2023/09/29 by Ji Wang, Wang, Ji · 5 citations
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Earth and Planetary Astrophysics (astro-ph.EP) #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR) #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2310.00088
openalex publication_date 2023/09/29 · openalex created_date 2023/10/04 · openalex updated_date 2026/07/28
As the number of planetary mass objects (PMOs, \lessapprox13 M_\rmJupiter) at wider separation (\gtrapprox10 AU) grows, there is emerging evidence that they form differently from their higher-mass brown-dwarf (BD) counterparts. Specifically, PMOs' atmospheres are often enriched by metals and show a large dispersion of metallicity, which is usually interpreted as a sign of solid accretion. As a first step toward a population-level study of the amount and timing of solid accretion, we analyze a sample of seven directly-imaged exoplanets with measured stellar and planetary chemical abundances (51 Eri b, β Pic b, HIP 65426 b, HR 8799 c and e, AF Lep b, and YSES 1 c). Our analysis uses existing data of stellar and planetary atmospheric metallicities, and adopts a Bayesian framework that marginalizes the probabilities of disk conditions, formation locations, planetary interior structures, and accretion physics. We show that these PMOs accrete large amounts of solids regardless of whether they form via core accretion or disk instability. On average \gtrapprox50 M_⊕ solids are accreted to enrich planet atmospheres. Individual planet accretes between 23.3 and 223.2 M_⊕ of solid mass, more than 75% of which is assumed to stay in the atmosphere and increase the observed metallicity. The result implies that the solid accretion process and therefore the planet formation process likely take place at an early stage (\lessapprox2 Myr) when large amounts of solids are available in young massive protoplanetary disks.