Mercury and Venus

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Mercury and Venus

• Paul J. Thomas
• Department of Physics and Astronomy
• University of Wisconsin - Eau Claire

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Mercury

• Diameter 4880 km
• 32 spinlocked
• 88 day orbital period
• 59 day rotation period
• Missions
• Mariner 10 (1974)
• Messenger (2011)

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Types of Faults
Thrust Fault
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Horst and Graben
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Mercury
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Caloris Basin
1350 km in diameter
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Caloris Basin from Messenger, 2008
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Mercurys Iron Core

• Mercury
• Core radius 75 of planetary radius
• Density 5430 kg/m3
• Earth
• Core radius 55 of planetary radius
• Density 5520 kg/m3

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Venus
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Venus

• Thick CO2 atmosphere (90 bars at surface)
• Sulfuric acid droplets form opaque clouds (detail
  visible in UV)
• Radar can penetrate to surface - Magellan radar
  mapper (1989-92)
• Surface at several locations has basalt
  composition

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Venus
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Plate Tectonics
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The Surface of Venus
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Magellan Radar Images
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Volcanism
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Coronae
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Venus

• US Pioneer Venus Mission (1979)
• H2O in Venus atmosphere 10-5 ? Earths
• HDOH2O ratio 150 ? Earth, chondrite
• Conclusion
• Venus has lost enormous amounts of H2O in its
  history.

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Vibrational Modes of CO2
Asymmetric Stretch
Vertical Bend
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Venus

• Runaway Greenhouse effect may have produced
  massive loss of water in Venuss past
• On Earth, excess CO2 was scrubbed out of
  atmosphere by rain and deposited in carbonate
  rocks

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Runaway Greenhouse Effect
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Venus

• Wide range of tectonic, volcanic and impact
  features in Magellan radar maps
• Volcanic activity probably continues
• Perhaps massive global melting every 500 Myr
• Plate tectonics almost certainly absent