Larry A. Lebofsky

Saturn's rings: Spectral reflectivity and compositional implications

Abstract A photometric study of the rings of Saturn was carried out during the 1969 apparition. A reflection spectrum of the A and B rings was obtained for the spectral region 0.3–1.05 μ. The reflectivity for both rings decreases sharply toward blue and ultraviolet wavelengths. A comparison of the ring reflection spectrum with spectra for other solar system objects shows that the ring curve most closely resembles the curve for the Galilean satellite J1. The ring spectrum lacks distinctive absorption features found in lunar, Martian, and Vesta spectra in the 0.3–1.1 μ region. Absorption features characteristic of water frost have been found recently in the 1.25–2.5 μ region, but the decrease in reflectivity of the rings toward shorter wavelengths indicates that material other than pure water frost also must be present. A physical mixture of frost and silicates seems to be unlikely as ring material. Frost-covered silicates and mixtures of frosts with other compounds, perhaps modified by ultraviolet or high-energy particle radiation, remain possible ring constituents.

Laboratory reflection spectra for the determination of chemical composition of icy bodies

Abstract The visible (0.3 to 1.03 μm) spectral reflectances of H2O, NH3, H2S, and NH4HS frosts and mixtures of these frosts and their uv irradiated products have been measured. These spectra are compared with the spectra of the Galilean satellites of Jupiter, Saturns rings and Saturns satellites to place limits on their surface composition.

Comet Bennett 1969 i - Narrow-band filter photometry 0.3 to 1.1 microns

During March of 1970, narrow-band photometric observations of the head of Comet Bennett, 1969 i were made. Nineteen interference filters ( AA O.3 ) were used to scan the spectrum from 0.34 iL to 1.1 . From 0.4 to 1.1 the flux measured was very similar to the solar continuum indicating that the light in this region of the spectrum is primarily reflected or scattered solar radiation. The gray character of the reflection spectrum is similar to the continuum reported for comets 1967 n and 1968 c (Gebel 1970) but different from the red color of the tails of 1956 h and 1957 d (Liller 1960). A strong excess in the comets flux over the solar continuum was noted for wavelengths shorter than 0.4 this probably results from CN emission. Key words: comet - narrow-band photometry - Comet Bennett 1969 i

Chapter 26 – Main-Belt Asteroids

Asteroids (or more properly, minor planets) are small, naturally formed solid bodies that orbit the Sun, are airless, and show no detectable outflow of gas or dust. Although asteroids share many of the characteristics of planets (Sun-centered orbits, seemingly solid bodies), the primary distinction is that they are simply much smaller than the known planets or dwarf planets. Similarly, the distinction between asteroids and comets is also based on their observational qualities rather than any inherent difference in physical properties or composition. This chapter discusses locations, orbits, physical composition, and various other aspects of asteroids.