Mars Global SurveyorMagnetometer - PI: M. Acuna

Planetary DynamosPlanetary Dynamos

Volume of electrically conducting fluid ... which is convecting ... and rotating

All planetary objects probably have enough rotation - the presence (or not) of a global magnetic field tells us about

21

21 and

No core dynamo today

Magnetization of surface rocks

Magnetization only of old, cratered terrain -> Dynamo ceased ~3.5 billion years ago

Ionosphere

Atmospheric Loss Processes

NeutralNeutralIonIon

Bulk removal“stripping”

Ion pickup

SputteringPhotochemical loss

Crustal magnetic sources affect these processes:

shielding atmosphere from SW field topology open field lines

MGS Measurements - Implications

for Mars’ Atmosphere

• Ancient dynamo-> early protection for atmosphere

• Strong crustal magnetization-> affect atmospheric loss after dynamo turn-off

Solar Wind Interaction Boundary

Pressure Balance: obstacle

to the solar wind

PSolar Wind =

P (magnetic)crust

+ P (thermal)ionosphere

David Brain

Mars’Interaction Boundary Response to the Solar Wind

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Field Topology

David Brain

Solar wind and magnetic field impinging on Mars’ complex magnetic field

Close-up of strong anomaly region

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Changing Topology of Mars’ Magnetic Field

Over a Strong Magnetic Region

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Mars Aeronomy Mission

Upper atmosphere Ionosphere Magnetic Field Pick-Up Ions Solar Wind

3 scenarios for how the dynamo stopped

• Dynamo convection driven by radiogenic / formation heating: Cools down, mantle slows down, core stops convecting

• Inner core condensation drives dynamo: Cools down, inner solid core expands to (almost) fill core

•Plate tectonics drives dynamo: Cools down, mantle slows down, core slows down