(A) Selected IR reflectance spectra of a 200 ML ethane film atop a 1,000 ML water ice at 55 K, recorded over time, showing minimal spectral change in ethane absorption features (3,366 nm, 3,400 nm, and 3,473 nm) following 3.5 hours (210 minutes) of annealing. (B) At 60 K, the depth of these absorption features decreases over this time period owing to desorption of the ethane layer. The large absorption band spanning ∼ 2,800-3,300 nm corresponds to water ice.