Evidence for condensed-phase methane enhancement over Xanadu on Titan

TL;DR

This study provides evidence of condensed-phase methane precipitation near Xanadu on Titan, using multi-night observations and radiative transfer models to distinguish atmospheric effects from surface artifacts.

Contribution

It introduces a novel observational and modeling approach to detect and confirm condensed-phase methane near Titan's surface, specifically over Xanadu.

Findings

Condensed-phase methane opacity is observed near Xanadu.

Multiple observations support precipitation as the cause.

Models rule out surface artifacts as the primary explanation.

Abstract

We present evidence for condensed phase methane precipitation near Xanadu using nine nights of observations from the SINFONI integral-field spectrograph at the Very Large Telescope and imaging analysis with empirical surface subtraction. Radiative transfer models are used to support the imaging technique by simulating the spectrometer datacubes and testing for variations in both the surface reflectivity spectrum and atmospheric opacity. We use the models and observations together to argue against artifacts that may arise in the image analysis. High phase angle observations from Cassini/VIMS are used to test against surface scattering artifacts that may be confused with sources of atmospheric opacity. Although changes in the surface reflectivity spectrum can reproduce observations from a particular viewing geometry on a given night, multiple observations are best modeled by condensed-phase methane opacity near the surface. These observations and modeling indicate that the condensed-phase methane opacity observed with this technique occurs predominantly near Xanadu and is most likely due to precipitation.