Isotopic Ratios of Carbon and Oxygen in Titan's CO using ALMA

TL;DR

This study uses ALMA to measure isotopic ratios of carbon and oxygen in Titan's atmospheric CO, providing the most precise values to date and detecting $^{17}$O for the first time in the outer solar system.

Contribution

First spectroscopic detection of $^{17}$O in the outer solar system and precise isotopic ratio measurements in Titan's atmospheric CO.

Findings

$^{12}$C/$^{13}$C ratio = 89.9 ± 3.4

$^{16}$O/$^{18}$O ratio = 486 ± 22

$^{16}$O/$^{17}$O ratio = 2917 ± 359

Abstract

We report interferometric observations of carbon monoxide (CO) and its isotopologues in Titan's atmosphere using the Atacama Large Millimeter/submillimeter Array (ALMA). The following transitions were detected: CO (J = 1-0, 2-1, 3-2, 6-5), $^{13}$CO (J = 2-1, 3-2, 6-5), C$^{18}$O (J = 2-1, 3-2), and C$^{17}$O (J = 3-2). Molecular abundances and the vertical atmospheric temperature profile were derived by modeling the observed emission line profiles using NEMESIS, a line-by-line radiative transfer code. We present the first spectroscopic detection of $^{17}$O in the outer solar system with C$^{17}$O detected at > 8$\sigma$ confidence. The abundance of CO was determined to be 49.6 ${\pm}$ 1.8 ppm, assumed to be constant with altitude, with isotopic ratios $^{12}$C/$^{13}$C = 89.9 ${\pm}$ 3.4, $^{16}$O/$^{18}$O = 486 ${\pm}$ 22, and $^{16}$O/$^{17}$O = 2917${\pm}$359. The measurements of $^{12}$C/$^{13}$C and $^{16}$O/$^{18}$O ratios are the most precise values obtained in Titan's atmospheric CO to date. Our results are in good agreement with previous studies and suggest no significant deviations from standard terrestrial isotopic ratios.