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

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 Kastings How to Find a Habitable Planet

Planet Formation

Chambers, 2001 Modeling Accretion

Condensation of Volatiles in the Circumstellar Disk

Jupiter Uranus Distance from Sun (AU) Saturn Temperature (K) Earth Silicates Metals Water Ice Ammonia Ice Condensation of Volatiles in the Circumstellar Disk

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

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

Heat

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

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

Consequences of Interior Heating I. Differentiation

II. Liquid Core = Earths Dynamo (Magnetic Field)

III.Volcanism and Plate Tectonics (important for many reasons – well discuss one now, one later)

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

Chemical Energy for Life

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

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

Solar Radiation Budget

(mostly visible) (mostly infrared) (NASA Earth Observatory) Radiation intercepted by planet goes as 1/d 2 d Radiation Budget Absorbed (Visible) Energy = Radiated (Infrared) Energy

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

Negative Feedback on Greenhouse Warming The Carbonate Silicate Cycle (courtesy Jim Kasting) Constant source while volcanism is active Enhanced by higher temperature, more CO 2 Puts CO 2 back into circulation Enhanced by biology. Would still happen without, but with higher CO 2 levels Ocean-atmosphere exchange required to make this happen

Cautionary Tales for Worlds Aspiring to Habitability

Venus and the Runaway Greenhouse

Mars: The Case of the Missing Greenhouse Effect

The Traditional (Liquid Water) Habitable Zone

Extras

year century million yr. billion yr. ten thousand yr. 100 millionmillion10, Hiroshima Tunguska K/T TNT equivalent yield (MT) Global catastrophe Tsunami danger (Credit: D. Morrison) Terrestrial Impact Frequency Armageddon Impact (Texas-sized!) Catastrophic depends on who you are and where you live...

Temperature (°C) Depth (km) Geothermal Gradient Surface-Sterilizing Impacts (Sleep & Zahnle, 1998) Habitable Heat-Sterilized Impact Heating

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