Oxygen on Ganymede: Laboratory Studies
R. A. Vidal,
*
D. Bahr,
R. A. Baragiola,
M. Peters
To test proposals for the origin of oxygen absorption bands in the
visible reflectance spectrum of Ganymede, the reflectance of condensed
films of pure oxygen (O2) and O2-water mixtures
and the evolution of O2 from the films as a function of
temperature were determined. Absorption band shapes and positions for
oxygen at 26 kelvin were similar to those reported for Ganymede,
whereas those for the mixtures were slightly shifted. The band
intensity dropped by more than two orders of magnitude when the ice
mixture was warmed to 100 kelvin, although about 20 percent of the
O2 remained trapped in the ice, which suggested that at
these temperatures O2 molecules dissolve in the ice rather
than aggregate in clusters or bubbles. The experiments suggest that the
absorption bands in Ganymede's spectrum were not produced in the
relatively warm surface of the satellite but in a much colder source.
Solid O2 may exist in a cold subsurface layer or in an
atmospheric haze.
R. A. Vidal, D. Bahr, R. A. Baragiola, Laboratory for Atomic and
Surface Physics, University of Virginia, Thornton Hall,
Charlottesville, VA 22901, USA.
M. Peters, School of Medicine, Laboratory of Physics, Teikyo
University, Ohtsuka 359, Hachioji-shi, Tokyo 192, Japan.
*
Present address: Instituto de Tecnología Quíonica,
Güemes 3450, 3000 Santa Fé, Argentina.
To whom correspondence should be addressed. E-mail:
raul{at}virginia.edu
