Oxygen on Ganymede: Laboratory Simulations
R. A. Baragiola, R. A. Vidal, D. A. Bahr (University of Virginia), M. Peters (Teikyo University)
To test proposals for the origin of oxygen absorption bands
in the visible reflectance spectrum of Ganymede we measured
the reflectance of condensed films of pure and -water
mixtures and the evolution of from the films as a
function of temperature. Absorption band shapes and positions
for oxygen at 26 K are similar to those reported for Ganymede
whereas those for the mixtures are slightly shifted. The band
intensity drops by more than two orders of magnitude when the
ice mixture is warmed to 100 K, although about 20% of the
remains trapped in the ice, suggesting that at these temperatures
molecules dissolve in the ice rather than aggregate in
clusters or bubbles. The experiments suggest that the absorption
bands in Ganymede�s spectrum are not produced in the relatively
warm surface of the satellite but in a much colder source.
We discuss the possibility that the solid exists in a cold
subsurface layer or in an atmospheric haze.