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(2020) How has Galactic Chemical Evolution Affected Terrestrial Planet Composition and Tectonics?

O'Neill C


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01a: Room 1, Tuesday 23rd June 06:45 - 06:48

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Submitted by Larry Nittler on Monday 22nd June 19:23
interesting presentation. I can't be up at 2 am my time for the live Q&A, so I'll ask my question here. We see huge range of core sizes in the rocky planets of our solar system (compare Mercury and Earth) but both formed form a star with a single Fe/Si ratio. This shows that substantial fractionation processes can occur during planet building. Given this, what is the justification for assuming that stellar composition (Fe/Si) translates directly to planet core size?
Great Q Larry. The work here is definitely dealing with population trends. The solar system has examples of large (Mercury) and small (Moon) core bodies, and there appears to be a lot of stochastic and other effects in play (impacts, scattering, grain migration etc). The assumption here is that over a large population (eg. exoplanet catalogues) these stochastic effects average out, and broader trends becpme evident. So here, purely for expediency, we assume an Earth:Solar System element partitioning, holding that as a (poorly known) constant, and compare planetary variations due to that trend. It may be that the stochastic effects are of a similar magnitude to the effects we see, and we get a wide range of planets over the galaxy's evolution, but my feeling is the effects of GCE elemental changes would induce a shift in the geodynamics of these populations, given what we see in the models.

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