The most volatile elements and compounds: organic matter, noble gases, and ices

Abstract

Overview The most volatile constituents of meteorites, small bodies, and planets are highly depleted in rocky bodies compared to the solar composition. In this chapter we first consider the sometimes bewilderingly complex molecules composed of carbon and hydrogen, often with other elements like oxygen, nitrogen, and sulfur (organic compounds). Following an introduction to terminology and structures, we focus on the organic matter in chondritic meteorites – the only extraterrestrial organic materials currently available for detailed analysis. This material appears to be a mixture of compounds inherited from the interstellar medium and synthesized within solar system bodies. Next, we look at noble gases, which do not condense as solids and thus are strongly depleted in meteorites and planets, relative to solar system abundances. The concentrations and isotopic compositions of noble gases in meteorites and planetary atmospheres provide unique perspectives on processes occurring in the early solar system and during planetary differentiation. Finally, we briefly consider ices, surprisingly abundant phases that dominate the outer solar system. Ices trapped noble gases and provided sites for the formation of simple organic compounds in space. Volatility In several previous chapters, we have discussed element volatility. Here we focus on some of the most volatile constituents in meteorites – organic compounds, noble gases, and ices. Each of these actually constitutes a voluminous subject of its own in cosmochemistry, and we can only provide overviews of these interesting components.