Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p33b1453a&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P33B-1453
Other
1507 Core Processes (1213, 8115), 5420 Impact Phenomena, Cratering (6022, 8136), 5440 Magnetic Fields And Magnetism, 5450 Orbital And Rotational Dynamics (1221), 5499 General Or Miscellaneous
Scientific paper
We first show that 7 out of the 20 giant impact basins of Mars recently reported by Frey [2008] trace a great circle on Mars. The other five basins trace another great circle and still the other three basins trace yet another great circle. The latter great circle is in good agreement with the pre-Tharsis equator of Mars that is estimated from modeling crustal magnetic anomalies and diagonalizing the moment of inertia of Mars after removing the loading effects of Tharsis bulge. It is shown in this paper that the three great circles were likely the equatorial plane of Mars at certain periods and Mars experienced appreciable polar wander. The great circles also indicate that the asteroids that created the basins were satellites of Mars whose orbits decayed in time through spin-orbit coupling with tidally deforming planet, and eventually impacted on Mars creating the giant basins at around 4 Ga. The orbital dynamics of the four largest asteroids show that any of them could have orbited Mars for several hundred million years if it were a retrograde satellite. Continual elliptical straining of otherwise circular fluid streamlines of the liquid core of Mars by tidal deformation could have exerted a strong strain, that was large enough to overcome dissipation and excite the elliptical instability inside the core. We estimate the physical properties of the Martian core that are required to allow the tidal deformation to power the core dynamo. The growth time of the elliptical instability is shorter than the dissipation time. The tidal energy dissipation rate inside Mars is found to be over two orders of magnitude greater than the magnetic energy dissipation rate in the core. It is concluded that even if only one of the 4 largest asteroids were orbiting in retrograde sense, it would have likely powered the core dynamo of Mars for several hundred million years.
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