Comet is thought to be one of the most pristine objects in the solar system. Their chemical compositions provide valuable insights of the chemical environment and evolution in the early solar system, especially formation temperatures. However, it remains uncertain whether the derived abundances of CO2 and CO relative to H2O in comets are result of their inherent compositions (nature) or have been influenced by external factors (nurture). To address this question, we concentrate on the abundances of these compounds as they vary with distance from the Sun, focusing specifically on comets known as "Dynamically new comets" (DNCs). Recently, a new method to estimate abundance ratios of H2O:CO2:CO has been established, which combines the "intensity ratio" with the "intrinsic line widths" of three [O I] lines at 557.7 nm, 630.0 and 636.4 nm. This model successfully reproduced the result of the short-period comet 21P/Giacobini-Zinner at ∼1 au from the Sun. Here we propose high-resolution optical spectroscopy of two DNCs at different heliocentric distance from our previous observations, to explore variations in the observed chemical composition in the coma and chemical evolution in the early solar system.
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