Lunar Magnetic Anomalies

Lunar Magnetic Anomalies
Arianna Sorba
Student Number: 14R55018
Home Institution: Imperial College London
Academic Advisor: Prof. Hideo Tsunakawa
Department of Earth and Planetary Sciences
Background
•  Unlike Earth, the moon now has no global magnetic field
•  However, small spot-like magnetic fields are detected by lunar
satellites – lunar magnetic anomalies
•  Anomalies suggest remanent magnetisation of lunar crust
à Possibly caused by an ancient dipolar magnetic field
3-4 billion years ago
•  Most likely generated by ancient core dynamo, which puts
constraints on formation and evolution of Earth-Moon system
•  Size of lunar core
•  Lunar rotation axis
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Research Method
•  I analysed 7 isolated anomalies
à to make judgments about a
possible ancient dipolar magnetic field
•  Each anomaly was approximated by a
dipole source buried in the lunar crust,
and dipole parameters (location,
magnitude, orientation, pole position)
were calculated as an inverse problem
•  Pole positions compared to recent
previous results (Takahashi et al. 2014)
RGS
LM2
LM1
LM4
Nearside
Radial
North
East
LM5
LM6
Farside
LM3
nT
−100 −80 −60 −40 −20
0
20
40
60
80
100
Map of the radial magnetic field at the
lunar surface, measured by Kaguya and
Lunar Prospector satellites
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Takahashi et al. 2014 Results
Analysed 24 anomalies, found 2 clusters: ancient dipole with wander event P2 à P1
90°N
45°N
P2
0°E
90°E
0°N
180°E
-45°N
P1
Takahashi et al. poles
90°N
270°E
360°E
Analysis (LM4 example)
Iterative inversion method (Kurata et al. 2005) used in Fortran to
find best fit dipole model for the observed magnetic field data
NORTH
EAST
TOTAL
r = 0.8470
r = 0.8933
r = 0.8217
r = 0.9642
Model Fields
Observed Data
RADIAL
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Results
3 distinct clusters, agreeing with Takahashi et al. 2014 plus anomaly
90°N
LM3 1
45°N
LM3 2
P2
0°E
LM4
Anomaly poles
90°E
RGS 2
P3
RGS 1
Takahashi et al. poles
LM1
P1
0°N
180°E
LM6
LM2
270°E
LM5
360°E
Conclusions
•  7 isolated lunar magnetic anomalies were analysed
and well-fitted by one or two remanent dipole sources
•  3 distinct clusters, broadly agrees with Takahashi et
al. including outlier
•  Suggests an ancient lunar dipole, undergoing one or
more polar wander events
•  Analysis of more isolated and lineated anomalies
needed to corroborate
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Thank you TokyoTech!
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