From the Big Bang to Habitable Planets Part

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 Based on the approach in Jim Kasting’s “How to Find a Habitable Planet” The traditional habitable zone

Planet Formation

Modeling Accretion Chambers, 2001

Condensation of Volatiles in the Circumstellar Disk

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

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. . .

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. . . 238 U → 234 Th +α (this is nuclear fission (= energy – remember? ))

Consequences of Interior Heating I. Differentiation

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

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

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

Chemical Energy for Life

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

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…

Solar Radiation Budget

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

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

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

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 http: //www. dlr. de/en/desktopdefault. aspx/tabid-5170/8702_read-15322/8702_page-2/

Extras

Terrestrial Impact Frequency Hiroshima year Tunguska century Tsunami danger ten thousand yr. Global “Catastrophic” depends on who you are and where you live. . . catastrophe million yr. “Armageddon” Impact (Texas-sized!) K/T billion yr. 0. 01 (Credit: “Catastrophic” D. Morrison) 1 100 10, 000 million 100 million yield depends. TNT on equivalent who you are and(MT) where you live. . .

Surface-Sterilizing Impacts 0 eating H t c a p Im Ge 1 al rm he ot Depth (km) Heat-Sterilized die a Gr Habitable nt 2 0 100 Temperature (°C) 200 (Sleep & Zahnle, 1998)

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