CVF SPECTROPHOTOMETRY OF PLUTO - CORRELATION OF COMPOSITION WITH ALBEDO

Time-resolved spectrophotometry of the Pluto-Charon system was obtained on 6 nigths in March and April of 1988. The observations include about one-third of the 6.4-day lightcurve, centered around minimum light, and span the wavelength region from 0.96 to 2.65 μm. The spectra reveal night-to-night variations in depths of methane absorptions throughout this region. Band depths vary such that their equivalent width is least near minimum light. One obvious interpretation is that dark regions on the planet are depleted in methane relative to bright areas, at least for the hemisphere observed. Our results are consistent with the observations of M.W. Buie and U. Fink (1987, Icarus 70, 483-498) but in conflict with those of S.R. Sawyer (1989, Bull. Amer. Astron. Sci. 21, 986, Abstract). The near-infrared spectrum of Pluto appears to be dominated by surface frost; atmospheric methane contributes much less to the overall spectral signature. We see evidence that Pluto's dark equatorial regions tend to be redder than those of more moderate albedo. © 1991.