S22A0062

Comet is thought to be one of pristine objects in the solar system. These chemical compositions restrict the chemical environment and evolution in the early solar system, especially formation temperatures. It is unclear whether the derived abundances of CO₂ and CO with respect to H₂O of comets with eccentricity of e<1.0 are nature or nurture. Hence, we focus on a comet firstly approaching the inner solar system from the Oort Cloud, so called a "dynamically new comet" (DNC). Recently, our group has established new method to estimate abundance ratios of H₂O:CO₂:CO simultaneously using the intensity ratio with the intrinsic line width of three forbidden emission lines of oxygen atoms. This method is based on theoretical simulation of the excess kinetic energy of oxygen atoms given by photodissociation reactions of H₂O, CO₂ and CO in the coma. We confirmed that this method can reproduce the result of comet 21P/Giacobini-Zinner at ∼1 au from the Sun well. We propose high-resolution optical spectroscopy of the DNC C/2017 K2 (PanSTARRS) during its inbound orbit to explore chemical evolution in the early solar system from abundance ratio of H₂O:CO₂:CO of the comet.

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