Mars exploration motivates the search for extraterrestrial life, the development of space technologies, and the design of human missions and habitations. Here, we seek new insights and pose unresolved questions relating to the natural history of Mars, habitability, robotic and human exploration, planetary protection, and the impacts on human society. Key observations and findings include: –high escape rates of early Mars' atmosphere, including loss of water, impact present-day habitability; –putative fossils on Mars will likely be ambiguous biomarkers for life; –microbial contamination resulting from human habitation is unavoidable; and –based on Mars' current planetary protection category, robotic payload(s) should characterize the local martian environment for any life-forms prior to human habitation. Some of the outstanding questions are: –which interpretation of the hemispheric dichotomy of the planet is correct; –to what degree did deep-penetrating faults transport subsurface liquids to Mars' surface; –in what abundance are carbonates formed by atmospheric processes; –what properties of martian meteorites could be used to constrain their source locations; –the origin(s) of organic macromolecules; –was/is Mars inhabited; –how can missions designed to uncover microbial activity in the subsurface eliminate potential false positives caused by microbial contaminants from Earth; –how can we ensure that humans and microbes form a stable and benign biosphere; and –should humans relate to putative extraterrestrial life from a biocentric viewpoint (preservation of all biology), or anthropocentric viewpoint of expanding habitation of space? Studies of Mars' evolution can shed light on the habitability of extrasolar planets. In addition, Mars exploration can drive future policy developments and confirm (or put into question) the feasibility and/or extent of human habitability of space.

The morphology, molecular composition, and distribution of organic matter (OM) were investigated in a suite of CR chondrites to better constrain its hydrothermal evolution. Multiple focused ion beam sections were extracted from the matrices of seven CR chondrites. Scanning transmission X‐ray microscopy and transmission electron microscopy reveal OM ubiquitously distributed across the CR matrices. OM mainly occurs as either discrete submicron rounded or irregularly shaped vein‐like particles. Two spectral populations of organic particles were identified by carbon K‐edge X‐ray absorption near edge structure (XANES): the most abundant one, similar to insoluble organic matter (IOM) residues, contains aromatic, carbonyl, and carboxylic groups. The second population is more aromatic‐rich and lacks a distinctive carbonyl peak. An additional, ubiquitous organic component occurs associated with amorphous silicates and phyllosilicates. Less aromatic but aliphatic‐ and carboxylic‐rich, this diffuse OM is interpreted as the result of the redistribution of organic compounds by aqueous fluids. The most altered CR1 GRO 95577 contains a more mature OM and highly aliphatic‐ and carboxylic‐rich diffuse OM. This evolution, from the CR2s to the CR1, is comparable to that of terrestrial gas shale maturation involving cracking reactions, releasing bitumen‐like, aliphatic‐, and carboxylic‐rich compounds, and aromatic residues. Our observations support the accretion of soluble OM and its later polymerization to IOM, as well as the maturation of IOM and its partial oxidation, releasing mobile compounds. The differences in GRO 95577 are clearly attributable to the hydrothermal episode(s), but the relative role of water and temperature on the evolution of OM remains elusive.

The history of mare volcanism critically informs the thermal evolution of the Moon. However, young volcanic eruptions are poorly constrained by remote observations and limited samples, hindering an understanding of mare eruption flux over time. The Chang’e-5 mission returned the youngest lunar basalts thus far, offering a window into the Moon’s late-stage evolution. Here, we investigate the mineralogy and geochemistry of 42 olivine and pyroxene crystals from the Chang’e-5 basalts. We find that almost all of them are normally zoned, suggesting limited magma recharge or shallow-level assimilation. Most olivine grains record a short timescale of cooling. Thermal modeling used to estimate the thickness and volume of the volcanism sampled by Chang’e-5 reveals enhanced magmatic flux ~2 billion years ago, suggesting that while overall lunar volcanic activity may decrease over time, episodic eruptions at the final stage could exhibit above average eruptive fluxes, thus revising models of lunar thermal evolution.

The recent return of samples from asteroid 162173 Ryugu provides a first insight into early Solar System prebiotic evolution from known planetary bodies. Ryugu’s samples are CI chondrite-like, rich in water and organic material, and primarily composed of phyllosilicate. This phyllosilicate surrounds micron to submicron macromolecular organic particles known as insoluble organic matter. Using advanced microscopy techniques on Hayabusa-2 samples, we find that aqueous alteration on Ryugu produced organic particles richer in aromatics compared to less altered carbonaceous chondrites. This challenges the view that aromatic-rich organic matter formed pre-accretion. Additionally, widespread diffuse organic material occurs in phyllosilicate more aliphatic-, carboxylic-rich, and aromatic-poor than the discrete organic particles, likely preserving the soluble organic material. Some organic particles evolved to encapsulate phyllosilicate, indicating that aqueous alteration on Ryugu led to the containment of soluble organic matter within these particles. Earth therefore has been, and continues to be, delivered micron-sized polymeric organic objects containing biologically relevant molecules.