Reflectance Spectroscopy of Icy Surfaces

Abstract

Reflectance spectroscopy provides much of our knowledge about the compositions and physical properties of planetary, satellite, and asteroid surfaces. Two complementary aspects of reflectance spectroscopy are exploited in studies of icy satellites and other bodies. One approach, spectroscopic analysis, derives information about surface composition from variations in the intensity of reflected light with wavelength (usually from ultraviolet to near-infrared wavelengths, about 0.3 — 4.0μm); the other, photometric analysis, estimates surface physical characteristics from the way reflected light varies with illumination and viewing geometry. The foundation of spectroscopic analysis is that many minerals selectively absorb light at specific, diagnostic wavelengths. By comparing absorption bands in spectra of icy satellites to those seen in laboratory spectra of candidate regolith-forming materials, we now know that H2O is the dominant icy constituent in the regoliths of the icy satellites of Jupiter, Saturn, and Uranus and is present on the surface of Pluto’s moon, Charon. Ices of N2, CH4, and CO cover the surfaces of Triton and Pluto (CO2 ice is also present on Triton). Excellent current reviews describing spectroscopic analysis of surface ices on outer solar system bodies are published elsewhere (e.g. Roush et al. 1995, Cruik-shank and Brown 1993) as well as in this book (see chapters by Cruikshank et al).