Phases of Venus

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Phases of Venus
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Share Question

• How much more solar energy does Venus receive
  than the Earth, due to the fact that Venus is
  0.72 times as far from the Sun?
• a) 0.72 times as much
• b) 1/0.72 1.4 times as much
• c) 0.72 (squared) 0.52 times as much
• d) (1/0.72) (squared) 1.92 times as much

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Views of Venus
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Transit of Sun by Venus
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Rotation Axis of Venus
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A Day at Venus
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(Abridged) Exploration of Venus

• 12/62 Mariner 2 (US)
• 10/67 Venera 2 (Sov) 1st surface contact
• 10/75 Venera 9 and 20 (Sov) 1st surface
  photos
• 1990-92 Magellan (US) global radar mapping

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Venera Lander
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Magellan Radar Mapping of Venus
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Atmosphere of Venus

• Discovered by Lomonosov (Rus.) in 1761
• Venus is almost equally hot everywhere, implying
  efficient circulation
• Pole-equator Hadley cell
• 360 kph westward flow at cloud level at equator
  (wind circuits planet in 4 days)
• Surprisingly fast wind for a slowly rotating
  planet!

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IR Spectra of the Terrestrials
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Earth/Venus Atmospheres
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Atmospheric Characteristics
Surface pressure P 90 atms
Surface density r 50 rE 0.05 rH2O
Surface temperature T 720K
Atm. composition CO2
Atm. scale height H 16 km
Cloud layer 44 km
Cloud composition Sulfuric acid
Reflected sunlight 80
Sunlight at surface 2.5
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Temperature Profile of Venus
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Greenhouse Effect (Carl Sagan, 1962)

• Selective Absorption
• CO2 absorbs IR better than visible light
• Sun emits mostly at 0.5 microns, but planet
  surfaces glow mostly around 3-30 microns
• Suggests there is more energy getting in than out!

• Radiative Equilibrium (RE)
• RE demands that energy in and out must balance!
• The trapped (blanketed) energy heats up surface,
  which becomes brighter.
• Continues until the fraction escaping from below
  equals the total getting in from above.

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The Greenhouse Effect
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Surface Properties

• Mostly rolling volcanic plains of basaltic rock
• No active volcanoes observed, but
• Young surface
• Many volcanoes, mostly of shield type
• Fluctuating SO2 levels
• Few impact craters
• Volcanic resurfacing has been important!

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Venusian Terrain
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Volcanos at Venus
Results from Venus Express
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Venus May Have Active Volcanism

• Venus has few impact craters, suggesting the
  entire surface is younger than 1/2 billion years
• Venus has clouds of SO2 (a volcanic gas) and many
  volcanoes - but active volcanism has not been
  detected
• New infrared observations indicate some regions
  were resurfaced in the last 100s to 10,000s of
  years. Venus was recently (and still may be)
  volcanically active.

Radar and topography image from the Magellan
spacecraft of Idunn Mons on Venus, which was
recently volcanically active. Dark regions are
smooth, and bright regions are rough or steep.
Elevations have been exaggerated thirty times.
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Interpreting Surface Hot Spots

• Thermal emissivity indicates how efficiently a
  material radiates heat
• Some volcanic regions of the Venus surface have
  higher emissivity than their surroundings
• Lower emissivity regions have reacted chemically
  with CO2 and SO2 in the atmosphere, forming a
  thin crust over the lava
• High emissivity indicates younger material that
  has not been substantially weathered by Venus
  thick atmosphere

Infrared observations from the Venus Express
spacecraft overlaid on the image from the Slide 1
show that Idunn Mons (red) has higher thermal
emissivity than its surroundings (blue). This
indicates a compositional difference between the
two regions.
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The Big Picture

• Scientists debate whether the entire planet was
  resurfaced in a large global event, or gradually
  over time
• The new observations of localized recent
  volcanism suggest that the global hypothesis can
  not be the entire story. Some scientists believe
  the results strongly support the gradual
  hypothesis
• The three regions in this study are all
  geologically similar to Hawaii, where hot
  material from deep inside the planet causes
  uplift and volcanism at the surface.

Global radar image of Venus from Magellan. The
approximate location of Idunn Mons, from previous
slides, is indicated.
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Venusian Relief Map
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Venusian Interior

• Similar to Earths
• However, no magnetic field
• Venus slow rotation implies little circulation
  in core
• NO DYNAMO ACTIVITY
• No evidence for plate tectonics, large crustal
  motions, or mountain ranges