ELFT HÍRADÓ

[vidakris AT konkoly.hu]

Szemináriumi meghívó / Invitation to a seminar
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CSFK CSI SZEMINÁRIUM / KONKOLY OBSERVATORY 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 
link
https://us06web.zoom.us/j/82806911982?pwd=SVZpT0syQ1J6dHBvSkF4N2dXNEQ0dz09
or the meeting ID: 828 0691 1982 and passcode: 206265



Everyone is welcome!

Krisztián Vida, Ramon Brasser
organizers
https://konkoly.hu/szeminar/szeminarium.shtml