Lecture 8

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Lecture 8 Surface and Atmosphere of the Inner
Planets
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Terrestrial Planets
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Basic Information
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Atmosphere of the Earth

• Composition
• Nitrogen (78)
• Oxygen (21)
• Trace molecules -- Argon, Carbon Dioxide (CO2),
  Water vapor (H2O), and others
• Protects us from
• harmful radiation
• meteoroids falling from space
• Keeps surface of planet warm
• Greenhouse effect

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Atmosphere of Mercury

• No true atmosphere
• Some particles from solar wind eddy around
  Mercury and then leave
• Temperature too high
• Cannot hold gases
• Extreme temperature variations
• 100 (night) to 700 K (day)
• No insulating atmosphere
• One solar day on Mercury 176 Earth days!

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Atmosphere of Venus

• Permanent cloud cover keeps surface hidden.
• Composition
• Mostly CO2
• little water.
• Clouds contain droplets of sulfuric acid
• Temp 750 K
• Pressure almost 90 atm

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Greenhouse Effect

• Sunlight hits surface of planet warming the
  ground.
• Planet radiates heat in the form of infrared
  radiation

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Greenhouse Effect

• Greenhouse gases (CO2, H2O) traps infrared
  radiation, keeping the planet warm.
• Planet eventually comes to equilibrium and
  temperature stops increasing

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Atmosphere of Mars

• Composition
• mainly CO2
• Very thin.
• Temperature
• 100 K to 300 K
• Strong winds cause dust storms
• Thin clouds, fog

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Sand Dunes -- Mars Surveyor
Image area 2.3 x 3.6 km
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Origin of Earths Atmosphere

• Original atmosphere was H and He leftover from
  formation of SS.
• Too hot near the Sun
• H and He are very light elements.
• Gravity of Earth could not hold them.

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• Second atmosphere was possibly out-gassed from
  volcanoes.
• water vapor, methane, carbon dioxide (CO2),
  nitrogen (N) compounds.
• N freed by UV light
• Earth cooled, water vapor condensed into oceans.

• CO2 dissolved in oceans or became locked up in
  rocks.

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• Current atmosphere is mainly N and O
• 3.8 3.5 billion years ago life evolved,
  releasing O into atmosphere via photosynthesis.
• Free oxygen does not build up until 2 billion
  years ago
• Ozone layer formed after free oxygen increases.

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Continuing Questions

• Was atmosphere created gradually or were most
  gases released early when surface was still
  molten?
• Could comet impacts have added some carbon
  dioxide and water? How much?

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Why are Venus and Mars Different from the Earth?

• Venus -- too close to Sun
• Too hot for water to condense.
• CO2 was not trapped in the oceans.
• Increased the greenhouse effect
• Runaway Greenhouse Effect
• Mars -- too far from the Sun
• Initially warm after formation, water condensed.
• Water trapped CO2
• Water Froze, trapping CO2
• Less greenhouse effect

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Tidal Forces

• Gravity of Moon pulls on Earth
• Force on near side stronger than far side

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Tidal Forces

• Net result is to pull object apart.
• Difference in forces on far and near side tidal
  force
• Causes bulge in water on Earth.
• Earth also slightly distorted

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Surface of Mercury

• Appears similar to Moon
• Temp 100 K (night) to 700 K (day)
• Heavily cratered due to bombardment by debris in
  space.
• No weather or geologic activity
• Any crater that is formed remains.

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Craters on Mercury
Mercury
Moon
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Surface Features

• Heavily cratered areas (similar to lunar
  highlands)
• Surface likely 3.8 byrs or older
• Inter-crater plains (similar to lunar maria)
• Likely formed in same manner as on Moon.
• More craters than on lunar maria likely formed
  early than maria.

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Inter-crater Plains
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Scarps

• Cliffs in crust of planet which cut across
  craters.
• Formed when interior cooled and core shrunk more
  than the crust.
• Crust developed wrinkles.

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Caloris Basin

• Enormous crater - possibly due to large impact

Mare Orientale (Moon)
Caloris Basin
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Weird Terrain
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Synchronous Orbit of Mercury

• Pspin59 days
• Porb88 days
• Mercurys orbit is eccentric (0.21)
• Mercury is slightly elongated
• Tidal forces of Sun try to align Mercury

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Surface of Venus

• Mapped by Magellan (radar) probe
• Some craters
• Many volcanoes
• No water

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Venus - Magellan

• Radar maps of Venus
• (Left image bright rougher terrain)
• (Right image colored to resemble Earth globe)

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Venus Magellan
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Craters

• Impacts occur
• Fewer craters
• thicker atmosphere
• geologic activity

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Venera

• Venera probes (Russian) landed on Venus.
• Hot and dry

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Surface of Mars

• Red colored -- iron oxide (rust) in surface
  rocks.
• Canali
• Dark lines observed by Sciaparelli (1877)
• Believed to be irrigation channels.
• Natural surface features.
• No liquid water (too cold)

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Surface -- Pathfinder Mission
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Pathfinder
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Twin Peaks -- Pathfinder
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Water on Mars

• Dry riverbeds seen
• Channels are 4 billion years old.
• Mars was warmer earlier in its history.
• Thicker atmosphere.
• Cooled slowly

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Where is the Water Now?

• Polar caps.
• water polar caps -- permanent
• CO2 caps grow during winter and shrink during
  summer.
• Frozen under surface as permafrost.
• Occasional melting
• Volcanic activity
• Meteor impacts

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Polar Caps
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Martian Gullies
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Moons of Mars

• Phobos and Deimos
• Irregular shape
• Heavily cratered
• Rotate synchronously (like Earths Moon)

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Deimos
Size 15 x 12 x 11 km
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Phobos
Size 27 x 22 x 19 km
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Life on Mars

• Martian meteorite
• Found at South Pole
• May have been blasted off of Mars by an impact.
• Much debate over validity of results.
• Possible contamination by Earth life.
• Need sample from Mars.
• Viking -- tested soil samples, no clear evidence
  for current life.
• Mars Pathfinder -- no clear evidence for current
  life.