Engineering topics

Zuber, M. T.

Publications and source records attributed to Zuber, M. T..

94 records · Page 6

NASA NTRS1984

A geometric analysis of surface deformation - Implications for the tectonic evolution of Ganymede

The identification of various types of surface deformation of Ganymede by a geometric study of the furrow system and an analysis of circularity of impact craters is addressed. The hypothesis that the furrow system was initially concentric and that the present configuration of the furrows provides a measure of lateral motion of dark terrain is tested by determining the present centers of the furrow system in several dark terrain blocks and observing the amount of deformation in bright terrain regions which separate these blocks. An upper scale limit is placed on the amount of extension associated with bright terrain formation by using the deviation from circularity of impact craters to calculate the strain field around wedge-shaped regions of bright terrain. Penetrative deformation in Ganymede's lithosphere is identified by examining the circularity of impact craters in dark terrain.

Zuber, M. T.↗

NASA NTRS1984

Venus - The nature of the surface from Venera panoramas

The present investigation has the objective to analyze the information collected by the Soviet Venera 9, 10, 13, and 14 lander spacecraft imaging systems. The analysis is to make a systematic comparison with other planetary surfaces possible, and an improved understanding of the surface of the planet Venus is to be provided. Attention is given to the imaging systems and transformation methods, observations, the observed characteristics of Venera lander sites, and an interpretation of the geological processes responsible for the features observed in the Venera panoramas. It is concluded that the present Venus environment is considerably different in terms of temperature, pressure, and atmosphere composition from the present terrestrial subaerial environment.

Garvin, J. B.↗

NASA NTRS1984

Venus: The nature of the surface from Venera panoramas

Images of the surface of Venus obtained by the Soviet Venera 9, 10, 13 and 14 landers are analyzed to provide a basis for understanding the nature of geologic processes operating there. Bedrock is exposed at the Venera 10, 13 and 14 sites and is characterized by semi-continuous, flat polygonal to subrounded patches up to several meters in width. The bedrock surface is often dominated by sub horizontal to horizontal layered plates with thicknesses of several cm and abundant linear and polygonal vertical fractures. Soils (particles 1 cm) are abundant at the Venera 9, 10 and 13 sites, but are uncommon at Venera 14. Features indicative of a strong aeolian influence (moats, dunes, wind tails) are not observed. Several hypotheses are considered for the origin of the bedrock surfaces, and it is concluded that bedrock originated from surface lava flows. The relative freshness of features observed by the Veneras suggests that erosion rates are very low or that some bedrock surfaces are geologically young.

Garvin, J. B.↗

NASA NTRS1984

Lithospheric stresses due to radiogenic heating of an ice-silicate planetary body - Implications for Ganymede's tectonic evolution

Thermal evolution models of differentiated and undifferentiated ice-silicate bodies containing long-lived radiogenic heat sources are examined. Lithospheric sresses arise due to volume change of the interior and temperature change in the lithosphere. For an undifferentiated body, the surface stress peaks early in the evolution, while in the differentiated case, stresses peak later and continue to accumulate for longer periods of time. The variation of near-surface stress with depth shows that stresses for the undifferentiated body initially penetrate to great depths, but rapidly concentrate within a few kilometers of the surface. For the differentiated body, elastic stresses never accumulate at a depth greater than a few kilometers. These models are applied to consider long-term rdioactive heating as a possible mechanism of tectonic activity and bright terrain formation on Ganymede.

Zuber, M. T.↗