The Peculiar Volatile Composition of Comet 8P/Tuttle: A Contact Binary of Chemically Distinct Cometesimals?

Abstract

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.

Accepted for Astrophysical Journal Letters

References in corpus (3)

• The Size Distribution of Trans-Neptunian Bodies
• Hot Organic Molecules Toward a Young Low-Mass Star: A Look at Inner Disk Chemistry
• Warm HCN, C2H2, and CO in the disk of GV Tau

Cited by in corpus (11)

• Elemental and molecular abundances in comet 67P/Churyumov-Gerasimenko
• The Composition of Comets
• Comet C/2004 Q2 (MACHHOLZ): Parent Volatiles, a Search for Deuterated Methane, and Constraint on the CH4 Spin Temperature
• Cometary diversity and cometary families
• Forbidden oxygen lines at various nucleocentric distances in comets
• Water in the Near IR spectrum of Comet 8P/Tuttle
• Chandra Observations of Comets 8P/Tuttle and 17P/Holmes during Solar Minimum
• The Distribution, Excitation and Formation of Cometary Molecules: Methanol, Methyl Cyanide and Ethylene Glycol
• Swift UVOT Grism Spectroscopy of Comets: A First Application to C/2007 N3 (Lulin)
• Earth-based detection of the millimetric thermal emission of the nucleus of comet 8P/Tuttle
• Spitzer Space Telescope observations of bilobate comet 8P/Tuttle