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[Fizinfo] Szemináriumi meghívó / Invitation to a seminar

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  • Subject: [Fizinfo] Szemináriumi meghívó / Invitation to a seminar
  • Date: Fri, 04 Nov 2022 15:00:00 +0100
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Szemináriumi meghívó / Invitation to a seminar


Date: Nov 10, 2022 (Thursday) 14:00

Stephen J. Mojzsis (Konkoly Observatory, CSFK, Hungary):
Evolution of planet-forming nuclides and their expression in terrestrial
exoplanet geodynamics

Unlike the Hertzsprung–Russell diagram for stars, there remains no formal
classification for solid exoplanets composed of varying proportions of gas,
rock+metals and ice. Still, as with stars, planetary mass and composition –
expressed in geochemical and cosmochemical terms – mold bulk physical
characteristics. Two physical attributes control terrestrial-type planet
interior dynamics: viscosity (η) and intrinsic heat production (A). Viscosity
can differ by orders of magnitude between different common mantle silicate
minerals (e.g. olivine, pyroxene), so that even small proportional changes
yield large differences to η. A key parameter to consider in this context is
(Mg:Si:Fe), because this value largely determines which minerals will be
present in silicate mantles. Bulk Silicate Earth's (Mg:Si:Fe) is close to
solar values, and we can assume that this also holds for terrestrial-type
exoplanets in that they follow the compositions of their host stars.
Transition between mechani
cally weak (olivine-dominated at (Mg/Si)≤1, low η) vs. strong
(pyroxene-dominated at (Mg/Si)>1, high η) mantle convective regimes occurs
over a narrow transitional range of (Mg/Si) values because small volume
fractions of a weak phase are sufficient to form an interconnected network
that in turn governs the strain response of mantle rocks to deforming
stresses acting upon them. Heat production in younger planets ought to be
greater from more radioactivity and latent accretionary/gravitational heating
vs. older (cooler) ones. This has important consequences for how heat loss is
accommodated by interior dynamics and how it is expressed via outgassing to
secondary atmospheres. Here I show how combining geodynamics with
astrophysical observations provides insights to terrestrial exoplanet η and A
vs. age. Younger (≤2 Gyr) stars tend to have low (Mg/Si)≤1. If these stars
mirror the silicate mantles of their rocky exoplanet companions, we forecast
that such younger low (Mg/Si) py
roxene-rich rocky exo-mantles ought to tend towards both high η and A, with
episodic sluggish/rapid convection and thus slow cooling, and low oxygen
fugacity that degas H2 and CH4 under near-surface partial melting conditions.
Contrariwise, older (>5 Gyr) olivine-rich (high Mg/Si) oxidized (like Earth)
exo-mantles should tend towards both low η and A, effectively cool, and degas
N2, CO2, H2O. By implication, a fundamental age-composition dichotomy is
anticipated to exist between young (hot, reduced, Fe-rich) and old (cold,
oxidized, Fe-poor) rocky exoplanets that can already be evaluated by
mass-radius density-age data. I test, with recent atmospheric retrieval data,
the predictability of such models with an example of an "Ultra-hot Jupiter"
hosted by a Sun-like main sequence star.

The seminar will be held live in the Detre hall with audience, but also
streamed online via Zoom. If you are unable to attend the presentation in
person, The seminar will be held online via Zoom. you can join us via this
or the meeting ID: 828 0691 1982 and passcode: 206265

Everyone is welcome!

Krisztián Vida, Ramon Brasser

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