Astronomy 340 Fall 2005 13 October 2005 Class #12

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

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

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

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