The Geomorphology and Landforms of Venus

Introduction Atmosphere and Climate Surface Geology and Landforms Conclusions

Size (radius)3,760 miles3, 960 miles Age~ 4.5 billion years Distance from Sun67 million miles93 million miles Surface Temp470 C14 C Surface Pressure90 atm1 atm % atmo. CO296%0.04% Basilevsky and Head, 2003

Introduction Atmosphere and Climate Surface Geology and Landforms Conclusions

High carbon dioxide content causes higher pressure Not a significant variation in T & P across diurnal cycles Temperature decreases with altitude Four separate inversions (temperature increases with altitude) No internal magnetic field Very susceptible to solar winds Hydrogen has been stripped away Atmosphere and Climate

Greenhouse Effect -Volcanic outgassing is a major source of sulfur dioxide and carbon dioxide to the atmosphere -Carbon monoxide and hydrochloric acid also present Volcanic outgassing resulted in sulfuric acid cloud formation -Cooled the surface by blocking sunlight -Dissipated, temperatures increased

Introduction Atmosphere and Climate Surface Geology and Landforms Conclusions

Topography Plains and low-lying areas (80% land area) Basaltic lithospheric plates More resistant to breakage, plates are not as numerous or as global as Earth’s plates Ridges, mountain belts, and plateaus are present, but minimal Weak, convection-driven tectonics Deep-subduction does not occur from Basilevsky and Head, 2003

Geologic History million years agoAge of post-regional plain lava flows and volcanic constructs 300 millionYoungest possible mean age of surface million Age of lobate plains -Relatively young feature, few craters millionMean surface age determined by mean crater density 800 million-1 billionAge of tessera terrain 1 billionOldest possible mean age of surface 4.5 billionAge of Venus from Basilevsky and Head, 2003

Volcanoes Satellite images reveal flows, vents, and shield volcanoes from 100-m to 100-km (horizontal) scale Volcanic plains overlie mantle plumes Increased deformation in these areas Major contributor to global resurfacing event Overprinting of tectonic deformation and impact craters that originated before event Basilevsky and Head, 2003

Impact Craters Important age-determining feature Crater density increases with time (# craters / unit area) Mostly large craters (> 35 kilometers in diameter) due to Venus’s atmosphere Erosion rates are low in cratered regions, so deformation is assumed to be volcanic or tectonic in origin Spatial differences in erosion rates

Valley Networks Associated with more deformed regions of Venus Valley networks are structurally controlled Low-viscosity lava caused valley networks to propagate Lava enters pre-existing fractures and expands Komatsu et al. (2001) classified 3 types: Rectangular

LabyrinthicIrregular

Valley Networks (cont.) Hecate chasma: series of troughs and fractures

Coronae and novae Corona: surface feature caused by mantle plumes, often occur within or near valley networks -Form as intrusions and are centered on an annulus of fractures and ridges Nova: radial network of grabens

Coronae and novae Aittola and Raitala (2005): Half of novae reside within coronae Coronae with novae tend to be younger than singular coronae. - Useful in determining the relative age of certain regions of Venus.

Introduction Atmosphere and Climate Surface Geology and Landforms Conclusions

A near-global resurfacing event occurred on Venus between 500 million and 1 billion years ago Volcanic and tectonic activity subsequently decreased, allowed impact craters and valley networks to accumulate Atmospheric conditions alter, and are altered by, the surface geologic activity Interpreting the processes that occur on Venus are key to understanding more about the geologic history of Earth and other planets in our Solar System Venus can be seen as a model for Archean plate tectonics on Earth (Anderson, 1981)

References: Aittola, M. and J. Raitala, 2005: Coronae and Novae in the Hecate Chasma Deformation Area. Solar System Research, vol. 39, pp Basilevsky, A. T. and J. W. Head, 2003: The surface of Venus. Reports on Progress in Physics, vol. 66, pp Komatsu, G., V. C. Gulick and V. R. Baker, 1999: Valley networks on Venus. Geomorphology, vol. 37, pp Howard, H. T., G. L. Tyler, G. Fjeldbo, A. J. Kliore, G. S. Levy, D. L. Brunn, R. Dickinson, R. E. Edelson, W. L. Martin, R. B. Postal, B. Seidel, T. T. Sesplaukis, D. L. Shirley, C. T. Stelzried, D. N. Sweetnam, A. I. Zygielbaum, P. B. Esposito, J. D. Anderson, I.I. Shapiro, and R. D. Reasenberg, 1974: Venus: Mass, Gravity Field, Atmosphere, and Ionosphere as Measured by the Mariner 10 Dual-Frequency Radio System. Science, vol. 183, pp Masursky, H., E. Eliason, P. G. Ford, G. E. McGill, G. H. Pettengill, G. S. Schaber and G. Schubert, 1980: Pioneer Venus Radar results: Geology from images and altimetry. Journal of Geophysical Research, vol. 85, pp Pollack, J. B., O. B. Toon, and R. Boese, 1980: Greenhouse models of Venus’ High surface temperature, as constrained by Pioneer Venus measurements. Journal of Geophysical Research, vol. 85, pp Images: Universetoday.com and above references