Synopsis: Leading to Exploring Other worlds
Atmospheric Processes Karen J. Meech, Astronomer Institute for Astronomy
Applications: Two Physical Effects Earth is a Complex System !
Ozone Hole ! !
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UV creates and destroys O3 in atm Natural balance disturbed by manmade chemicals
Green House Effect ! !
Energy has to get to Earth’s surface Heat (IR) is blocked by atm " causes an increase in T !
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Interdisciplinary approach needed Don’t understand all feedback systems Models only as good as data
What are Implications for our “space ship”?
Why did 2 worlds evolve on different paths? ! Venus – once had oceans !
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Runaway Greenhouse
Mars – once had liquid H2O !
Global cooling
Mars Moon Phobos
Synopsis: Leading to Exploring Other worlds
Atmospheres Outline Purpose
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Surface Features Endogenic Processes !
Clues to interior processes ! !
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Heat loss mechanism Volcanos & tectonics
Interaction with surface !
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Mountains / peaks / ridges Cracks, trenches Plains Causes: plate motion, volcanos, planetary shrinking, expansion . . . .
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Recycling of materials
What can we tell about a world & its potential for life just from its surface features?
Understand what effect an atmosphere has on a planet Understand how to recognize that there is an atmosphere (now and in the past) Understand the typical atmospheric structure Understand that atmospheres change with time (physically and chemically – and why)
Content
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History and comparison of Terrestrial Planet Atmospheres Atmospheric Structure & Composition Aeolian (Wind Driven) Processes
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Some Examples
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Mars Surface (art)
Of or pertaining to an atmosphere (winds and liquids)
Jupiter’s moon Europa Surface
Mercury Surface Features from Earth
Mercury !
Pre-spacecraft data !
0.4 AU from sun
28o max solar elongation ! 19th century images features not real !
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Radar images ! !
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Early – not much detail (size of planet) New – ice (!) at polar cap
Space Era ! ! !
Images: craters/tectonics Magnetosphere Thin atmosphere
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1991& 1994 Earth Radar data ! ! !
Bright reflections Coincide with Mariner 10 dark craters Hints at ice
Science " Public
Venus
1932
CO2 discovered (spectra). H2O had been assumed
1941
Greenhouse effect? " hot surface
1955
Early H2O oceans + liquid hydrocarbons; UV photodissociation " oceans of crude oil
1955
Surface cool; oceans of H2O & carbonic acid (H2CO3)
1961
Large 600K global desert w/strong winds (frictional heating)
1962
Sagan revives Greenhouse effect
1964
Planet accreted hot & dry – never had water
1960 Hot, deadly
1865 Getting there
1943 1954 1959 Hot, desert, habitable Warm & swampy Like precambrian Earth
1965 Warm Early Earth
2000 Hellish
2011 Earth’s Future?
Mars !
Early Earth Observations ! ! ! !
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Lowell Observatory !
Artist impression
Schiaparelli (1877) & Antoniadi (early 1900s) Observations of channels " canals Distinct albedo changes Vegetation? For “Astrobiology”!
Venera 13, 1982
Lowell Observatory
Basic Atmospheric Structure !
Extent of Atmosphere ! !
There is no “edge” to an atm Scale Height (H) !
Density
Distance over which atm density decreases by 1/3 (1/e)
! Earth’s
H = 8.4 km Height
H = kT / (µmH)g
k T µ mH g
= a constant (boltzman) = Temperature [K] = avg atomic weight of molecules (relative to mass of Hydrogen) = mass of Hydrogen = planet s gravity
Examples of Scale Heights (H) Planet Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto
Composition He, Na CO2 N2, O2, Ar CO2, N2 H, He H, He H, He H, He CH4
T [K] 440 730 290 220 128 71 56 47 38
µ! 4 44 29 44 2 2 2 2 16
g [m/s2] H [km] 3.7 245 8.9 15.4 9.8 8.4 3.7 11.2 24.8 21.3 10.4 28.2 8.5 27.2 10.8 18.0 0.8 45
Atmospheric Structure – Earth
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N2 (78%), O2 (20%), Ar (0.9%), water (traces)
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Pressure !
1 atm = 1 bar = 14.7 lbs/in2
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200 250 Temperature [K]
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Ionosphere
T increase: O3
Gases thin Solar wind heating ! Location of aurorae
300
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Composition
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Chemically active gases
From Messenger
Mariner 10: H2 (22%), He (6%), O2,(42%) From Earth: Na (29%), K (0.5%)
Pressure: Sources
Mesosphere
Venusian Atmosphere
Mercury Early Measurements !
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Small "T, smooth flow " airplanes
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Stratosphere
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Earth Main Gases
Weather (lg "T " convection) ! Greenhouse !
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Troposphere !
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T = avg. surface temperature, µ = avg. molecular wt of gases; g = gravity acceleration!
Atmospheric Composition
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10-12 bar
Solar wind (H2 and He) Surface sputtering (O2) Meteroid impact (Na, K)
HF – hydrofluoric acid HCl – hydrochloric acid HSO3F – fluorosulfuric acid
Location P [bar]
T [K]
Wind
Comp
Surface
730
Calm
orange 2/3 ton in2 (4x deep sea)
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30-50km
10-1
500-300
hazes Clouds Top: CO2 & N2, CO, H2O, SO2,
50-70km
HCl. H2SO4 drops " acid rain
103 km/hr
News - CH4 on Mars !
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CO2 (95%), N2 (2.7%), Ar (1.6%), CO, H2O, O2 (
