Titan in Transit: Ultraviolet Occultation Observations Reveal a Complex Atmospheric Structure. (arXiv:2006.14670v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Tribbett_P/0/1/0/all/0/1">Patrick D. Tribbett</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Robinson_T/0/1/0/all/0/1">Tyler D. Robinson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Koskinen_T/0/1/0/all/0/1">Tommi T. Koskinen</a>
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.
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.
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