ORCID Profile
0000-0003-0000-125X
Current Organisations
Research Centre for Astronomy and Earth Sciences
,
University of Colorado at Boulder
,
Eötvös Loránd University
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: EDP Sciences
Date: 24-11-2020
DOI: 10.1051/0004-6361/202038386
Abstract: Context. Long-lived radioactive nuclides, such as 40 K, 232 Th, 235 U, and 238 U, contribute to persistent heat production in the mantle of terrestrial-type planets. As refractory elements, the concentrations of Th and U in a terrestrial exoplanet are implicitly reflected in the photospheric abundances of the stellar host. However, a robust determination of these stellar abundances is difficult in practice owing to the general paucity and weakness of the relevant spectral features. Aims. We draw attention to the refractory, r -process element europium, which may be used as a convenient and practical proxy for the population analysis of radiogenic heating in exoplanetary systems. Methods. As a case study, we present a determination of Eu abundances in the photospheres of α Cen A and B with high-resolution HARPS spectra and a strict line-by-line differential analysis. To first order, the measured Eu abundances can be converted into the abundances of 232 Th, 235 U, and 238 U with observational constraints, while the abundance of 40 K is approximated independently with a Galactic chemical evolution model. Results. Our determination shows that europium is depleted with respect to iron by ~0.1 dex and to silicon by ~0.15 dex compared to solar in the two binary components. The loci of α Cen AB at the low-ends of both [Eu/Fe] and [Eu/Si] distributions of a large s le of FGK stars further suggest significantly lower potential of radiogenic heat production in any putative terrestrial-like planet (i.e. α -Cen-Earth) in this system compared to that in rocky planets (including our own Earth) that formed around the majority of these Sun-like stars. Based on our calculations of the radionuclide concentrations in the mantle and assuming the mantle mass to be the same as that of our Earth, we find that the radiogenic heat budget in an α -Cen-Earth is 73.4 −6.9 +8.3 TW upon its formation and 8.8 −1.3 +1.7 TW at the present day, which is 23 ± 5% and 54 ± 5% lower than that in the Hadean Earth (94.9 ± 5.5 TW) and in the modern Earth (19.0 ± 1.1 TW), respectively. Conclusions. As a consequence, mantle convection in an α -Cen-Earth is expected to be overall weaker than that of Earth (assuming other conditions are the same), and thus such a planet would be less geologically active, suppressing its long-term potential to recycle its crust and volatiles. With Eu abundances being available for a large s le of Sun-like stars, the proposed approach can extend our ability to predict the nature of other rocky worlds that can be tested by future observations.
Publisher: Elsevier BV
Date: 2018
Publisher: American Astronomical Society
Date: 03-2022
Abstract: The bulk chemical composition and interior structure of rocky exoplanets are fundamentally important to understand their long-term evolution and potential habitability. Observations of the chemical compositions of solar system rocky bodies and of other planetary systems have increasingly shown a concordant picture that the chemical composition of rocky planets reflects that of their host stars for refractory elements, whereas this expression breaks down for volatiles. This behavior is explained by devolatilization during planetary formation and early evolution. Here we apply a devolatilization model calibrated with solar system bodies to the chemical composition of our nearest Sun-like stars— α Centauri A and B—to estimate the bulk composition of any habitable-zone rocky planet in this binary system (“ α -Cen-Earth”). Through further modeling of likely planetary interiors and early atmospheres, we find that, compared to Earth, such a planet is expected to have (i) a reduced (primitive) mantle that is similarly dominated by silicates, albeit enriched in carbon-bearing species (graphite/diamond) (ii) a slightly larger iron core, with a core mass fraction of 38.4 − 5.1 + 4.7 wt% (see Earth’s 32.5 ± 0.3 wt%) (iii) an equivalent water-storage capacity and (iv) a CO 2 –CH 4 –H 2 O-dominated early atmosphere that resembles that of Archean Earth. Further taking into account its ∼25% lower intrinsic radiogenic heating from long-lived radionuclides, an ancient α -Cen-Earth (∼1.5–2.5 Gyr older than Earth) is expected to have less efficient mantle convection and planetary resurfacing, with a potentially prolonged history of stagnant-lid regimes.
Publisher: Elsevier BV
Date: 05-2021
Publisher: American Astronomical Society
Date: 05-2023
Abstract: Rocky planet compositions regulate planetary evolution by affecting core sizes, mantle properties, and melting behaviors. Yet, quantitative treatments of this aspect of exoplanet studies remain generally underexplored. We attempt to constrain the range of potential bulk terrestrial exoplanet compositions in the solar neighborhood ( pc). We circumscribe probable rocky exoplanet compositions based on a population analysis of stellar chemical abundances from the Hypatia and GALAH catalogs. We apply a devolatilization model to simulate compositions of hypothetical, terrestrial-type exoplanets in the habitable zones around Sun-like stars, considering elements O, S, Na, Si, Mg, Fe, Ni, Ca, and Al. We further apply core–mantle differentiation by assuming constant oxygen fugacity, and model the consequent mantle mineralogy with a Gibbs energy minimization algorithm. We report statistics on several compositional parameters and propose a reference set of (21) representative planet compositions for use as end-member compositions in imminent modeling and experimental studies. We find a strong correlation between stellar Fe/Mg and metallic-core sizes, which can vary from 18 to 35 wt%. Furthermore, stellar Mg/Si gives a first-order indication of mantle mineralogy, with high-Mg/Si stars leading to weaker, ferropericlase-rich mantles, and low-Mg/Si stars leading to mechanically stronger mantles. The element Na, which modulates crustal buoyancy and mantle clinopyroxene fraction, is affected by devolatilization the most. While we find that planetary mantles mostly consist of Fe/Mg silicates, the core sizes and relative abundances of common minerals can nevertheless vary significantly among exoplanets. These differences likely lead to different evolutionary pathways among rocky exoplanets in the solar neighborhood.
Location: United States of America
No related grants have been discovered for STEPHEN MOJZSIS.