climates of terrestrial planets

Climates of Terrestrial Planets

Dave Brain

LASP / CU Boulder

Do magnetic fields affect planet surfaces?

Do magnetic fields affect atmospheres?

Do magnetic fields affect climate?

An interesting question with no definite answer will be posed here, for you to look at until the lecture actually starts

Approach

Climates Heliophysics

I. Climates

II. Changing Climates

III. Atmospheric Escape Processes

[ Break ]

Heliophysics Climates

IV. External Drivers

V. Internal Drivers

VI. Prospects

I. Climates

Contemporary ClimatesVenus Earth Mars

Surface Temperature

740 K 288 K 210 K

Surface Pressure 92 bars 1 bar 7 mbar

Composition 96% CO2; 3.5% N2 78% N2; 21% O2 95% CO2; 2.7% N2

H2O content 20 ppm 10,000 ppm 210 ppm

Precipitation None at surface rain, frost, snow frost

Circulation1 cell / hemisphere,

quiet at surface but very active aloft

3 cells / hemisphere, local and regional

storms

1-2 cells / hemisphere or patchy circulation, global dust storms

Maximum surface winds

~3 m/s > 100 m/s ~30 m/s

Seasonal Variation

None Comparable northern and southern seasons

Southern summer more extreme

II. Changing Climates

A very exciting question will be asked here•

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Four Ways to Change TSurface

Solar Output Planetary Albedo

Greenhouse Gas Content Planetary Orbital Elements

NASA Ames / J. LaskarRibas et al., 2010

Evidence for Climate ChangeVenus

Matsui et al., 2012

Strom et al., 1994

Evidence for Climate ChangeMars

Geomorphology

Isotopes

Geochemistry

Jakosky and Phillips, 2002

Evidence for Climate ChangeEarth

IceBubbles compositionIsotopes temperaturesPollen conditions

Trees and CoralSeparation growth rate climate

SedimentFossils / pollen conditionsComposition temperatureLayering climate shiftsTexture environment

Atmospheric Source and Loss Processes

Source

Outgassing

Loss

Escape to spaceHydrodynamic escape

Source and Loss

ImpactsSurface exchange

III. Atmospheric Escape Processes

Wow – another question!•

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Requirements for Escape

Escape Energy

Directed Upward

No Collisions

Escape from exobase region

Venus Earth Mars

vesc 10 km/s 11 km/s 5 km/s

E(H+) 0.5 eV 0.6 eV 0.1 eV

E(O) 9 eV 10 eV 2 eV

Reservoirs for Escape

Thermosphere

T(z)

Diffusive equilibrium

V: ~120-250 kmCO2, CO, O, N2

E: ~85-500 kmO2, He, N2

M: ~80-200 kmCO2, N2, CO

Exosphere

“collisionless”

Ballistic trajectories

V: ~250-8,000 kmH

E: ~500-10,000 kmH, (He, CO2, O)

M: ~200-30,000 kmH, (O)

Ionosphere

Small % of neutrals

Incident energy forms peaks

V: ~120-300 kmO2

+, O+, H+

E: ~75-1000 kmNO+, O+, H+

M: ~80-200 kmO2

+, O+, H+

Lots of red here

(I got tired)

Sur

face

Spa

ce

Terrestrial Planet Magnetospheres

Intrinsic Magnetosphere Induced Magnetosphere

Cartoons courtesy S. Bartlett

Escape Processes

Neutral Particle Processes

Jeans Escape (E,M)

Photochemical Escape (V,M)

O2+ + e- O* + O*

Sputtering (V, M)

Charged Particle ProcessesIon pickup (V,M)

Ion outflow (V,E,M)

Bulk plasma escape (V,M)

Moore et al., 1999

Luhmann and Kozyra, 1991

Alternative Classification Scheme

• Electric fields accelerate charged particles

• Can loosely identify pickup, Hall, and pressure gradient escape

• Highlights that combinations of mechanisms can accelerate ions

Pickup Hall Electron Pressure Gradient