Formation and Processing of Organics in the Early Solar System

摘要: Until pristine samples can be returned from cometary nuclei, primitive meteorites represent our best source of information about organic chemistry in the early solar system. However, this material has been affected by secondary processing on asteroidal parent bodies which probably did not affect now present nuclei. Production meteoritic matter apparently involved following sequence events: Molecule formation a variety reaction pathways dense interstellar clouds; Condensation those molecules onto refractory grains; Irradiation organic-rich interstellar-grain mantles producing range molecular fragments and free radicals; Inclusion grains into protosolar nebula with probable heating at least some grain during passage through shock wave bounding accretion disc; Agglomeration residual locally produced nebular condensates asteroid-sized planetesimals; Heating planetesimals decay extinct radionuclides; Melting ice to produce liquid water within bodies; Reaction molecules, radicals each other aqueous environment, possibly catalysed mineral Loss volatiles space yielding partially hydrated lithology containing complex suite molecules; generate kerogen-like complex; Mixing heated unheated yield observed. Properties believed consistent scenario include: Systematic decrease abundance increasing C number homologous series characterisable Complete structural diversity series; Predominance branched-chain isomers; Considerable isotopic variability among material; Substantial deuterium enrichment all fractions; Some fractions significantly enriched nitrogen-15; Modest excesses L-enantiomers racemisation-resistant but no general enantiomeric preference. Despite much speculation possible role Fischer-Tropsch catalytic hydrogenation CO production nebula, convincing evidence for such found meteorites. A similarity between organics Miller-Urey discharge synthesis may reflect involvement common intermediates rather than operation electric discharges Meteoritic constitutes useful, exact, guide what we shall find situ analytical sample-return missions