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B. J. Buratti, M. D. Hicks, K. A. Tryka, R. L. Newburn, Jr. (Jet Propulsion Laboratory, California Institute of Technology)
Historical observations of the color and albedo of Triton show that volatile transport has occurred on its surface during the last 4 decades (Buratti et al., Icarus 110, 1994). Over this time period, its integral spectrum has exhibited a steady increase in the relative albedo of the blue and ultraviolet regions. This "blueing" suggests a seasonal global deposition of a volatile that is bright into the ultraviolet, or alternately, the sublimation of a red volatile. In spite of this secular trend to the color of Triton, two independent observers measured a very red spectrum for Triton in 1977 (Bell et al., B.A.A.S. 11, 1979; Cruikshank et al. Icarus 40, 1979). The juxtaposition of these observations next to "nominal" spectra obtained within the same year (Degewij et al. Icarus 44, 1980; Franz, Icarus 45, 1981), suggests Triton may exhibit short term spectral changes.
Observations obtained in October 1997 with the 200-inch Hale telescope at Palomar Mountain Observatory and the double spectrograph show a similarly red spectrum for Triton. A lower resolution BVRI spectrum obtained in May 1998 shows that Triton's spectral properties were again "nominal". Because the Bond albedo of Triton is so high, even a very small change in color would cause a large change in the Bond albedo and a concomitant change in temperature. Recent observations of a warming trend on Triton (Elliot et al. Nature, 1998) may be due in part to short lived spectral changes that are perhaps triggered by geologic events.
This work was performed under contract to NASA.