Astro 120 Fall 2005: Lecture 16 page 1
•Mars
•General properties: size, orbit, moons
•Hemisphere dichotomy
•Tharsis Bulge features, volcanos and tectonics
•climate changes?
•evidence of liquid water
•results from Mars Exploration Rovers
Brief review of last time: Mars
Reading: Chapter 11, Section 11.1-11.3, 11.5-6, (14.3-14.4)
Midterms posted on WebCT: please check with us with grade questions
Observing Session: Tomorrow (if clear - stay tuned to the website)
Astro 120 Fall 2005: Lecture 16 page 2
Overview of Planetary Atmospheres
Jupiter
Saturn
Uranus
% H
75
85
74
% He
24
14
24
%CH4
< 0.1
< 0.1
< 1
% NH3
< 0.1
< 0.1
< 0.1
avg. T [C]
-150
-185
-210
Clouds
NH3, H2O, ?
NH3, NH4 SH
NH3, CH4
Jovians
Venus
Earth
Mars
Surf. Pressure
92
1
0.007
%CO2
96
trace
95
%N2
4
77
3
% O2
0
21
0
avg. T [C]
470
15
-50
Clouds
H2SO4
H2O
CO2 , H2O
Terrestrial
Astro 120 Fall 2005: Lecture 16 page 3
•Primordial Atmosphere composition:
•mostly H2, He
•trace elements tied up in molecules
!!CO2, CH4, N2, H2O, NH3
•Hydrogen largely lost from inner planets very early:
Planetary Atmospheres: gas, vapor, ice
av.mol.speed = 2.1 km/s×!T
273K×mh
mmol
1/6vesc = 1.9 km/s×!Mplanet
MEarth
×REarth
R
gas will escape if this is greater than 1/6 vesc:
Astro 120 Fall 2005: Lecture 16 page 4
•outgassing (volcanism): release of gas from interior
!!CO2, N2, H2O, CH4, SO2
•impacts of icy bodies: H2O, CH4, CO2
•chemistry
•O2 bound up in oxides (very fast)
•CO2 bound up in carbonate rocks, surface H2O
•H2O bound up in rock
•geology
•H2O trapped beneath surface (permafrost)
•BIOLOGICAL ACTIVITY:
•photosynthesis: CO2 —> O2; methane from cows
•Human Activity
!!CO2, complex organics, CFCs, ozone depletion
Secondary Atmosphere alteration
