SOLAR-SYSTEM OBSERVATIONS BY THE WISCONSIN ULTRAVIOLET PHOTOPOLARIMETER EXPERIMENT .2. THE FIRST LINEAR ULTRAVIOLET SPECTROPOLARIMETRY OF IO

The Wisconsin Ultraviolet Photopolarimeter Experiment (WUPPE) observed Io during the Astro-l mission on 1990 December 7 and during the Astro -2 mission on 1995 March 4, 9, and 16 in the wavelength range 2100-310 0 Angstrom with a resolution of 100 Angstrom. The albedo measurements are consistent with about 25% of the surface being covered by an SO2 f rost. Polarimetric differences between the March 9 and 16 observations (orbital phase 288 degrees and 268 degrees, respectively) are interpr eted as arising due to the rotational effect of two polarized regions on Io which are either associated with the volcanic site Pele or Hepha estus Patera and Viracocha Patera. (C) 1997 American Astronomical Soci ety.