Oxygen on Ganymede: laboratory studies

R. A. VIDAL; D. BAHR; R. A. BARAGIOLA; M. PETERS

SCIENCE

American Association for the Advancement of Science

Año: 1997 vol. 276 p. 1839 - 1842

0036-8075

To test proposals for the origin of oxygen absorption bands in the visible reflectancespectrum of Ganymede, the reflectance of condensed films of pure oxygen (O2) andO2-water mixtures and the evolution of O2 from the films as a function of temperaturewere determined. Absorption band shapes and positions for oxygen at 26 kelvin weresimilar to those reported for Ganymede, whereas those for the mixtures were slightlyshifted. The band intensity dropped by more than two orders of magnitude when the icemixture was warmed to 100 kelvin, although about 20 percent of the O2 remained trappedin the ice, which suggested that at these temperatures O2 molecules dissolve in the icerather than aggregate in clusters or bubbles. The experiments suggest that the absorptionbands in Ganymede’s spectrum were not produced in the relatively warm surfaceof the satellite but in a much colder source. Solid O2 may exist in a cold subsurface layeror in an atmospheric haze.