Prof. Patrick Irwin

Abstract:

<jats:title>Abstract</jats:title> <jats:p>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 <jats:italic>μ</jats:italic>m, <jats:italic>R</jats:italic> ∼ 60–127) and short wavelength–high resolution (SH; 9.89–19.51 <jats:italic>μ</jats:italic>m, <jats:italic>R</jats:italic> ∼ 600) channels showing the emissions of CH<jats:sub>4</jats:sub>, C<jats:sub>2</jats:sub>H<jats:sub>2</jats:sub>, C<jats:sub>2</jats:sub>H<jats:sub>4</jats:sub>, C<jats:sub>2</jats:sub>H<jats:sub>6</jats:sub>, C<jats:sub>3</jats:sub>H<jats:sub>4</jats:sub>, C<jats:sub>3</jats:sub>H<jats:sub>6</jats:sub>, C<jats:sub>3</jats:sub>H<jats:sub>8</jats:sub>, C<jats:sub>4</jats:sub>H<jats:sub>2</jats:sub>, HCN, HC<jats:sub>3</jats:sub>N, and CO<jats:sub>2</jats:sub>. 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 <jats:italic>μ</jats:italic>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 <jats:italic>μ</jats:italic>m range that are missing in previous studies. We conclude by identifying spectral features in the 16.35–19.35 <jats:italic>μ</jats:italic>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 <jats:italic>μ</jats:italic>m, <jats:italic>R</jats:italic> ∼ 1500–3500). We also highlight gaps in the current spectroscopic knowledge of molecular bands, including candidate trace species such as C<jats:sub>60</jats:sub> and detected trace species such as C<jats:sub>3</jats:sub>H<jats:sub>6</jats:sub>, that could be addressed by theoretical and laboratory study.</jats:p>

Abstract:

The study of isotopic ratios in planetary atmospheres gives an insight into the formation history and evolution of these objects. The more we can constrain these ratios, the better we can understand the history and future of our solar system. To help in this endeavour, we used Infrared Space Observatory Short Wavelength Spectrometer (ISO/SWS) Jupiter observations in the 793–1500 cm (Formula presented.) region together with the Nonlinear Optimal Estimator for MultivariatE Spectral analySIS (NEMESIS) radiative transfer suite to retrieve the temperature–pressure profile and the chemical abundances for various chemical species. We also used the 1500–2499 cm (Formula presented.) region to determine the cloud and aerosol structure of the upper troposphere. We obtained a best-fit simulated spectrum with (Formula presented.) for the 793–1500 cm (Formula presented.) region and (Formula presented.) for the 1500–2499 cm (Formula presented.) region. From the retrieved methane abundances, we obtained, within a 1 (Formula presented.) uncertainty, a (Formula presented.) C/ (Formula presented.) C ratio of 84 ± 27 and a D/H ratio of (3.5 ± 0.6) × 10 (Formula presented.), and these ratios are consistent with other published results from the literature.