The microwave spectra of the asteroids Pallas, Vesta, and Hygiea

Journal Article · Sat Jul 01 04:00:00 EDT 1989 · Astronomical Journal; (USA)

DOI:https://doi.org/10.1086/115150· OSTI ID:5397731

Johnston, K J; Lamphear, E J; Webster, Jr, W J; Lowman, Jr, P D; Seidelmann, P K ^[1]

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1. E. O. Hulburt Center for Space Research, Washington, DC (USA)

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. 21 refs.

• OSTI ID: 5397731
• Journal Information: Astronomical Journal; (USA), Journal Name: Astronomical Journal; (USA) Vol. 98; ISSN 0004-6256; ISSN ANJOA
• Country of Publication: United States
• Language: English

Related Subjects

640107* -- Astrophysics & Cosmology-- Planetary Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ASTEROIDS
BLACKBODY RADIATION
BRIGHTNESS
CHEMICAL COMPOSITION
ELECTROMAGNETIC RADIATION
EMISSION SPECTRA
EMISSIVITY
HYDROGEN COMPOUNDS
ICE
INTERFEROMETRY
MICROWAVE SPECTRA
MOTION
OPTICAL PROPERTIES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
RADIATIONS
ROTATION
SPECTRA
SURFACE PROPERTIES
SURFACES
WATER