  The surfaces of the large Uranian satellites are characterized by a mixture
of H2O ice and a dark, potentially carbon-rich, constituent, along with CO2
ice. At the mean heliocentric distance of the Uranian system, native CO2 ice
should be removed on timescales shorter than the age of the Solar System.
Consequently, the detected CO2 ice might be actively produced. Analogous to
irradiation of icy moons in the Jupiter and Saturn systems, we hypothesize that
charged particles caught in Uranus' magnetic field bombard the surfaces of the
Uranian satellites, driving a radiolytic CO2 production cycle. To test this
hypothesis, we investigated the distribution of CO2 ice by analyzing
near-infrared (NIR) spectra of these moons, gathered using the SpeX
spectrograph at NASA's Infrared Telescope Facility (IRTF) (2000 - 2013).
Additionally, we made spectrophotometric measurements using images gathered by
the Infrared Array Camera (IRAC) onboard the Spitzer Space Telescope (2003 -
2005). We find that the detected CO2 ice is primarily on the trailing
hemispheres of the satellites closest to Uranus, consistent with other
observations of these moons. Our band parameter analysis indicates that the
detected CO2 ice is pure and segregated from other constituents. Our
spectrophotometric analysis indicates that IRAC is not sensitive to the CO2 ice
detected by SpeX, potentially because CO2 is retained beneath a thin surface
layer dominated by H2O ice that is opaque to photons over IRAC wavelengths.
Thus, our combined SpeX and IRAC analyses suggest that the near-surfaces (i.e.,
top few 100 microns) of the Uranian satellites are compositionally stratified.
We briefly compare the spectral characteristics of the CO2 ice detected on the
Uranian moons to icy satellites elsewhere, and we also consider the most likely
drivers of the observed distribution of CO2 ice.
