GEO 330 Lecture Notes - Lecture 23: Plain, Alba Mons, Isidis Planitia
9 Apr 2018
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Document Summary
Differentiation of mars: as we"ve already discussed, mars has differentiated into a core, mantle, and crust, core radius thought to be ~1300-1500km (compared to total planetary radius of 3396km, timing of core formation constrained by 182hf-182w isotope system. 182hf decays into 182w with a half-life of 9my. W is siderophile element, while hf is not. Large impacts melted crust, destroying anomalies, and when it resolidified, there was no. Timing of large impacts is uncertain but, based on analogies to the moon, probably magnetic field formed between 3. 8 and 4. 0ga. Thus, magnetic field must have shut off by 4ga: magnetic field generated by convection of molten core, loss of magnetic field probably due to planet cooling and solidification of molten part of core. Transition especially abrupt around isidis: crater density difference is somewhat misleading -- noachian and pre-noachian crust lies just below the surface in the southern lowlands.
