Titan in Transit: Ultraviolet Occultation Observations Reveal a Complex Atmospheric Structure


Altitude- and wavelength-dependent transmission data for Titan’s atmosphere from Cassini flyby T41 I. An altitude of 0 km corresponds to Titan’s average surface radius (2575 km), and darker colors indicate lower transmission.

Transit spectroscopy is a key tool for exoplanet atmospheric characterization. However, transit spectrum observations can be limited by aerosol extinction when gas opacities are weak.

The ultraviolet wavelength range contains a variety of strong molecular and atomic features, potentially enabling gas species detection even when atmospheric hazes are present. To understand the interplay between aerosol extinction and ultraviolet molecular opacities, we investigate transmission through the atmosphere of Saturn's moon Titan during an occultation observed with the Ultraviolet Imaging Spectrometer (UVIS) aboard NASA's Cassini orbiter.

We analyze the derived ultraviolet transit spectrum of Titan using atmospheric retrieval models that both include and exclude treatments for hazes. Our retrieved atmospheric properties, namely the gas column densities, are consistent with previous studies analyzing UVIS occultation data. Using the Bayesian Information Criterion, we demonstrate that haze parameterizations were unnecessary to fit the data despite apparent opacity due to multiple detached haze layers in the underlying occultation data. Our work indicates that continued characterization of exoplanets in the ultraviolet wavelength regime can provide novel atmospheric constraints even if transit spectra are dominated by haze extinction at longer wavelengths.

Patrick D. Tribbett, Tyler D. Robinson, Tommi T. Koskinen

Comments: 18 pages, 11 figures, submitted to AAS journals; comments and feedback welcome
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2006.14670 [astro-ph.EP] (or arXiv:2006.14670v1 [astro-ph.EP] for this version)
Submission history
From: Patrick Tribbett
[v1] Thu, 25 Jun 2020 19:26:32 UTC (5,546 KB)
https://arxiv.org/abs/2006.14670
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