  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
the depletions of other molecules, especially C2H2 and HCN. 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.
