1. Astronomy 340 Fall 2005
13 October 2005
Class #12

2. Announcements HW #1 being returned today HW #2 due today
Midterm next Thursday (20 October)
Review sheet will be available on line by 3:30 tomorrow afternoon
Expect quantitative problems (e.g. problems 1,2,6,7,8 from HW #1)
Expect some qualitative problems

3. Review – Planetary Atmospheres
Structure of the Atmosphere
Ideal gas law (equation of state)
Hydrostatic equilibrium
Scale height
Energy considerations
Conduction
Radiation
Convection – need steep temperature gradient for the onset of convection
Escape

4. Evolution of Terrestrial Atmospheres
Basic Observations
Earth’s atmosphere isn’t primordial
Terrestrial planets are missing H compounds
Lack of volatiles
Volatiles = H,He,Ar,Kr,Xe,N,F,Cl
H, He should be able to escape
What about the rest?
Sources for atmospheres
Volcanism – produces lots of CO2 on Earth

5. CO2
Earth – most of it resides in rocks in the form of CaCO3 – depleted from atmosphere via rain
Venus
Without H2O there is no mechanism to remove CO2 from atmosphere  CO2 is mostly in the atmosphere
Lack of H2O  increase viscosity of mantle  no convection  no tectonics  rigid “lid”
Mars
No means of releasing CO2 from rocks