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Constraining the Variability of Haze and Methane on Titan

Presentation #208.02 in the session Titan I: Atmosphere (Oral Presentation)

Published onOct 23, 2023
Constraining the Variability of Haze and Methane on Titan

Titan hosts a thick atmosphere with complex organic chemistry resulting from the UV photolysis of methane, forming complex aerosols that obscure Titan’s surface. Further, methane acts as the primary absorber in the near-IR, resulting in narrow “windows” that probe to intermediate depths of Titan’s atmosphere allowing vertical retrievals of methane and haze abundance. We will present observations from the Lowell Discovery Telescope (LDT) centered across various longitudes in order to get an integrated global picture of these vertical distributions and to look for global scale and temporal differences in these distributions. These observations provide critical insights into the chemical pathways in the upper atmosphere and help constrain the rate of UV photolysis, and by extension the loss-rate of methane, which remains an open question in the Titan community. We use LDT’s EXtreme PREcision Spectrometer (EXPRES) observations to study the spectral features of Titan visible spectrum from ~0.4 - 0.75 µm at a resolution of R ~ 137,500. This slope is set by absorption of UV and visible light by aerosols, and will lead to constraints on the composition and vertical abundance of hazes in Titan’s atmosphere, similar to the photometric analysis conducted with HST. In addition, measuring the shape and strength of the methane absorption feature at 0.62 µm at high resolution will allow for sensitive constraints on the vertical distribution of methane in Titan’s atmosphere, similar to studies conducted with Keck. To complement the visible wavelengths, we also observe with LDT’s Near-Infrared High-Throughput Spectrograph (NIHTS) which is a low-resolution (R ~ 200) near-infrared (NIR) prism spectrograph, covering 0.86 - 2.4 µm. NIHTS provides access to the five methane windows (at 0.938, 1.1, 1.3, 1.6, and 2.0 µm) that can see down to Titan’s surface, permitting us to complete the vertical abundance retrievals through Titan’s entire atmosphere. Data from EXPRES shows many features attributed to reflected sunlight, but also the larger methane features expected at ~0.62 and 0.7 µm. The high resolution will allow for broad features such as UV absorption of hazes, as well as narrow features attributed to specific molecules yet to be determined. Preliminary analysis of NIHTS data shows good signal-to-noise that will allow for correlation with the EXPRES data and will permit studies of the longitudinal variability in Titan’s methane abundance.

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