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Identifying Clouds and the Vertical Abundances of Haze and Methane on Titan with Applications to Exoplanets

Presentation #632.03 in the session Other - Observational.

Published onApr 03, 2024
Identifying Clouds and the Vertical Abundances of Haze and Methane on Titan with Applications to Exoplanets

Saturn’s largest moon, Titan, is an excellent candidate for observational analogs of exoplanets. Titan hosts a thick atmosphere with complex organic chemistry resulting from the UV photolysis of methane and nitrogen, resulting in the formation of complex aerosols that obscure Titan’s surface. Haze and clouds are expected to occur on exoplanets, potentially limiting the ability to probe the full atmosphere. Our observations demonstrate a technique for not only identifying haze and methane clouds, but also their vertical distributions (see Thieberger et al, this conference). We will present observations centered across various longitudes in order to get an integrated picture of these vertical distributions and to look for global scale and temporal differences. We use the Lowell Discovery Telescope (LDT) EXtreme PREcision Spectrometer (EXPRES) to study Titan’s spectrum from ~0.4 - 0.75-µm at resolution R~135,000. This slope is set by absorption and scattering of UV and visible light by aerosols, and will lead to constraints on the composition and vertical abundance of hazes in Titan’s atmosphere. The high resolution also allows identification of narrow features attributed to specific molecules yet to be determined. Observations with EXPRES are sensitive to Titan’s middle and upper atmosphere; we also observe with LDT’s Near-Infrared High-Throughput Spectrograph (NIHTS) which is low-resolution (R~200), covering 0.86-2.4 µm. Using both instruments allows access to the methane windows that can see down to Titan’s surface, permitting us to complete the vertical abundance retrievals through Titan’s entire atmosphere. Also, by comparing the brightness at specific wavelengths, we can monitor for any changes that might indicate cloud formation. Data from EXPRES show many features attributed to reflected sunlight, but one challenge that arises from the high spectral resolution is the issue of dividing by a reference star. Typical Solar System observations use a G2 star as a solar analog. Due to variations in composition and rotation rates between these stars and the Sun, they are not compatible with our observations. Thus we have started using the Lowell Observatory Solar Telescope (LOST) which collects EXPRES spectra of the Sun daily to divide by (see Llama et al, this conference). Our results demonstrate that probing various depths of the atmosphere is possible for exoplanets.

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