Giant Impact Stratification of the Martian Core

Details Giant Impact Stratification of the Martian Core Giant Impact Stratification of the Martian Core

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p31c1255a&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P31C-1255

Physics

[1510] Geomagnetism And Paleomagnetism / Dynamo: Theories And Simulations, [5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [5440] Planetary Sciences: Solid Surface Planets / Magnetic Fields And Magnetism, [5499] Planetary Sciences: Solid Surface Planets / General Or Miscellaneous

Scientific paper

We investigate the direct thermal effects of a giant impact on the Martian core and its dynamo. Impact heating of the core is calculated assuming a final impact basin of 6000 km diameter, a 10 km/s impact velocity, and a 30% impact energy to impact heating ratio. The spherical shock wave propagates from the impact site and impinges the spherical surface of the liquid core, where it partly reflects back to the mantle and partly enters the core. The impact heating of the core is largest at the core-mantle boundary and the sub-impact point, but it decreases in the interior. Assuming the core was initially close to a well-mixed state with a convection-driven dynamo, the non-uniform impact heating produces an overturn event leading to a strong stable thermal stratification, which is calculated assuming the re-distribution process is fast and therefore adiabatic. Dynamo models show that a pre-existing magnetic field decays within less than 20 Kyr following the impact, and calculations of the subsequent core cooling suggest that a convection-driven dynamo may not resume for several hundred million years.

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