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Investigations of CO₂ and CO outgassing and isotopic ratios in Centaur 29P/S-W1 with JWST

Presentation #400.05 in the session Comets: Coma (Oral Presentation)

Published onOct 23, 2023
Investigations of CO₂ and CO outgassing and isotopic ratios in Centaur 29P/S-W1 with JWST

Measurements of isotopic abundances in comets provide key cosmogonic parameters to understanding the history and the origin of the material in the solar system. Isotopic fractionation is sensitive to the local conditions at the time of comet formation (e.g., temperature, radiation environment), reflecting the chemical evolution of the material from the protosolar nebula to the protoplanetary disk, before accreting into their nuclei [1]. Most isotopic abundances of carbon- and oxygen- bearing volatiles in comets to date agree with terrestrial abundances. Prior to the Rosetta mission, measurements of 12C/13C in comets were only available for HCN, CN, and C2 [2-5] and for 16O/18O in H2O [6-8]. Rosetta provided the first in-situ measurements of carbon and oxygen isotopic abundances in CO2, in Jupiter-Family Comet (JFC) 67P/Churyumov–Gerasimenko (67P) [1]. However, all previous measurements are of JFCs or long-period comets; here, we will present CO and CO2 isotopic investigations for an object showing cometary activity beyond the water ice sublimation line: Centaur 29P/Schwassmann-Wachmann 1 (here after 29P).

On 20th February 2023, we used NIRSpec IFU PRISM mode to observe Centaur 29P. The spectrum covers 0.59 to 5.29 mm, allowing simultaneous sampling of the fundamental rovibrational bands of H2O, CO2, and CO, including their less abundant isotopologues. Strong molecular signatures of CO at 4.67 mm and CO2 at 4.25 mm were detected. The extraordinary sensitivity of JWST provided the first identification of 13C16O2, 13C16O, 12C17O and 12C18O isotopes in a Centaur. To identify and characterize the isotopic signatures, we used fluorescence models and databases available in the Planetary Spectrum Generator (PSG) [9]. We will present 2D maps of detected CO and CO2 emissions, comparing our measured carbon and oxygen isotopic ratios with their in-situ values in 67P, and with terrestrial abundances.

These investigations enable exploration of primitive material from a dynamical class of small bodies that may have a formation history in the protoplanetary disk distinct from that of long-period comets, yet have not suffered the thermal processing experienced by JFCs.

References: [1] Hassig et al., 2017 A&A, 605, A50 – and ref. therein; [2] Manfroid et al. 2009 A&A 503, 613– and ref. therein; [3] Bockelee-Morvan et al. 2008, ApJ, 679, L49; [4] Biver et al. 2016 A&A 589, A78 (2016); [5] Wyckoff et al., 2000, ApJ 535, 991-999; [6] Biver et al. 2007, Planet. Space Sci., 55, 1058; [7] Bockelee-Morvan et al. 2012, A&A, 544, L15; [8] Altwegg et al. 2015 Science, 347, 1261952; [9] Villanueva et al., 2018, JQSRT, 217, 86-104.

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