Carbon Chemistry of Apollo 14 Size-fractionated Fines

TOTAL carbon measurements of crystalline lunar rocks returned by the Apollo missions have revealed only low concentrations of carbon (10-50 p.p.m.)1-3. The breccias and fines, however, have, in general, higher carbon concentrations (up to 200 p.p.m.). This carbon is more concentrated in the finer fractions1 and is correlated with the noble gas content of the solar wind2. It has been postulated that most of the carbon associated with the fines and breccia originated in the solar wind1,4. The dissolution of lunar material in mineral acids and direct pyrolysis have been the principal techniques used to reveal the nature of this lunar carbon; in particular, experiments5-8 on Apollo 12 samples using deuterated reagents have shown the presence of indigenous CH4 and C2H6. The CD4, C2D4 and C2D6 also released are evidence for the presence of hydrolysable carbides in the samples. The yields of these gases from several samples have been shown6,7 to correlate with various parameters related to exposure to the solar wind. Shallow etching of fines with NaOD released more than 60% of the CH4 found by complete dissolution7, indicating that most of the CH4 is in the surface of the grains and may therefore be connected with implantation by the solar wind5.