Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmgp31a..02d&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #GP31A-02
Physics
[1510] Geomagnetism And Paleomagnetism / Dynamo: Theories And Simulations, [1595] Geomagnetism And Paleomagnetism / Planetary Magnetism: All Frequencies And Wavelengths, [5440] Planetary Sciences: Solid Surface Planets / Magnetic Fields And Magnetism, [6250] Planetary Sciences: Solar System Objects / Moon
Scientific paper
Paleointensity data have long been adduced as evidence of an ancient lunar magnetic dynamo and recent paleomagnetic measurements have strengthened this argument [1]. However, a driving mechanism for the dynamo has been hard to find. We investigate here the possibility of a mechanically-stirred dynamo driven by nutation. Nutation results in the stirring of a liquid core by the differential motion of the solid outer mantle. Lunar laser ranging supports a small (≈335 km) liquid core and provides an estimate of the energy dissipated at the lunar core/mantle boundary at the present-day [2]. While the current energy dissipation rate is not enough to power a dynamo, the energy available would have been much larger earlier in lunar history, when the moon was closer to Earth and the spin axis was more offset from the orbital plane. As a first step investigating the feasibility of a nutation-driven lunar paleodynamo, we considered the energy budget likely available to power a dynamo. Model A used a simple scaling argument based on the terrestrial dynamo. Model B was based on the energy flux model of [3]. For lunar semi-major axes less than ≈42 REarth (≈3 Ga), both models produce comparable results and predict surface fields greater than 1 µT (comparable to the paleointensity estimates of [1]). Furthermore, a nutation-driven dynamo would have naturally ceased to operate as the lunar orbit expanded; it would have failed when the available power (which strongly depends on semi-major axis) was no longer able to overcome the tendency of the core to cool to a subadiabatic state. Thus, mechanical stirring via nutation is a viable potential driver of a lunar dynamo and deserves further study. [1] Garrick-Bethell et al. (2009) Science 323, 356-359. [2] Williams et al. (2001) JGR-P 106, 27933-27968. [3] Christensen et al. (2009) Nature 457, 167-169.
Dwyer C. A.
Nimmo Francis
Stevenson Jacob D.
No associations
LandOfFree
An Early Nutation-Driven Lunar Dynamo does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with An Early Nutation-Driven Lunar Dynamo, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and An Early Nutation-Driven Lunar Dynamo will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1501681