During the past several decades, a shift of a substantial quantity of scientific real estate has occurred, as spacecraft data have transformed the planets from astronomical objects into geologic worlds. Mars is the current focus of planetary exploration, and NASA’s objectives for this effort are based on the theme, “follow the water.” This issue will address new discoveries from spacecraft and from Martian meteorites about where water or ice was (or is) located, and new insights into the role of water in determining the mineralogy, petrology, and geochemistry of the Martian surface.
The Mars Science Laboratory (MSL) rover Curiosity was designed and built to explore the surface of Mars and characterize its modern environment. Its primary objective was to search for ancient habitable environments. During its nominal one-Mars-year mission (23 Earth months), Curiosity drilled and scooped samples, made mineralogical, isotopic, and compositional measurements, took hundreds of thousands of images that provided geologic context for samples, and acquired millions of observations of the modern environment.Curiosity is the most advanced mobile geochemistry laboratory to have ever roved another planet, and it has been very productive. Within 8 months of landing, scientists were able to confirm mission success with evidence of an ancient habitable environment on Mars. This issue presents the range of discoveries related to the investigations of the solid materials at Gale Crater and elsewhere on Mars. [Grotzinger et al. (2015) Elements 11:19-26]