A major upgrade to the NIRSPEC instrument at the Keck II telescope was successfully completed in time for near-infrared spectroscopic observations of comet 46P/Wirtanen during its exceptionally close flyby of Earth in 2018 December. These studies determined the abundances of several volatiles, including C₂H₂, C₂H₆, CH₃OH, NH₃, HCN, H₂CO, and H₂O. Long-slit spatial distributions of gas rotational temperature and column density are diagnostic for the presence of icy grains in the coma and understanding if different volatiles are associated with common or distinct outgassing sources. These spatial distributions suggest that C₂H₂, C₂H₆, and HCN have a common outgassing source, whereas H₂O and CH₃OH have additional, more extended sources. The synergy of these findings with observations by space missions (Rosetta and EPOXI) motivates continuing studies to address whether or not C₂H₆, C₂H₂, and HCN have a common source of release (plausibly associated with CO₂) in a larger sample of comets and whether systematic differences exist in the release of these species compared to H₂O and CH₃OH. Abundances of volatiles are reported relative to H₂O, as traditionally done, as well as C₂H₆. While not unique, the choice of C₂H₆ demonstrates the value of extending the chemical taxonomy of parent volatiles in comets toward additional compositional “baselines” and, importantly, closer integration between coma abundances and the underlying volatile associations as revealed by spatial distributions. Our findings on composition and sources of outgassing include information relevant to future evaluations of 46P/Wirtanen as a prospective spacecraft target.

Keck II望远镜对NIRSPEC仪器的重大升级已及时完成，以便在2018年12月对46P / Wirtanen彗星的异常近距离飞行中对其进行近红外光谱观察。这些研究确定几个挥发物的丰度，包括C ₂ ħ ₂，C ₂ H ^ ₆，CH ₃ OH，NH ₃，HCN，H ₂ CO和H ₂ O.长缝的气体旋转温度和列密度的空间分布诊断昏迷中是否有冰粒，并了解不同的挥发物是否与常见或不同的除气源相关。这些空间分布表明₂ H ₂，C ₂ H ₆和HCN具有共同的除气源，而H ₂ O和CH ₃ OH具有其他更广泛的排放源。这些发现与太空任务（Rosetta和EPOXI）的观测结果的协同作用，促使人们继续进行研究，以解决C ₂ H ₆，C ₂ H ₂和HCN是否具有共同的释放源（可能与CO ₂相关）。与H ₂ O和CH ₃ OH相比，更大的彗星样本以及这些物种的释放是否存在系统差异。据报道，相对于H，有大量的挥发物像传统上一样做₂ O以及C ₂ H ₆。尽管不是唯一的，但C ₂ H ₆的选择证明了将彗星母体挥发物的化学分类法扩展到其他组成“基线”的价值，并且重要的是，彗星丰度与潜在的挥发物缔合之间更紧密的整合（如空间分布所揭示）。我们关于除气成分和来源的研究结果包括与未来46P / Wirtanen作为未来航天器目标的评估有关的信息。