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

Abstract

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/$\alpha$] vs [$\alpha$/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 $\alpha$ 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.

11 pages, 4 figures

References in corpus (22)

• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Swope Supernova Survey 2017a (SSS17a), the Optical Counterpart to a Gravitational Wave Source
• Galactic chemical evolution: Carbon through Zinc
• Mass-Radius Relationships for Solid Exoplanets
• alpha-, r-, and s-process element trends in the Galactic thin and thick disks
• Revisited Mass-Radius relations for exoplanets below 120 Earth masses
• Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program II: Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd and Eu
• The History of R-Process Enrichment in the Milky Way
• The temporal evolution of neutron-capture elements in the Galactic discs
• A new delay time distribution for merging neutron stars tested against Galactic and cosmic data
• The mass-radius relation of exoplanets, revisited
• Nucleosynthesis and observation of the heaviest elements
• Thermal and compositional stratification of the inner core
• Further evidence that galaxy age drives observed type Ia supernova luminosity differences
• Constraining Collapsar r-Process Models through Stellar Abundances
• Radiogenic Heating and its Influence on Rocky Planet Dynamos and Habitability
• Thermal Evolution and magnetic history of rocky planets
• Magnetically-Driven Neutron-Rich Ejecta Unleashed: Global 3D Neutrino-General Relativistic Magnetohydrodynamic Simulations of Collapsars Probe the Conditions for r-process Nucleosynthesis
• Europium as a lodestar: diagnosis of radiogenic heat production in terrestrial exoplanets
• Constraints on the frequency and mass content of r-process events derived from turbulent mixing in galactic disks
• Enrichment of the Galactic disc with neutron-capture elements: Gd, Dy, and Th