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

TL;DR

This study reveals that comet 8P/Tuttle has a unique volatile composition, with significant methanol enrichment and other molecular depletions, suggesting it may contain two chemically distinct cometesimals and highlighting chemical diversity in comet nuclei.

Contribution

The paper provides the first detailed infrared measurements of native volatiles in 8P/Tuttle, revealing its unusual composition and proposing the presence of two distinct cometesimals within its nucleus.

Findings

8P/Tuttle shows a unique volatile profile with high methanol and low C2H2, HCN.

The composition suggests the nucleus may contain two chemically distinct cometesimals.

Results challenge previous assumptions about precursor molecules for C2 and CN in comets.

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.