Solar System Exploration: Space Science Highlight

1. Solar System Exploration: Space Science Highlight Polygonal Plains on Venus Linked to Global Climate Change Featuring the Research of Suzanne E. Smrekar, Pierre Moreels, and Brenda J. Franklin To be published in the Journal of Geophysical Research: JGR Planets Characterization and Formation of Polygonal Fractures on Venus Contact: Suzanne.E.Smrekar@jpl.nasa.gov

2. Solar System Exploration: Space Science Highlight Planetary Scientists are exploring Venus today By examining radar image mapping sent back by NASA’s Magellan Mission nearly a decade ago… What can we learn about Earth by exploring Venus? Greenhouse effects of global warming occur on both planets. Interplay between the atmosphere and lithosphere can stabilize--or destabilize-- global climate change over multimillion year time scales… Space Science Highlight prepared by Richard Shope

3. Solar System Exploration: Space Science Highlight Solving the Mystery of the Polygons of Venus What play of forces best explains the magnitude and uniformity of polygon size at over 200 sites? Polygons average ~2 km across. Global Climate Change Model Fits Best! Are polygons stratigraphic markers?

4. Solar System Exploration: Space Science Highlight • Venus Polygons… • Diameter measured • In thousands of meters • Typically ~2 kilometers Did Giants form these polygons on Earth…? Giant’s Causeway…Ireland Polygons formed from cooling of volcanic lava flow Diameter measured in meters http://www.giantscausewayofficialguide.com Space Science Highlight prepared by Richard Shope

5. Solar System Exploration: Space Science Highlight Venusian Polygons…What titanic forces caused them to form? Volcanism? Subsurface Heating? Global Climate Change? Evidence: Uniform size ~ 2km across Global distribution ~ 200 sites Fits Global Climate Change Model Space Science Highlight prepared by Richard Shope

6. Solar System Exploration: Space Science Highlight Venusian polygons have average diameter of 1.8 ± 0.9 km Example of gradation in size from large to small. Polygons in this region range from 6 km near top to 1 km near bottom. (Fmap 35S253, Figure 1 in Smrekar et. al. JGR-Planets, to be published.) Several orders of magnitude larger than on Earth 82 km

7. Solar System Exploration: Space Science Highlight SIGNIFICANT RESULTS Polygonal fractures on Venus indicate Global Climate Change process Global Distribution of Polygons on Venus Model validated by new study: Anderson and Smrekar (1999) proposed Global Climate Change Model as mechanism of formation of polygonal terrain: global warming following by gradual cooling produces sufficient thermal stresses to produce strains on surface and observed fracture spacing.

8. Solar System Exploration: Space Science Highlight 100 Million Years 100 Million Years 100 Million Years Temperature 900˚K Volatiles release, clouds form Surface Climate stabilizes H escapes H2O 800˚K SO2 Clouds reduce 700˚K Gradual Cooling Results in Additional Extensions Reheating Causes Expansion Tectonic Effects of Global Climate Change on Venus Time0 ~ 750 Million years ago Rapid Cooling Causes Contraction To depth: of ~20 km

9. Solar System Exploration: Space Science Highlight TALKING POINTS FOLLOW FROM THIS POINT

10. Solar System Exploration: Space Science Highlight Venus Polygons How did they form? THREE Proposed formation mechanisms • Volcanism: Cooling following lava flow emplacement • Why? • Polygons typically found on surface of slowly cooled lava flows • Why NOT? • To obtain large size, would need to be a lava flow 20 km thick • Lithospheric heating • Why? • Local heating events consistent with lithospheric cooling • Why NOT? • Inconsistent with variable size and pattern of diminishing size moving away from center of heating • Global Climate Change… Space Science Highlight prepared by Richard Shope

11. Solar System Exploration: Space Science Highlight SIGNIFICANT RESULTS Features Best Explained by Atmospheric and Surface Interaction Observations tend to validate global climate change model Anderson and Smrekar (1999) propose Global Climate Change Model as mechanism of formation of polygonal terrain: global warming following by gradual cooling produces sufficient thermal stresses to produce strains on surface andthe observed fracturespacing.Builds on work of Bullock and Grinspoon (1996, 2001): Resurfacing event ~750 M years ago triggers volatile outgassing of H2O and SO2, which form clouds leading to a temperature rise of 90º-200º. Exospheric escape of H2O and reaction w/surface minerals causes reduction in cloud cover leading to cooling. Over time atmospheric albdeo and opacity return to normal and temperature equilibrates. The whole cycle lasts 300 million years. Space Science Highlight prepared by Richard Shope

12. Solar System Exploration: Space Science Highlight Polygon Plains are found at 204 sites all over Venus • Nathan Bridges has mapped Venusian geologic regions • About 50% of polygons are near shield volcanoes • About 50% of polygons are in regions of varied terrain Space Science Highlight prepared by Richard Shope

13. Solar System Exploration: Space Science Highlight Future Mapping May Reveal Polygons as Stratigraphic Markers Venus appears to have experienced a period of high resurfacing rate consistent with volcanic outgassing capable of producing global climate change--if all polygons formed in same period, mapping efforts could explore whether polygons are stratigraphic markers. Section of Fmap 77N355, with a size of 66 x 53 km. Locations “a” show polygons crossing an apparent flow boundary. At “b” a younger volcano covers preexisting polygons. Space Science Highlight prepared by Richard Shope

14. Solar System Exploration: Space Science Highlight Lower Right Related Papers Anderson, F.S. and S.E. Smrekar, Tectonic effects of climate change on Venus, J. Geophys. Res, 104, 30, 743-30, 756, 1999. Bullock, M. A., and D.H. Grinspoon, The stability of climate on Venus, J. Geophys. Res., 101, 7521-7529, 1996. Bullock, M. A., and D.H. Grinspoon, The recent evolution of climate on Venus, Icarus, 150, 19-37, 2001. Space Science Highlight prepared by Richard Shope