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Part II: Building a Goldilocks World

From the Big Bang to Habitable Planets. Part II: Building a Goldilocks World. Outline: Formation of the planets Distribution (and redistribution) of volatiles Heat production and transport Radiation budget The traditional habitable zone.

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Part II: Building a Goldilocks World

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  1. From the Big Bang to Habitable Planets Part II: Building a Goldilocks World

  2. Outline: Formation of the planets Distribution (and redistribution) of volatiles Heat production and transport Radiation budget The traditional habitable zone Based on the approach in Jim Kasting’s “How to Find a Habitable Planet”

  3. Planet Formation

  4. Modeling Accretion Chambers, 2001

  5. Condensation of Volatiles in the Circumstellar Disk

  6. Condensation of Volatiles in the Circumstellar Disk Earth Jupiter Saturn Uranus 2000 Metals Temperature (K) Silicates 1000 Water Ice Ammonia Ice 0 15 20 5 10 Distance from Sun (AU)

  7. This model does a good job of explaining the distribution of rocky, gas giant, and ice giant planets But not so much the presence of Earth’s oceans . . .

  8. Volatiles are redistributed from the outer to the inner solar system by asteroids and comets (which, recall, carry more than just volatiles . . . )

  9. Heat

  10. Accretion and Impacts Deliver Energy (much of which becomes heat)

  11. So does radioactive decay . . . 238U → 234Th + α (this is nuclear fission (= energy – remember?))

  12. Consequences of Interior Heating I. Differentiation

  13. II. Liquid Core = Earth’s Dynamo (Magnetic Field)

  14. Volcanism and Plate Tectonics • (important for many reasons – we’ll discuss one now, one later)

  15. A chemically and thermally differentiated planet is like a battery . . . = Volcanic activity connects the terminals

  16. Chemical Energy for Life

  17. Bigger bodies (= higher SA/Vol) cool more slowly, and may have more active or longer lasting volcanism as a result

  18. Is this geological heating what keeps the surface of our planet warm (and our water in liquid form)? Nope. Only about 0.025% of surface heating comes from geothermal heat flux. The rest comes from…

  19. Solar Radiation Budget

  20. Radiation Budget (mostly infrared) Absorbed (Visible) Energy = Radiated (Infrared) Energy (mostly visible) d Radiation intercepted by planet goes as 1/d2 (NASA Earth Observatory)

  21. Got Liquid Surface Water? (simple view) Too Hot Just Right Too Cold

  22. Negative Feedback on Greenhouse Warming The Carbonate Silicate Cycle Constant source while volcanism is active Ocean-atmosphere exchange required to make this happen Puts CO2 back into circulation Enhanced by biology. Would still happen without, but with higher CO2 levels Enhanced by higher temperature, more CO2 (courtesy Jim Kasting)

  23. Cautionary Tales for Worlds Aspiring to Habitability

  24. Venus and the Runaway Greenhouse

  25. Mars: The Case of the Missing Greenhouse Effect

  26. The Traditional (Liquid Water) Habitable Zone http://www.dlr.de/en/desktopdefault.aspx/tabid-5170/8702_read-15322/8702_page-2/

  27. Extras

  28. Hiroshima Terrestrial Impact Frequency year Tunguska century Tsunami danger ten thousand yr. Global catastrophe “Armageddon” Impact (Texas-sized!) million yr. K/T billion yr. 0.01 1 100 10,000 million 100 million TNT equivalent yield (MT) (Credit: D. Morrison) “Catastrophic” depends on who you are and where you live . . . “Catastrophic” depends on who you are and where you live . . .

  29. 0 Heat-Sterilized Impact Heating Depth (km) 1 Geothermal Gradient 2 0 100 200 Temperature (°C) Surface-Sterilizing Impacts Habitable (Sleep & Zahnle, 1998)

  30. Effects of Impacts on Established Life: Interplanetary Transfer of Life?

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