Metrics for in-space telescope assembly techniques
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space telescopes↗
Engineering topics
Stephens, S. K.
Publications and source records attributed to Stephens, S. K..
Carbonate formation on Mars: Latest experiments
Laboratory simulations of Martian CO2 storage address whether carbonate formation could have reduced CO2 pressure from a hypothetical greater than 1 bar to the present 7 mbar in less than or equal to 3 to 4 billion years. This problem is addressed with experiments and analysis designed to verify and improve previous kinetic measurements, reaction mechanisms, and product characterizations, with the goal of improving existing models of Martian CO2 history. A sensitive manometer monitored the pressure drop of CO2 due to uptake by powdered silicate for periods of 3 to 100+ days. Pressure drops for diopside 1 and basalt show rapid short-term (approximately one day) CO2 uptake and considerably slower long-term pressure drops. Curves for diopside 2, olivine 1, and olivine 2 are qualitatively similar to those for diopside 1, whereas quartz and plagioclase show near-zero short-term pressure drops and very slow long-term signals, indistinguishable from a leak (less than 10(exp 11) mol/sq m/s).
Stephens, S. K.↗
Ground-based near-infrared imaging observations of Venus during the Galileo encounter
Near-infrared images of Venus, obtained from a global network of ground-based observatories during January and February 1990, document the morphology and motions of the night-side near-infrared markings before, during, and after the Galileo Venus encounter. A dark cloud extended halfway around the planet at low latitudes and persisted throughout the observing program. It had a rotation period of 5.5 + or - 0.15 days. The remainder of this latitude band was characterized by small-scale (400 to 1000 km) dark and bright markings with rotation periods of 7.4 + or - 1 days. The different rotation periods for the large dark cloud and the smaller markings suggest that they are produced at different altitudes. Midlatitudes (+ or - 40 to 60 deg) were usually occupied by bright east-west bands. The highest observable latitudes (+ or - 60 deg to 70 deg) were always dark and featureless, indicating greater cloud opacity. Maps of the water vapor distribution show no evidence for large horizontal gradients in the lower atmosphere of Venus.
Crisp, D.↗
On Venus impact basins - Viscous relaxation of topographic relief
The viscous relaxation with time of the topographic relief of impact basins on Venus is calculated under the assumption that the surface temperature of the planet has been at or near its presently high value since the time of basin formation. The effects of a decrease in effective viscosity with depth and of the partial to complete isostatic compensation of initial topography are included in the model. An impact basin several hundred kilometers or greater in diameter and three billion years old or older should have negligible topographic relief at present. On this basis, the hypothesis that quasi-circular features of low radar backscatter but little topographic relief may be relaxed remnants of ancient impact basins cannot be excluded. However, large quasi-circular depressions on Venus, such as Atlanta Planitia, are unlikely to be remnants of impact basins, because of their current relief, and so some other process should be found to account for them.
Solomon, S. C.↗