New Developments in Inner Solar Nebula Chemistry

The molecular cloud material which became the asteroids, meteorites and inner planets was extensively processed in the inner solar nebula. The chemical complexity of the most ancient meteorites attests to the highly nonequilibrium nature of the chemistry in this region, particularly regarding the volatile elements. Theoretical models describing the time evolution of the temperature and density profiles of protoplanetary accretion disks have recently become available. Such models provide a realistic framework within which to study, for instance, the effects of lightning and surface-catalyzed (gas-grain) reactions in the inner nebula. Here, we show that the latter would have been most efficient during the meteorite-forming epoch of the nebula, at the present position of the asteroid belt.