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Carbon, central to astrobiology, shaped the development of the dwarf planet Ceres, a water-rich protoplanet explored by NASA’s Dawn mission. As a candidate ocean world, Ceres has the potential to provide new insights into prebiotic chemistry and habitability. This chapter reviews observations of carbon and organic matter on Ceres by Dawn and Earth-based telescopes. The observations are placed in context with astrophysical processes that produced organic matter in nebular materials from which Ceres grew. We consider mechanisms for destruction and synthesis of organic matter with changing hydrothermal conditions within Ceres’ interior. This is supported by studies of Ceres’ closest meteorite analogs, the aqueously altered carbonaceous chondrites, and halite crystals containing organic matter that may have formed within Ceres. Ultraviolet-, infrared-, and nuclear-spectroscopy show that Ceres’ surface contains a mixture of carbonates and organic matter in concentrations higher than the meteorite analogs. Ceres carbon-rich surface results from a combination of impacts and complex processes that occurred within Ceres’ interior, including low-temperature aqueous alteration, ice-rock fractionation, and modification of the accreted carbon species during serpentinization. This chapter reviews the current state of knowledge about carbon on Ceres, including sources of carbon and organics, parent body processes, remote sensing observations, and their interpretation.
This chapter provides a brief review of missions using X-ray, gamma-ray, and neutron spectroscopy to determine the chemical composition of planetary surfaces. This chapter presents the history of planetary radiation measurements, including significant discoveries. Summary tables with links to the archived data provide a resource for readers interested in working in this field. Upcoming missions and possible future directions are described.
Neutrons, gamma rays, and X-rays are used to measure the subsurface elemental composition of Solar System bodies, providing insights into their formation and evolution. Neutrons and gamma rays are highly penetrating particles made by the steady bombardment of the regolith of airless bodies by galactic cosmic rays. Gamma rays are also made by the decay of natural radioelements. The escaping radiation can be detected in close-proximity orbits and analyzed to determine subsurface elemental composition to depths of a few decimeters. Because the radiation sensors have nearly omnidirectional response, spatial resolution depends on orbital altitude. X-ray fluorescence is induced by solar X-rays. Consequently, X-ray spectroscopy is most useful for studies of objects in the inner Solar System. Characteristic elemental X-rays are made within the uppermost ~100 micrometers of the surface. The suite of elements analyzed overlaps that of nuclear spectroscopy, providing complementary geochemical information. Because X-rays are easily collimated, relatively high spatial resolution measurements are possible. This chapter presents the fundamentals of neutron, gamma-ray, and X-ray production, transport, and detection along with an overview of the measurement principles, including modeling, analysis, and mapping methods.