Mars Global Surveyor
Magnetometer - PI: M. Acuna
Planetary Dynamos
Volume of electrically conducting fluid
... which is convecting 2
... and rotating
All planetary objects
probably have enough
rotation - the presence
(or not) of a global
magnetic field tells us
about
1 and 2
1
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
Neutral
Ion
Bulk removal
“stripping”
Ion pickup
Photochemical loss
Sputtering
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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
Solar wind and magnetic
field impinging on Mars’
complex magnetic field
Close-up of strong anomaly region
David Brain
Changing Topology of Mars’
Magnetic Field
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Over a Strong Magnetic Region
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Mars
Aeronomy
Mission
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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