(1) Goodbye to Mars, (2) Why planets have atmospheres.
Transcript of (1) Goodbye to Mars, (2) Why planets have atmospheres.
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(1) Goodbye to Mars, (2) Why planets have atmospheres
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What have we learned from the MERs and “Mars Phoenix”
• It now seems clear that there were standing bodies of water for long periods of time early in Martian history
• Evidence is presence of hematite, jarosite, and other minerals that form in lakes or oceans
• Relative absence of carbonate rocks is due to alternative chemistry in acidic water
• But, apparently oldest rock strata do contain carbonate rocks and clay (montmorillonite)
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The launch, interplanetary journey, and arrival at Mars of an MER spacecraft
The journey to Mars of "Spirit"
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In the future…Mars Science Laboratory
Launch in fall, 2011, arrival fall 2012. Will make tests for organic chemicals, biological molecules
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The El Dorado of future missions:
Mars Sample Return
romEarth) in 2014.
Stay tuned!
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Atmospheres: some planets have them, some don’t
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Whether a planet has an atmosphere or not depends on the relative magnitude of
two speeds
• The speed at which molecules move around in the gas (thermal speed)
• The speed of escape from the planet (escape speed, depends on mass and radius of a planet)
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The distribution of molecular speeds depends on the temperature
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The criterion for hanging onto an atmosphere
• Depends on relative magnitude of escape speed and average molecular speed
• If molecular speed > about 1/6 of escape speed, atmosphere will “leak out” over a period of billions of years
• If molecular speed << 1/6 of escape speed, the planet should retain the atmosphere.
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Above rule of thumb seems to roughly work (see Table 7.3), but there are some
mysteries. Example: Mars and Titan
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Where we have been so far…the inner solar system and the terrestrial planets
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Now let’s move out further in space…the outer solar system and the Jovian planets
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Jupiter and Saturn are giants
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Our first look at Jupiter and Saturn
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Exploration of Jupiter
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The atmospheric structure of Jupiter
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The cloud bands of Jupiter
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The Galileo Probe
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The interior structure of Jupiter (and Saturn)