Distributions of H2O and CO2 ices on Ariel, Umbriel, Titania, and Oberon from IRTF/SpeX observations

TL;DR

This study uses spectral observations to map the distribution of H2O and CO2 ices on Uranian satellites, revealing new detections of CO2 ice and hemispherical asymmetries in ice distribution.

Contribution

First detection of CO2 ice on Umbriel and Titania, with detailed mapping of ice distributions on Uranian satellites using spectral data.

Findings

CO2 ice detected on Umbriel and Titania, absent on Oberon

CO2 ice most abundant on trailing hemispheres

H2O ice bands deeper on leading hemispheres of Ariel, Umbriel, Titania

Abstract

We present 0.8 to 2.4 micron spectral observations of uranian satellites, obtained at IRTF/SpeX on 17 nights during 2001-2005. The spectra reveal for the first time the presence of CO2 ice on the surfaces of Umbriel and Titania, by means of 3 narrow absorption bands near 2 microns. Several additional, weaker CO2 ice absorptions have also been detected. No CO2 absorption is seen in Oberon spectra, and the strengths of the CO2 ice bands decline with planetocentric distance from Ariel through Titania. We use the CO2 absorptions to map the longitudinal distribution of CO2 ice on Ariel, Umbriel, and Titania, showing that it is most abundant on their trailing hemispheres. We also examine H2O ice absorptions in the spectra, finding deeper H2O bands on the leading hemispheres of Ariel, Umbriel, and Titania, but the opposite pattern on Oberon. Potential mechanisms to produce the observed longitudinal and planetocentric distributions of the two ices are considered.