VSTAR Modelling of the Infrared Spectrum of Uranus

TL;DR

This paper models Uranus's infrared spectrum using VSTAR to analyze atmospheric composition and cloud structure, aiming to determine the D/H ratio, with a focus on methane absorption data accuracy.

Contribution

It introduces a VSTAR-based modeling approach incorporating recent methane line data to improve atmospheric analysis of Uranus.

Findings

Model accurately reproduces Uranus's infrared spectrum in the 0.1-11 bar range.

Identifies methane absorption as dominant in the spectrum, highlighting data quality limitations.

Provides a framework for future D/H ratio determination from high-resolution spectra.

Abstract

We modelled the H-band spectrum obtained with the Infrared Imaging Spectrograph (IRIS2) at the Anglo-Australian Telescope in order to infer the cloud structure and composition of the atmosphere of the planet between 0.1 and 11 bar. Such modelling can be used to derive the D/H ratio in the atmosphere of Uranus, which is an important diagnostic of the conditions in early history of the planetary formation. We describe here our modelling technique based on the Versatile Software for Transfer of Atmospheric Radiation (VSTAR) (Bailey2012a). Since the infrared spectrum of Uranus is dominated by absorption from methane, the accuracy of the models is limited largely by the quality of the low temperature, methane line databases used. Our modelling includes the latest laboratory line data for methane described in Bailey (2011). The parameters of this model will be applied in the future to model our observations of GNIRS high resolution spectra of Uranus and derive the D/H ratio in the 1.58 micron window based on absorption in the deuterated methane band in this region.