Spitzer IRS Observations of Titan as a Precursor to JWST MIRI Observations

Abstract

In this work we present, for the first time, infrared spectra of Titan from the Spitzer Space Telescope ($2004-2009$). The data are from both the short wavelength-low resolution (SL, $5.13-14.29\mu \mathrm{m},R\sim 60-127$) and short wavelength-high resolution channels (SH, $9.89-19.51\mu \mathrm{m},R\sim 600$) showing the emissions of CH${}_4$, C${}_2$H${}_2$, C${}_2$H${}_4$, C${}_2$H${}_6$, C${}_3$H${}_4$, C${}_3$H${}_6$, C${}_3$H${}_8$, C${}_4$H${}_2$, HCN, HC${}_3$N, and CO${}_2$. We compare the results obtained for Titan from Spitzer to those of the Cassini Composite Infrared Spectrometer (CIRS) for the same time period, focusing on the $16.35-19.35\mu \mathrm{m}$ wavelength range observed by the SH channel but impacted by higher noise levels in CIRS observations. We use the SH data to provide estimated haze extinction cross-sections for the $16.67-17.54\mu \mathrm{m}$ range that are missing in previous studies. We conclude by identifying spectral features in the $16.35-19.35\mu \mathrm{m}$ wavelength range, including two prominent emission features at 16.39 and $17.35\mu \mathrm{m}$, that could be analyzed further through upcoming James Webb Space Telescope Cycle 1 observations with the Mid-Infrared Instrument ($5.0-28.3\mu \mathrm{m},R\sim 1500-3500$). We also highlight gaps in current spectroscopic knowledge of molecular bands, including candidate trace species such as C${}_{60}$ and detected trace species such as C${}_3$H${}_6$, that could be addressed by theoretical and laboratory study.

Accepted to Planetary Science Journal April 28, 2023

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• The Atmosphere of Titan in Late Northern Summer from JWST and Keck Observations
• Photochemical Haze Formation on Titan and Uranus: A Comparative Review