2008ApJ...680L..61B

We report measurements of eight native (i.e., released directly from the comet nucleus) volatiles (H₂O, HCN, CH₄, C₂H₂, C₂H₆, CO, H₂CO, and CH₃OH) in comet 8P/Tuttle using NIRSPEC at Keck 2. Comet Tuttle reveals a truly unusual composition, distinct from that of any comet observed to date at infrared wavelengths. The prominent enrichment of methanol relative to water contrasts with the depletions of other molecules, especially C₂H₂, HCN, and H₂CO. We suggest that the nucleus of 8P/Tuttle may contain two cometesimals characterized by distinct volatile composition. The relative abundances C₂/CN, C₂/OH, and CN/OH in 8P/Tuttle (measured at optical/near-UV wavelengths) differ substantially from the mixing ratios of their potential parents (C₂H₂/HCN, C₂H₂/H₂O, and HCN/H₂O) found in this work. Based on this comparison, our results do not support C₂H₂ and HCN being the principal precursors for respectively C₂ and CN in Tuttle. The peculiar native composition observed in 8P/Tuttle (compared to other comets) provides new strong evidence for chemical diversity in the volatile materials stored in comet nuclei. We discuss the implications of this diversity for expected variations in the deuterium enrichment of water among comets.