Abstract: 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 1 Interpret the primary geologic processes and history that formed the Martian geologic record, with an emphasis on the role of water. Intent To 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 processes This objective is divided into five sub‐objectives that would apply at different landing sites. Characterize the essential stratigraphic, sedimentologic, and facies variations of a sequence of Martian sedimentary rocks. Intent To understand the preserved Martian sedimentary record. Samples A suite of sedimentary rocks that span the range of variation. Importance Basic inputs into the history of water, climate change, and the possibility of life Understand an ancient Martian hydrothermal system through study of its mineralization products and morphological expression. Intent To evaluate at least one potentially life‐bearing “habitable” environment Samples A suite of rocks formed and/or altered by hydrothermal fluids. Importance Identification of a potentially habitable geochemical environment with high preservation potential. Understand the rocks and minerals representative of a deep subsurface groundwater environment. Intent To evaluate definitively the role of water in the subsurface. Samples Suites of rocks/veins representing water/rock interaction in the subsurface. Importance May constitute the longest‐lived habitable environments and a key to the hydrologic cycle. Understand water/rock/atmosphere interactions at the Martian surface and how they have changed with time. Intent To constrain time‐variable factors necessary to preserve records of microbial life. Samples Regolith, paleosols, and evaporites. Importance Subaerial near‐surface processes could support and preserve microbial life. Determine the petrogenesis of Martian igneous rocks in time and space. Intent To provide definitive characterization of igneous rocks on Mars. Samples Diverse suites of ancient igneous rocks. Importance Thermochemical record of the planet and nature of the interior. Objective 2 Assess and interpret the potential biological history of Mars, including assaying returned samples for the evidence of life. Intent To 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: Assess and characterize carbon, including possible organic and pre‐biotic chemistry. Samples All samples collected as part of Objective 1. Importance Any biologic molecular scaffolding on Mars would likely be carbon‐based. Assay for the presence of biosignatures of past life at sites that hosted habitable environments and could have preserved any biosignatures. Samples All samples collected as part of Objective 1. Importance Provides the means of discovering ancient life. Assess the possibility that any life forms detected are alive, or were recently alive. Samples All samples collected as part of Objective 1. Importance Planetary protection, and arguably the most important scientific discovery possible. Objective 3 Quantitatively determine the evolutionary timeline of Mars. Intent To 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. Samples Ancient igneous rocks that bound critical stratigraphic intervals or correlate with crater‐dated surfaces. Importance Quantification of Martian geologic history. Objective 4 Constrain 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. Intent To recognize and quantify the major roles that volatiles (in the atmosphere and in the hydrosphere) play in Martian geologic and possibly biologic evolution. Samples Current atmospheric gas, ancient atmospheric gas trapped in older rocks, and minerals that equilibrated with the ancient atmosphere. Importance Key to understanding climate and environmental evolution. Objective 5 Reconstruct the processes that have affected the origin and modification of the interior, including the crust, mantle, core and the evolution of the Martian dynamo. Intent To 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. Samples Igneous, potentially magnetized rocks (both igneous and sedimentary) and impact‐generated samples. Importance Elucidate fundamental processes for comparative planetology. Objective 6 Understand and quantify the potential Martian environmental hazards to future human exploration and the terrestrial biosphere. Intent To define and mitigate an array of health risks related to the Martian environment associated with the potential future human exploration of Mars. Samples Fine‐grained dust and regolith samples. Importance Key input to planetary protection planning and astronaut health. Objective 7 Evaluate the type and distribution of in‐situ resources to support potential future Mars exploration. Intent To 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. Samples Regolith. Importance Production 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.

Abstract: Executive summary provided in lieu of abstract.

Abstract: H 2 O, CO 2 , SO 2 , O 2 , H 2 , H 2 S, HCl, chlorinated hydrocarbons, NO, and other trace gases were evolved during pyrolysis of two mudstone samples acquired by the Curiosity rover at Yellowknife Bay within Gale crater, Mars. H 2 O/OH-bearing phases included 2:1 phyllosilicate(s), bassanite, akaganeite, and amorphous materials. Thermal decomposition of carbonates and combustion of organic materials are candidate sources for the CO 2 . Concurrent evolution of O 2 and chlorinated hydrocarbons suggests the presence of oxychlorine phase(s). Sulfides are likely sources for sulfur-bearing species. Higher abundances of chlorinated hydrocarbons in the mudstone compared with Rocknest windblown materials previously analyzed by Curiosity suggest that indigenous martian or meteoritic organic carbon sources may be preserved in the mudstone; however, the carbon source for the chlorinated hydrocarbons is not definitively of martian origin.

Abstract: Sedimentary rocks examined by the Curiosity rover at Yellowknife Bay, Mars, were derived from sources that evolved from an approximately average martian crustal composition to one influenced by alkaline basalts. No evidence of chemical weathering is preserved, indicating arid, possibly cold, paleoclimates and rapid erosion and deposition. The absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low-temperature, circumneutral pH, rock-dominated aqueous conditions. Analyses of diagenetic features (including concretions, raised ridges, and fractures) at high spatial resolution indicate that they are composed of iron- and halogen-rich components, magnesium-iron-chlorine–rich components, and hydrated calcium sulfates, respectively. Composition of a cross-cutting dike-like feature is consistent with sedimentary intrusion. The geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagenetic sedimentary environments during the early history of Mars.

Abstract: The Perseverance rover landed in Jezero crater on Mars on 18 February 2021 with three scientific objectives: to explore the geologic setting of the crater, to identify ancient habitable environments and assess the possibility of past martian life, and to collect samples for potential transport to Earth for analysis in laboratories. In the 290 martian days (sols) after landing, Perseverance explored rocks of the Jezero crater floor. RATIONALE Jezero, a 45-km-diameter crater, was selected for investigation by Perseverance because orbital observations had shown that it previously contained an open-system lake, prior to ~3.5 billion years ago. Major climate change then left Mars in its current cold and dry state. On Earth, broadly similar environments of similar age to Jezero contain evidence of microbial life. Jezero crater contains a well-preserved delta, identified as a target for astrobiological investigation by the rover. Perseverance landed ~2 km away from the delta, on rocks of the crater floor. Previously proposed origins for these rocks have ranged from lake (or river) sediments to lava flows. Olivine-rich rocks identified on the crater floor, as well as in the area surrounding Jezero, have previously been attributed to a widely distributed impact melt or volcanic deposit, variably altered to carbonate. We used Perseverance to investigate the origin of the crater floor rocks and to acquire samples of them. RESULTS The Jezero crater floor consists of two geologic units: the informally named Máaz formation covers much of the crater floor and surrounds the other unit, which is informally named the Séítah formation. Máaz rocks display a range of morphologies: structureless boulders, flagstone-like outcrops, and ridges that are several meters high. The ridges expose prominent layers, ranging in thickness from a few centimeters to a few tens of centimeters. Rocks of Séítah are often tabular and strongly layered, with layer thicknesses ranging from centimeters to meters. Máaz and Séítah rocks display no outcrop or grain-scale evidence for transport by wind or water. Perseverance observations show that the Máaz rocks consist of 0.5- to 1-mm interlocking crystals of pyroxene and plagioclase. Combined with bulk chemical composition measurements, this suggests Máaz is an igneous unit that cooled slowly. In contrast, most Séítah rocks are very rich in magnesium and are dominated by densely packed 2- to 3-mm-diameter crystals of olivine, surrounded by pyroxene. These properties indicate settling and accumulation of olivine near the base of a thick magma body, such as an intrusion, lava lake, or thick lava flow. Ground-penetrating radar indicates that Séítah rocks dip beneath the Máaz formation. We hypothesize that Máaz could be the magmatic complement to the Séítah olivine-rich rocks or, alternatively, Máaz could be a series of basaltic lavas that flowed over and around the older Séítah formation. The olivines in the Séítah formation are rimmed with magnesium-iron carbonate, likely produced by interaction with CO 2 -rich water. Máaz formation rocks contain an aqueously deposited iron oxide or iron silicate alteration product. Both units commonly contain patches of bright-white salts, including sodium perchlorate and various sulfate minerals. Although both rock units have been altered by water, preservation of the original igneous minerals and the absence of aluminous clay minerals indicate that the alteration occurred under low water/rock ratio and that there was little loss of soluble species to the surroundings. It remains unclear when these aqueous processes occurred and whether they relate to the lake that once filled Jezero. The exposure of the olivine-rich Séítah rocks at the surface, the absence of lake or river sediment in the exploration area, and several nearby erosional remnant hills of delta sediment indicate that substantial crater floor erosion occurred after formation of these igneous units. Samples of both of these geologic units were collected as drill cores. The drill cores were stored in ultraclean sample tubes, for potential transport to Earth by future missions in the early 2030s. CONCLUSION The floor of Jezero crater explored by Perseverance consists of two distinct igneous units that have both experienced reactions with liquid water. Multiple rock cores were collected from these units for potential transport to Earth and analysis in terrestrial laboratories. Sample collection by Perseverance on Mars. This image mosaic was acquired by the WATSON camera on the rover’s robot arm. Rock cores were drilled from the two holes (arrow) in an igneous rock of the Máaz formation. The 6-cm-long, 1.3-cm-diameter cores were sealed into individual sample tubes and are now stored inside the rover.

Abstract: Understanding the solar system terrestrial planets is crucial for interpretation of the history and habitability of rocky exoplanets Mars' accessible geologic record extends back past 4 Ga and possibly to as long ago as 5 Myr after solar system formation Mars is key for testing theories of planetary evolution and processes that sustain habitability (or not) on rocky planets with atmospheres

Abstract: Mastcam-Z is a multispectral, stereoscopic imaging investigation on the Mars 2020 mission’s Perseverance rover. Mastcam-Z consists of a pair of focusable, 4:1 zoomable cameras that provide broadband red/green/blue and narrowband 400-1000 nm color imaging with fields of view from 25.6° × 19.2° (26 mm focal length at 283 μrad/pixel) to 6.2° × 4.6° (110 mm focal length at 67.4 μrad/pixel). The cameras can resolve (≥ 5 pixels) ∼0.7 mm features at 2 m and ∼3.3 cm features at 100 m distance. Mastcam-Z shares significant heritage with the Mastcam instruments on the Mars Science Laboratory Curiosity rover. Each Mastcam-Z camera consists of zoom, focus, and filter wheel mechanisms and a 1648 × 1214 pixel charge-coupled device detector and electronics. The two Mastcam-Z cameras are mounted with a 24.4 cm stereo baseline and 2.3° total toe-in on a camera plate ∼2 m above the surface on the rover’s Remote Sensing Mast, which provides azimuth and elevation actuation. A separate digital electronics assembly inside the rover provides power, data processing and storage, and the interface to the rover computer. Primary and secondary Mastcam-Z calibration targets mounted on the rover top deck enable tactical reflectance calibration. Mastcam-Z multispectral, stereo, and panoramic images will be used to provide detailed morphology, topography, and geologic context along the rover’s traverse; constrain mineralogic, photometric, and physical properties of surface materials; monitor and characterize atmospheric and astronomical phenomena; and document the rover’s sample extraction and caching locations. Mastcam-Z images will also provide key engineering information to support sample selection and other rover driving and tool/instrument operations decisions.

Abstract: The soils at the Opportunity site are fine-grained basaltic sands mixed with dust and sulfate-rich outcrop debris. Hematite is concentrated in spherules eroded from the strata. Ongoing saltation exhumes the spherules and their fragments, concentrating them at the surface. Spherules emerge from soils coated, perhaps from subsurface cementation, by salts. Two types of vesicular clasts may represent basaltic sand sources. Eolian ripples, armored by well-sorted hematite-rich grains, pervade Meridiani Planum. The thickness of the soil on the plain is estimated to be about a meter. The flatness and thin cover suggest that the plain may represent the original sedimentary surface.

Abstract: The Microscopic Imager on the Opportunity rover analyzed textures of soils and rocks at Meridiani Planum at a scale of 31 micrometers per pixel. The uppermost millimeter of some soils is weakly cemented, whereas other soils show little evidence of cohesion. Rock outcrops are laminated on a millimeter scale; image mosaics of cross-stratification suggest that some sediments were deposited by flowing water. Vugs in some outcrop faces are probably molds formed by dissolution of relatively soluble minerals during diagenesis. Microscopic images support the hypothesis that hematite-rich spherules observed in outcrops and soils also formed diagenetically as concretions.