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 μ m, R ∼ 60–127) and short wavelength–high resolution (SH; 9.89–19.51 μ m, R ∼ 600) channels 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 μ m wavelength range observed by the SH channel but impacted by higher noise levels in the CIRS observations. We use the SH data to provide estimated haze extinction cross sections for the 16.67–17.54 μ m range that are missing in previous studies. We conclude by identifying spectral features in the 16.35–19.35 μ m wavelength range that could be analyzed further through upcoming James Webb Space Telescope Cycle 1 observations with the Mid-Infrared Instrument (5.0–28.3 μ m, R ∼ 1500–3500). We also highlight gaps in the 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.

Keywords

• Titan
• Radiative transfer
• Natural satellite atmospheres
• Saturnian satellites
• Transmission spectroscopy
• Infrared astronomy