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Lec 22: 16 Nov 2011 Chap 9 & 11: Atmosphere, Hydrosphere, and Climate LAST TIME - Terrestrial Planets. I. •  Geology of Mercury, Venus, and Mars •  Ancient Water on Mars

TODAY - Effects of Water and Atmospheres •  Atmospheres of Terrestrial Planets •  The Greenhouse Effect

NEXT - Terrestrial Planets and Life •  Goldilocks and the 3 Planets •  Climate Change and Human Impacts •  Life Beyond Earth?

Earth’s Atmosphere

•  COMPOSITION – N2 (Nitrogen) 78.1% (relatively inert) – O2 (Oxygen) 20.9% (highly reactive) – H20 (water vapor) 0.01% to 3% – Ar 0.93% – CO2 (carbon dioxide) 0.034% (increasing) – Ne (Neon) 0.0018% – He (Helium) 0.0005% – CH4 (methane) 0.0002% (increasing)

•  STRUCTURE – Troposphere -> Tropopause – Stratosphere -> Stratopause – Mesosphere -> Mesopause –  Ionosphere (thermosphere)

– Troposphere contains all of the “weather” –  density drops with altitude (1/2 as dense at 5.5 km)

–  humidity drops with altitude (1/2 as humid at 2 km)

–  temperature decreases with altitude (6o C per km) in the troposphere but increases with altitude in stratosphere!

Ozone molecules in the stratosphere absorb ultraviolet light

Ozone Layer

In this ultraviolet photo, you can see the clouds of Venus. The clouds are featureless in visible light

The upper cloud layers move rapidly around the planet in a retrograde direction, with a period of only about 4 Earth days (remember the planet rotates very slowly).

The surface temperature is about the same everywhere, pole to equator, front to back!

Pioneer-Venus View of Venus in the Ultraviolet Global Dust Storms on Mars

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Interactions between atmosphere and surface of Mars

Water on the Surface of Mars (continued) •  Polar Caps

– part permanent, part seasonal (like Earth’s) – water ice and dry ice (CO2) – Southern Cap

•  always < 150 K; smaller permanent cap; probably only a few meters thick

– Northern Cap •  warmer (above CO2 freezing point); larger permanent

cap; definitely water ice; more embedded dust – Global permafrost linked to caps – Atmosphere linked to caps

Atmospheres of the Terrestrial Planets

•  What kind of gas?

•  How much gas? – Venus 90 times Earth – Mars 1/100th of Earth

•  Surface winds; sluggish and steady on Venus; seasonal on Mars (e.g. global dust storms)

•  Weather and erosion (no precipitation on Venus or Mars)

•  Where does the gas come from? go to? – Sources? – Sinks?

•  Earth’s atmosphere... – originally H, He, CH4, NH3, H2O, CO2 –  early losses: gravity (escape), impacts –  if oceans evaporated, Pressure of water vapor

alone would be 300 bars!! – 60 times more CO2 in oceans than in

atmosphere (rest tied up in carbonates) – SOURCES? SINKS?

•  impacts? •  impacts?

•  outgassing (volcanoes, hydrosphere, crust)

•  absorbed in hydrosphere, biosphere

•  returned to mantle at subduction zones

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Global Properties of the Terrestrial Planets

Mercury Venus Earth Moon Mars

Mass 0.06 0.82 1 0.01 0.11 Diameter 0.38 0.95 1 0.27 0.53 Density (g/cc) 5.4 5.2 5.5 3.3 3.9 uncompressed... 5.2 4.3 4.4 3.3 3.8

Gravity 0.38 0.91 1 0.17 0.38 Albedo (%) 12 59 39 11 15 Atm. Pressure 0 88 1 0 0.01 Temperature (degrees K)

103-623

733 183-333

93- 403

133- 293

Temperatures of Terrestrial Planets

•  Equilibrium Temperature Without Atmosphere: Venus 325 K, Earth 250 K, Mars 210 K

•  Actual Temperatures: Venus 740 K, Earth 290 K, Mars 240 K

•  Is CO2 the culprit? – many molecules absorb infrared – CO2 is worse than water, but many others are

worse than CO2 (e.g. CH4, HCFC’s)

Earth’s Hydrosphere •  enough water to cover entire surface to depth of about 3

km •  but ‘only’ 71% is covered with liquid water

–  oceans very deep; continents very tall –  “RELIEF”

•  RESERVOIRS –  oceans (97.3%) –  glaciers & polar caps (2.1%) –  groundwater (0.6%) –  lakes and rivers (0.01%) –  atmosphere (0.001%) –  biosphere (0.0004%)

•  COMPOSITION of seawater includes: –  dissolved solids

•  “salts” (3.5% by mass) [Cl, Na, Mg, S, Ca, K] •  where does the salt come from? [hint: water is an

excellent solvent] •  where does it go? [must be continually removed;

otherwise oceans would be full of salt after only about 1 million years!]

–  dissolved gasses •  e.g. oxygen, carbon dioxide •  oceans contain 60 times more carbon dioxide than the

atmosphere!

•  CIRCULATION –  oceans are well mixed

•  equator to pole •  top to bottom

–  salt sources and sinks

•  INTERACTIONS –  complex couplings between ocean, atmosphere,

crust, and biosphere [I’ll be pointing out examples of these...]

–  coupling between polar caps and sea level

•  Liquid water is essential for life [why?] •  Fresh water is essential for human life