Abstract Near–Earth asteroids and comets, collectively the near-Earth objects (NEOs), represent a large population of minor planetary bodies whose orbits lie mostly within the zone between Venus and Mars. Many of these objects cross Earth’s orbit, providing relatively easy access from Earth for manned or robotic sampling and exploration missions with fewer propulsion requirements than trips to the Moon or to Mars. This chapter provides a review of NEOs in the context of supporting, through in-situ resource utilization, an active and expanding space exploration and resource development program capable of becoming self-funding and supporting a solar systemwide expansion program. The NEO compositions range from highly metallic asteroids composed predominantly of iron, nickel, and cobalt to cometlike objects composed of frozen water and gases of various compositions. The NEOs are the most easily accessible objects in near–Earth space, and they are numerous. As of January 2011, a total of 7872 NEOs had been identified. The number of NEOs with diameters greater than 1 km (>0.6 mi) reached 1269 by June 2012. Moreover, 1176 have been identified as potentially hazardous Earth impactors by the National Aeronautics and Space Administration’s Near–Earth Object Program, approaching Earth to within 0.05 astronomical units or approximately 7,480,000 km (4,647,860 mi). The value of NEOs for space exploration may far exceed the immediate scientific information that they provide on the origin of the solar system: NEOs have the potential to provide fuel for rockets; oxygen and life support materials for explorers; valuable materials and metals for construction in space; and critical, strategic, and highly valuable materials for Earth. Water ice derived from extinct NEO comets or water–rich asteroids can be refined to provide liquid oxygen and liquid hydrogen for rocket fuel and the oxygen necessary for life support. Carbonaceous chondrites contain kerogenlike compounds that can support the immense carbon chemistry developed for our petroleum industry, and metallic asteroids contain platinum–group and rare–earth elements that have been conservatively valued in the hundreds of billions to trillions of dollars if they were made available in Earth markets. These resources are accessible using existing rockets and boosters, but these existing systems and technologies are nearly 50 years out–of–date. Active space exploration and development programs require highly efficient nuclear rockets and space–based nuclear power systems to reduce launch costs to economically tolerable numbers and to provide the heavy–lift capacity and highly efficient rocket engines for crew health and safety and minimum duration missions. Once flight launches are outside Earth’s atmosphere, the NEOs can provide nearly unlimited resources for further exploration.

ABSTRACT Many of the minerals observed or inferred to occur in the sediments and sedimentary rocks of Mars, from a variety of Mars-mission spacecraft data, also occur in Martian meteorites. Even Martian meteorites recovered after some exposure to terrestrial weathering can preserve preterrestrial evaporite minerals and useful information about aqueous alteration on Mars, but the textures and textural contexts of such minerals must be examined carefully to distinguish preterrestrial evaporite minerals from occurrences of similar minerals redistributed or formed by terrestrial processes. Textural analysis using terrestrial microscopy provides strong and compelling evidence for preterrestrial aqueous alteration products in a number of Martian meteorites. Occurrences of corroded primary rock-forming minerals and alteration products in meteorites from Mars cover a range of ages of mineral–water interaction, from ca. 3.9 Ga (approximately mid-Noachian), through one or more episodes after ca. 1.3 Ga (approximately mid–late Amazonian), through the last half billion years (late Amazonian alteration in young shergottites), to quite recent. These occurrences record broadly similar aqueous corrosion processes and formation of soluble weathering products over a broad range of times in the paleoenvironmental history of the surface of Mars. Many of the same minerals (smectite-group clay minerals, Ca-sulfates, Mg-sulfates, and the K-Fe–sulfate jarosite) have been identified both in the Martian meteorites and from remote sensing of the Martian surface. This suggests that both kinds of samples—Martian meteorites and Mars’ surface rocks, regolith, and soils—were altered under broadly similar conditions. Temporarily and locally occurring but likely stagnant aqueous solutions reacted quickly with basaltic/mafic/ultramafic minerals at low water–rock ratios. Solutes released by primary mineral weathering precipitated locally on Mars as cation-rich clays and evaporite minerals, rather than being leached away, as on Earth. The main secondary host minerals for Fe differ between Martian meteorites and Mars’ surface materials. In Martian meteorites, sideritic–ankeritic carbonate is the predominant secondary host mineral for Fe, whereas in Mars’ surface materials, ferric oxides and ferric sulfates are the predominant secondary host minerals for Fe. Differences in the initial compositions of the altering solutions are implied, with carbonate/bicarbonate dominating in the solutions that altered Martian meteorites, and sulfate dominating the solutions that altered most Mars’surface materials. During impact on and ejection from Mars, Martian meteorites may have been exhumed from depths sufficient to have isolated them from large quantities of Mars’surface solutions. Pre-ejection weathering of the basaltic rocks occurred in grain-boundary fracture microenvironments at high pH values in aqueous solutions buffered by reactions with basalt minerals.