Geology topics

T. B. McCord

Publications and source records attributed to T. B. McCord.

39 records · Page 3Linked to original sources

USGS1997

Organics and other molecules in the surfaces of Callisto and Ganymede

Five absorption features are reported at wavelengths of 3.4, 3.88, 4.05, 4.25, and 4.57 micrometers in the surface materials of the Galilean satellites Callisto and Ganymede from analysis of reflectance spectra returned by the Galileo mission near-infrared mapping spectrometer. Candidate materials include CO2, organic materials (such as tholins containing C???N and C-H), SO2, and compounds containing an SH-functional group; CO2, SO2, and perhaps cyanogen [(CN)2] may be present within the surface material itself as collections of a few molecules each. The spectra indicate that the primary surface constituents are water ice and hydrated minerals.

Science↗

USGS1991

Galileo infrared imaging spectroscopy measurements at Venus

During the 1990 Galileo Venus flyby, the Near Infrared Mapping Spectrometer investigated the night-side atmosphere of Venus in the spectral range 0.7 to 5.2 micrometers. Multispectral images at high spatial resolution indicate substantial cloud opacity variations in the lower cloud levels, centered at 50 kilometers altitude. Zonal and meridional winds were derived for this level and are consistent with motion of the upper branch of a Hadley cell. Northern and southern hemisphere clouds appear to be markedly different. Spectral profiles were used to derive lower atmosphere abundances of water vapor and other species.

Science↗

USGS1986

Europa: Characterization and interpretation of global spectral surface units

The Voyager global multispectral mosaic of the Galilean satellite Europa ( T. V. Johnson, L. A. Soderblom, J. A. Mosher, G. E. Danielson, A. F. Cook, and P. Kupferman, 1983, J. Geophys. Res. 88, 5789–5805 ) was analyzed to map surface units with similar optical properties ( T. B. McCord, M. L. Nelson, R. N. Clark, A. Meloy, W. Harrison, T. V. Johnson, D. L. Matson, J. A. Mosher, and L. Soderblom, 1982, Bull Amer. Astron. Soc. 14, 737 ). Color assignments in the unit map are indicative of the spectral nature of the unit. The unit maps make it possible to infer extensions of the geologic units mapped by B. K. Lucchitta and L. A. Soderblom (1982, in Satellites of Jupiter , pp. 521–555, Univ. of Arizona Press, Tucson) beyond the region covered in the high-resolution imagery. The most striking feature in the unit maps is a strong hemispheric asymmetry. It is seen most clearly in the ultraviolet/violet albedo ratio image, because the asymmetry becomes more intense as the wavelength decreases. It appears as if the surface has been darkened, most intensely in the center of the trailing hemisphere and decreasing gradually, essentially as the cosine of the angle from the antapex of motion, to a minimum in the center of the leading hemisphere. The cosine pattern suggests that the darkening is exogenic in origin and is interpreted as evidence of alteration of the surface by ion bombardment from the Jovian magnetosphere.

Icarus↗