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Simulating Imaging of Large Scale Radio Arrays on the Lunar Surface
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A long-lived lunar dynamo driven by continuous mechanical stirring.

C A Dwyer1, D J Stevenson, F Nimmo

  • 1Department of Earth and Planetary Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, California 95064, USA. cadwyer@ucsc.edu

Nature
|November 11, 2011
PubMed
Summary

Earth-driven precession may have powered the Moon's ancient magnetic field. This mechanical stirring model explains the long-lasting lunar dynamo and its eventual shutdown as the Moon moved away from Earth.

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Area of Science:

  • Planetary Science
  • Geophysics
  • Astrophysics

Background:

  • Lunar rocks reveal an ancient magnetic field, suggesting a lunar dynamo.
  • Conventional dynamo models struggle to explain the Moon's dynamo's existence and duration.
  • The Moon's magnetic field persisted for over 400 million years.

Purpose of the Study:

  • To investigate mechanical stirring as an alternative lunar dynamo generation mechanism.
  • To model dynamo generation driven by differential motion between the Moon's mantle and core.

Main Methods:

  • Investigated continuous mechanical stirring caused by Earth-driven precession of the lunar spin axis.
  • Modeled fluid motions and power requirements for a dynamo operating over one billion years.
  • Analyzed the generation of a magnetic field with an intensity exceeding one microtesla 4.2 billion years ago.

Main Results:

  • Mechanical stirring readily generates the necessary fluid motions and power for a long-lasting lunar dynamo.
  • The model predicts a magnetic field intensity of over one microtesla 4.2 billion years ago.
  • The lunar dynamo is predicted to shut off naturally as the Moon recedes from Earth.

Conclusions:

  • Mechanical stirring provides a viable mechanism for generating the ancient lunar magnetic field.
  • The dynamo shut off around 2.7 billion years ago when the Moon reached approximately 48 Earth radii.
  • Lunar paleomagnetic data could constrain the early orbital evolution of the Moon and apply to other celestial bodies.