The evolution of scientific goals for Mars exploration and future prospects

Mars is currently in the spotlight of solar system exploration and planetary science study. The scientific questions of Mars are closely integrated with big enigmas of the solar system, highlighting the centrality of Mars in understanding the formation and evolution of our solar system. After nearly six decades of exploration, Mars is easily the most studied planet in the solar system besides Earth, with a profusion of research across space environment, atmosphere, surface-subsurface compositions, topography and structure, impact history, glaciers and cryosphere, climate change, and internal structure. Martian meteorite and laboratory simulation studies (experimental and numerical) are also developing rapidly. Key discoveries in the past 20 years include evidence of past and current aqueous activity, geological environment diversity, modern geological processes, methane emissions and preserved organics, atmospheric composition and evolution, current and recent climate change, gravity fields and surface radiation environments, etc. Such scientific achievements, underpinned by peer-reviewed research goals developed by the planetary community, in turn shape future goals and targets. We review how the Mars exploration goals and targets (e.g., life, climate, geology, preparation for human exploration) have evolved in the past 20 years, and show priorities and focii for future international Mars exploration. For example, the Mars exploration strategy evolved thematically from “follow the water” to “understand Mars as a system”, “understand the long-term evolution of habitability on Mars”, and “exploration by humans on Mars”. In the next 10−20 years, Mars exploration will further characterize the internal structure of Mars, start a new era of life detection, and return samples from Mars and its satellites. China’s first Mars mission will contribute to the international Mars science community with an orbiter and a rover exploring the northern lowlands with advanced payloads. New findings such as the structure of the Martian critical zone (i.e., vertical zone of interaction between the atmosphere and crust with immediate relevance for habitability), local and global characteristics of the residual crustal magnetism, volcanic-geothermal evolution and the cyclicity of glaciations will clarify the still poorly known provenance and evolution of the topographic dichotomy. Hypotheses such as the formation of the global dichotomy by an oblique impact or an ancient ocean-sustaining climate may be tested and constrained. Internationally planned sample-return from Mars and its satellites, combined with study of Martian meteorites, experimental and numerical simulation of Martian processes, and study of terrestrial analog sites and samples will build absolute geochronology of Mars and constrain the timing and duration of critical events, such as cessation of the global magnetic field, quiescence of volcanism across the Noachian-Hesperian temporal boundary, transition to a single-plate planet, aqueous and sedimentary processes, and global climate change.