The Microwave Spectra of the Asteroids Pallas, Vesta, and Hygiea

view Abstract Citations (19) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The microwave spectra of the asteroids Pallas, Vesta, and Hygiea Johnston, K. J. ; Lamphear, E. J. ; Webster, W. J. ; Lowman, P. D. ; Seidelmann, P. K. ; Kaplan, G. H. ; Wade, C. M. ; Hobbs, R. W. Abstract Microwave observations of Pallas, Vesta, and Hygiea at 2 and 6 cm wavelength yield brightness temperatures that are much lower than would be expected for a rapidly rotating blackbody. An analysis of the wavelength dependence of the observed brightness temperatures shows that, as was found for Ceres, these asteroids may be covered by a layer of material with the physical properties of finely divided dust. Models with layer depths of greater than 6 cm (Pallas), 6 cm (Vesta), and 8 cm (Hygiea) were found to represent well the variation in emissivity at radio wavelengths. The properties of the underlying layer are not well constrained by the microwave observations. It does appear that the real part of the dielectric vector for the substrate is similar to that of basaltic rock. Major compositional changes, if any, must take place at depths greater than about 10 cm. No evidence for water ice was found. Disk-resolved observations of the 2-cm emission of Vesta yield physical dimensions consistent with the recently published speckle-interferometry results. Publication: The Astronomical Journal Pub Date: July 1989 DOI: 10.1086/115150 Bibcode: 1989AJ.....98..335J Keywords: Black Body Radiation; Brightness Temperature; Microwave Spectra; Vesta Asteroid; Ceres Asteroid; Emission Spectra; Rotating Bodies; Speckle Interferometry; ASTEROIDS; MICROWAVE METHODS; SPECTRA; PALLAS; VESTA; HYGIEA; BRIGHTNESS; WAVELENGTHS; SURFACE; COMPOSITION; DUST; DEPTH; LAYERS; EMISSIVITY; COMPARISONS; ASTRONOMY; EARTH-BASED OBSERVATIONS; DIELECTRIC PROPERTIES; DATA; SUBSURFACE; REGOLITH; EMISSIONS; Astronomy; Asteroids full text sources ADS |