Habitable Zones & Global Climate

Distribution of Europium in The Milky Way Disk; Its Connection to Planetary Habitability and The Source of The R-Process

By Keith Cowing

Status Report

astro-ph.SR

December 2, 2024

Filed under astro-ph.SR, dwarf stars, europium, exoplanet, habitability, Habitable Zone, metallicity, metallicity Goldilocks zone, thorium, uranium

Distribution of Europium in The Milky Way Disk; Its Connection to Planetary Habitability and The Source of The R-Process — Illustration similar to that of Fig. 2 in Nimmo et al. (2020), demonstrating the sensitivity of core convection to changing concentrations of radiogenic elements (relative to the terrestrial amount), see Nimmo et al. (2020) for details on model parameters. Color scaled to represent net entropy production from radiogenic heating, with the black region representing negative production (no dynamo). Dashed red line represents the regime at [Eu/α]=0.08 where a dynamo failure lasting > 100 Myr first begins. Solid black lines represent contours of constant mantle temperature. astro-ph.SR

The energy provided in the radioactive decay of thorium (Th) and uranium (U) isotopes, embedded in planetary mantles, sustains geodynamics important for surface habitability such as the generation of a planetary magnetic dynamo.

In order to better understand the thermal evolution of nearby exoplanets, stellar photospheric abundances can be used to infer the material composition of orbiting planets. Here we constrain the intrinsic dispersion of the r-process element europium (Eu) (measured in relative abundance [Eu/H]) as a proxy for Th and U in local F, G, and K type dwarf stars. Adopting stellar-chemical data from two high quality spectroscopic surveys, we have determined a small intrinsic scatter of 0.025 dex in [Eu/H] within the disk.

We further investigate the stellar anti-correlation in [Eu/α] vs [α/H] at late metallicities to probe in what regimes planetary radiogenic heating may lead to periods of extended dynamo collapse. We find that only near-solar metallicity stars in the disk have Eu inventories supportive of a persistent dynamo in attendant planets, supporting the notion of a “metallicity Goldilocks zone” in the galactic disk.

The observed anti-correlation further provides novel evidence regarding the nature of r-processes injection by substantiating α element production is decoupled from Eu injection. This suggests either a metallicity-dependent r-process in massive core-collapse supernovae, or that neutron-star merger events dominate r-process production in the recent universe.

Evan M. Carrasco, Matthew Shetrone, Francis Nimmo, Enrico Ramirez-Ruiz, Joel Primack, Natalie M. Batalha

Comments: 11 pages, 4 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2411.10711 [astro-ph.SR] (or arXiv:2411.10711v1 [astro-ph.SR] for this version)
https://doi.org/10.48550/arXiv.2411.10711
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Submission history
From: Evan Carrasco M
[v1] Sat, 16 Nov 2024 05:53:00 UTC (3,321 KB)
https://arxiv.org/abs/2411.10711

Astrobiology

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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