Astro 120 Fall 2003: Lecture 16 page 1
•Venus
•recent and continued volcanic activity
•strange features: arachnoids, coronae, . . .
•overwhelming atmosphere
•Mars
•Hemisphere dichotomy
•Tharsis Bulge features
•polar caps
•evidence of liquid water
Brief review of last time: Venus and Mars
Reading: Chapter 11, Section 11.1-11.3, 11.5-6, (14.3-14.4)
Midterms submitted: please check with us with grade questions
Astro 120 Fall 2003: Lecture 16 page 2
Overview of Planetar
y
Atmos
p
heres
Text
J
u
p
iter 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, NH4SH NH3, C H 4
Jovians
Venus Earth Mars
Surf. Pressure 92 1 0.007
%CO296 trace 95
%N2477 3
% O2021 0
avg. T [C] 470 15 -50
Clouds H2SO4H2OCO
2 , H2O
Terrestrial
Astro 120 Fall 2003: 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 = 2.1km/s×T
273K×mh
mmol
1/6vesc =1.9km/s×Mplanet
MEarth
×REarth
R
gas will escape if this is greater than 1/6 vesc:
Astro 120 Fall 2003: Lecture 16 page 4
•outgassing (volcanism): release of gas from interior
CO2, N2, H2O, CH4, S O 2
•impacts of icy bodies: H2O, CH4, C O 2
•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
