Plausible Constraints on the Range of Bulk Terrestrial Exoplanet Compositions in the Solar Neighborhood

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 (<200 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.

New Mass and Radius Constraints on the LHS 1140 Planets: LHS 1140 b Is either a Temperate Mini-Neptune or a Water World

“…Moreover, this model converges to a larger mass and smaller radius than observed (2.3σ offset in density). We argue that the inconsistency with the observations coupled with the challenge of forming highly iron-depleted (coreless) planets (Carter et al 2015;Scora et al 2020;Spaargaren et al 2023) make this scenario implausible for LHS 1140 b. This conclusion is in line with exoplanet demographics (Rogers 2015) and the empirical rocky-togaseous transition around M dwarfs (Cloutier & Menou 2020) that most ∼1.6 R ⊕ exoplanets are not rocky.…”

Precise Transit Photometry Using TESS: Updated Physical Properties for 28 Exoplanets around Bright Stars

“…These updated parameter values, as discussed above, are more precise for most of the cases compared to the previous studies, as well as more accurate and reliable. In the present era of large-scale studies in the field of exoplanet science, these updated values of physical properties of several known exoplanets would be immensely useful in a plethora of different studies, starting from the studies of planetary evolution and dynamics (e.g., Boley et al 2020;Petrovich et al 2020;Hamer & Schlaufman 2022;Rozner et al 2022;Vissapragada et al 2022), to their compositional studies (e.g., O'Neill et al 2020;Berardo & de Wit 2022;Edwards & Tinetti 2022;Spaargaren et al 2023), and the search for planetary companions, such as exomoons (e.g., Forgan & Kipping 2013;Trani et al 2020;Saha & Sengupta 2022;Tokadjian & Piro 2023), etc. This study also demonstrates how large-scale survey missions of future can shape our understanding of existing planetary populations even further.…”

Setting the Stage for the Search for Life with the Habitable Worlds Observatory: Properties of 164 Promising Planet-survey Targets

“…According to geochemical models, planets with low Mg/Si ratios tend to cool slowly because their mantle viscosity is high and they may therefore quickly lose their volatiles (Spaargaren et al 2020). Additionally, different Mg/Si ratios shift the condensation sequence of solid planetbuilding blocks, with lower Mg/Si ratios leading to mechanically stronger mantles and higher Mg/Si leading to weaker mantles (Jorge et al 2022;Spaargaren et al 2023). This can carry important consequences for lithosphere dynamics (i.e., plate tectonics, volcanism, etc.…”