HR: 0800h
AN: P41C-04    [Abstracts]
TI: Tidal Excitation of the Core Dynamo of Mars
AU: Seyed-Mahmoud, B
EM: seyeb0@uleth.ca
AF: Physics Department, University of Lethbridge, Lethbridge, AB T1K 3M4, Canada
AU: * Arkani-Hamed, J
EM: jafar@physics.utoronto.ca
AF: Department of Physics, University of Toronto, Toronto, ON M5S 1A7, Canada
AU: Aldridge, K
EM: keith@yorku.ca
AF: Graduate Program in Earth and Space Science, York University, Toronto, ON M3J 1P3, Canada
AB: The lack of magnetic anomalies inside the giant impact basins Hellas, Isidis, Utopia and Argyre, inside the northern low lands, over the Tharsis bulge, and over the Tharsis and Olympus mounts suggests that the core field of Mars ceased to exist by about 4 Gyr ago, almost when the giant basins were formed. On the other hand, the giant basins are located on a great circle, implying that the basins were likely produced by fragments of a large asteroid that broke apart as it entered the Roche limit of Mars. This scenario offers a causative relationship for the apparent coincidence of the formation of the giant basins and the cessation of the core dynamo. We suggest that the core dynamo was excited by tidally driven elliptical instability in the Martian core. The breaking of the asteroid and its final impact on Mars eliminated the excitation and thus killed the dynamo. We show that a retrograde asteroid captured in a Keplerian orbit around Mars at a distance of about 50,000-100,000 km could orbit Mars for several hundreds of millions of years before impacting the planet due to the tidal coupling of the asteroid and Mars. Because of relatively very short growth time of the elliptical instability, less than 50,000 years, the asteroid was capable of retaining the elliptical instability and energizing the core dynamo for a geologically long period prior to 4 Ga. Our laboratory observations of a parametric instability of a rotating incompressible fluid, contained in a flexible-walled spherical cavity, confirm the possibility that an early Martian dynamo could have been powered by tidal straining.
DE: 5420 Impact phenomena, cratering (6022, 8136)
DE: 5440 Magnetic fields and magnetism
DE: 6205 Asteroids
DE: 6206 Asteroids: satellites
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Joint Assembly