Venus
What’s the deal with Venus?
-Its lithosphere thickens over time—compare with Earth’s lithosphere
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becomes unstable (negatively buoyant; sinks in fluid)
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(irrelevant website but worth a look because it’s weird http://www.drownproofing.com/)
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volcanism occurs every ~500 m.y. (will it happen in our lifetime?!)
o if Venus started to erupt, it would emit  CO2, SO2 (mostly), CO, H2O
(gases)
o more SO2 in atmosphere than there should be without some method of
input
 the compound decays rapidly
Volcanism on Venus? (Jess’ 15 minutes)
Active volcanism on Venus in the Ganiki Chasma rift zone (Shalygin et
al.)
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Earth and Venus  similar in size, composition, closeness to Sun, density
Over 1600 major volcanoes  but are any of them active?
o Ganiki Chasma rift zone
 4 areas of interest found in the rift zone that may link to active
volcanism on the Venus
(http://www.hou.usra.edu/meetings/lpsc2014/pdf/2556.pdf)
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Variation in emissivity cannot exceed that of ideal black body
o Stefan-Boltzmann law  M = σT^4
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Variations in brightness due to differences in emissivity
(Shalygin; Figure 2)
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similar to eruptive activity on Earth
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hotspots on Venus likely to have effusive eruptions
Conclusion: Yes, there is most likely active volcanism on Venus!
Venus analogous to Mars…pressure of hotspot
Negative diapir (sagduction) – controlled by viscosity
Low viscosity zone (Water-rich asthenosphere)
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without asthenosphere, tectonic motion not possible
delamination—lower parts of lithosphere are recycled (is this the only way
lithosphere evolves on Venus?)  Himalayan Mountains on…Earth…may be
analogous to what is occurring on Venus
Question: “How long does it take for basalt to cover an Earth-sized planet (aka Venus)?”
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look at the craters
no remnant of ancient basins; thickness of flows must have eradicated any
evidence of them
Earth’s stratigraphic column vs. Venus’ stratigraphic column
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single datum for Venus (average surface crater age)
o Tessera Terrain may yield more knowledge (?)
 chemistry of the atmosphere records history of volcanism
D/H (deuterium/hydrogen) ratio goes up with loss  150X terrestrial
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Ocean may have persisted for ~1 Ga (?)
Life evolved on Earth; why not on Venus (or Mars)
Venus does not have magnetic field today
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Why?
o No active dynamo; Ra equation (no ΔT)
o Stagnant lid…how does heat get out?  conduction, which is lamer and
weaker than Earth’s convection
 Overturn to magnetic field (?)
o Though mantle is not completely dry, does not have volatile lubrication
(i.e. water on Earth allowing for plate tectonism)
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Plate tectonics on Earth!
o Breaking of lithosphere allows for convection, which is way more efficient
than conduction (ex. volcanoes, subduction zones, MORs)
Core-accretion theory of planet formation…put to the test (Gloria’s 15 minutes)
Water vapour absorption in the clear atmosphere of a Neptune-sized
exoplanet (Fraine et al. 2014)
WHY?
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Previous attempts to measure molecular absorption were unsuccessful
How were data gathered?
o Hubble, Spitzer, Kepler
(Figure 1a)
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Difference in temperature dependent on wavelength
What’re those?
(Figure 1b)
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farther left; hotter
starspots are too hot to mimic absorption
What is amplitude of starspot absorption?
Hubble data (Figure 2)
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Atmospheric scale height is inversely proportional to avg. molecular weight
Conclusion
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Starspots are too hot to mimic observed absorption
Atmosphere had metallicity ~700 solar
Mean molecular weight ~10.2g mol^-1
Exoplanet HAT-P-11b is smallest and coldest planet