.ImportanceSubaerial near‐surface processes could support and preserve microbial life.1.5Determine the petrogenesis of Martian igneous rocks in time and space.IntentTo provide definitive characterization of igneous rocks on Mars.SamplesDiverse suites of ancient igneous rocks.ImportanceThermochemical record of the planet and nature of the interior.Objective 2Assess and interpret the potential biological history of Mars, including assaying returned samples for the evidence of life.IntentTo investigate the nature and extent of Martian habitability, the conditions and processes that supported or challenged life, how different environments might have influenced the preservation of biosignatures and created nonbiological "mimics," and to look for biosignatures of past or present life.This objective has three sub‐objectives: 2.1Assess and characterize carbon, including possible organic and pre‐biotic chemistry.SamplesAll samples collected as part of Objective 1.ImportanceAny biologic molecular scaffolding on Mars would likely be carbon‐based.2.2Assay for the presence of biosignatures of past life at sites that hosted habitable environments and could have preserved any biosignatures.SamplesAll samples collected as part of Objective 1.ImportanceProvides the means of discovering ancient life.2.3Assess the possibility that any life forms detected are alive, or were recently alive.SamplesAll samples collected as part of Objective 1.ImportancePlanetary protection, and arguably the most important scientific discovery possible.Objective 3Quantitatively determine the evolutionary timeline of Mars.IntentTo provide a radioisotope‐based time scale for major events, including magmatic, tectonic, fluvial, and impact events, and the formation of major sedimentary deposits and geomorphological features.SamplesAncient igneous rocks that bound critical stratigraphic intervals or correlate with crater‐dated surfaces.ImportanceQuantification of Martian geologic history.Objective 4Constrain the inventory of Martian volatiles as a function of geologic time and determine the ways in which these volatiles have interacted with Mars as a geologic system.IntentTo recognize and quantify the major roles that volatiles (in the atmosphere and in the hydrosphere) play in Martian geologic and possibly biologic evolution.SamplesCurrent atmospheric gas, ancient atmospheric gas trapped in older rocks, and minerals that equilibrated with the ancient atmosphere.ImportanceKey to understanding climate and environmental evolution.Objective 5Reconstruct the processes that have affected the origin and modification of the interior, including the crust, mantle, core and the evolution of the Martian dynamo.IntentTo quantify processes that have shaped the planet's crust and underlying structure, including planetary differentiation, core segregation and state of the magnetic dynamo, and cratering.SamplesIgneous, potentially magnetized rocks (both igneous and sedimentary) and impact‐generated samples.ImportanceElucidate fundamental processes for comparative planetology.Objective 6Understand and quantify the potential Martian environmental hazards to future human exploration and the terrestrial biosphere.IntentTo define and mitigate an array of health risks related to the Martian environment associated with the potential future human exploration of Mars.SamplesFine‐grained dust and regolith samples.ImportanceKey input to planetary protection planning and astronaut health.Objective 7Evaluate the type and distribution of in‐situ resources to support potential future Mars exploration.IntentTo quantify the potential for obtaining Martian resources, including use of Martian materials as a source of water for human consumption, fuel production, building fabrication, and agriculture.SamplesRegolith.ImportanceProduction of simulants that will facilitate long‐term human presence on Mars. Summary of iMOST Findings: Several specific findings were identified during the iMOST study. While they are not explicit recommendations, we suggest that they should serve as guidelines for future decision making regarding planning of potential future MSR missions. The samples to be collected by the Mars 2020 (M‐2020) rover will be of sufficient size and quality to address and solve a wide variety of scientific questions.Samples, by definition, are a statistical representation of a larger entity. Our ability to interpret the source geologic units and processes by studying sample sub sets is highly dependent on the quality of the sample context. In the case of the M‐2020 samples, the context is expected to be excellent, and at multiple scales. (A) Regional and planetary context will be established by the on‐going work of the multi‐agency fleet of Mars orbiters. (B) Local context will be established at field area‐ to outcrop‐ to hand sample‐ to hand lens scale using the instruments carried by M‐2020.A significant fraction of the value of the MSR sample collection would come from its organization into sample suites, which are small groupings of samples designed to represent key aspects of geologic or geochemical variation.If the Mars 2020 rover acquires a scientifically well‐chosen set of samples, with sufficient geological diversity, and if those samples were returned to Earth, then major progress can be expected on all seven of the objectives proposed in this study, regardless of the final choice of landing site. The specifics of which parts of Objective 1 could be achieved would be different at each of the final three candidate landing sites, but some combination of critically important progress could be made at any of them.An aspect of the search for evidence of life is that we do not know in advance how evidence for Martian life would be preserved in the geologic record.  In order for the returned samples to be most useful for both understanding geologic processes (Objective 1) and the search for life (Objective 2), the sample collection should contain BOTH typical and unusual samples from the rock units explored.  This consideration should be incorporated into sample selection and the design of the suites. The retrieval missions of a MSR campaign should (1) minimize stray magnetic fields to which the samples would be exposed and carry a magnetic witness plate to record exposure, (2) collect and return atmospheric gas sample(s), and (3) collect additional dust and/or regolith sample mass if possible. 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The investigation into whether Mars contains signatures of past or present life is of great interest to science and society. Amino acids and nucleobases are compounds that are essential for all known life on Earth and are excellent target molecules in the search for potential Martian biomarkers or prebiotic chemistry. Martian meteorites represent the only samples from Mars that can be studied directly in the laboratory on Earth. Here, we analyzed the amino acid and nucleobase content of the shergottite Roberts Massif (RBT) 04262 using liquid chromatography-mass spectrometry. We did not detect any nucleobases above our detection limit in formic acid extracts; however, we did measure a suite of protein and nonprotein amino acids in hot-water extracts with high relative abundances of β-alanine and γ-amino- n-butyric acid. The presence of only low (to absent) levels of several proteinogenic amino acids and a lack of nucleobases suggest that this meteorite fragment is fairly uncontaminated with respect to these common biological compounds. The distribution of straight-chained amine-terminal n-ω-amino acids in RBT 04262 resembled those previously measured in thermally altered carbonaceous meteorites (Burton et al. 2012; Chan et al. 2012). A carbon isotope ratio of −24‰ ± 6‰ for β-alanine in RBT 04262 is in the range of reduced organic carbon previously measured in Martian meteorites (Steele et al. 2012). The presence of n-ω-amino acids may be due to a high temperature Fischer-Tropsch-type synthesis during igneous processing on Mars or impact ejection of the meteorites from Mars, but more experimental data are needed to support these hypotheses. [ABSTRACT FROM AUTHOR]

One of the most productive and well-sampled dense collection areas for meteorites on Earth is the 'Franconia strewn field' in Mohave County, Arizona, which since 2002 has yielded hundreds of meteorites in an ellipsoidal area approximately 5 × 16 km across. Based on petrographic, mineral-chemical, and terrestrial age data, we conclude that among 14 meteorites examined, there are at least 6 and possibly 8 distinct meteorites represented, which fell over a period of approximately 0-20 kyr ago. These include equilibrated H-chondrites such as Franconia (H5) and Buck Mountains ( BM) 001 (H6); H3-6 breccias such as Buck Mountains Wash and BM 004; and L6 chondrites such as BM 002 and BM 003 (which may be paired), Palo Verde Mine, and BM 005. To confidently pair such meteorites often requires thorough petrographic examination, mineral-chemical analyses, and terrestrial ages. We estimate that 50 ± 10% of the larger specimens in this area are paired, yielding a relatively high value of approximately 2.3-2.9 distinct meteorites km−2. The meteorite flux estimated for Franconia area is higher than the flux inferred from contemporary fireball data for larger masses. We suggest that one large H3-6 meteoroid fell in the area, most likely that of Buck Mountains Wash approximately 4 kyr ago, which produced an elliptical strewn field with masses generally increasing toward one end, and which raised the meteorite productivity in the recovery area. [ABSTRACT FROM AUTHOR]