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Inferring the CO 2 Abundance in Comet 45P/Honda-Mrkos-Pajdušáková from [O i] Observations: Implications for the Source of Icy Grains in Cometary Comae

2024; Institute of Physics; Volume: 5; Issue: 2 Linguagem: Inglês

10.3847/psj/ad1935

2632-3338

Mikayla R. Huffman, Adam McKay, A. L. Cochran,

Planetary Science and Exploration

Abstract The study of cometary composition is important for understanding our solar system's early evolutionary processes. Carbon dioxide (CO 2 ) is a common hypervolatile in comets that can drive activity but is more difficult to study than other hypervolatiles owing to severe telluric absorption. CO 2 can only be directly observed from space-borne assets. Therefore, a proxy is needed to measure CO 2 abundances in comets using ground-based observations. The flux ratio of the [O i ] λ 5577 line to the sum of the [O i ] λ 6300 and [O i ] λ 6364 lines (hereafter referred to as the [O i ] line ratio) has, with some success, been used in the past as such a proxy. We present an [O i ] line ratio analysis of comet 45P/Honda-Mrkos-Pajdušáková (HMP), using data obtained with the Tull Coudé Spectrograph on the 2.7 m Harlan J. Smith Telescope at McDonald Observatory, taken from UT 2017 February 21–23, when the comet was at heliocentric distances of 1.12–1.15 au. HMP is a hyperactive Jupiter-family comet (JFC). Icy grains driven out by CO 2 sublimation have been proposed as a driver of hyperactivity, but the CO 2 abundance of HMP has not been measured. From our [O i ] line ratio measurements, we find a CO 2 /H 2 O ratio for HMP of 22.9% ± 1.4%. We compare the CO 2 /H 2 O ratios to the active fractions of the nine comets (including HMP) in the literature that have data for both values. We find no correlation. These findings imply that CO 2 sublimation driving out icy grains is not the only factor influencing active fractions for cometary nuclei.