Context. Recent years have seen building evidence that planet formation starts early, in the first ~0.5 Myr. Studying the dust masses available in young disks enables us to understand the origin of planetary systems given that mature disks are lacking the solid material necessary to reproduce the observed exoplanetary systems, especially the massive ones. Aims. We aim to determine if disks in the embedded stage of star formation contain enough dust to explain the solid content of the most massive exoplanets. Methods. We use Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 (1.1–1.3 mm) continuum observations of embedded disks in the Perseus star-forming region together with Very Large Array (VLA) Ka-band (9 mm) data to provide a robust estimate of dust disk masses from the flux densities measured in the image plane. Results. We find a strong linear correlation between the ALMA and VLA fluxes, demonstrating that emission at both wavelengths is dominated by dust emission. For a subsample of optically thin sources, we find a median spectral index of 2.5 from which we derive the dust opacity index β = 0.5, suggesting significant dust growth. Comparison with ALMA surveys of Orion shows that the Class I dust disk mass distribution between the two regions is similar, but that the Class 0 disks are more massive in Perseus than those in Orion. Using the DIANA opacity model including large grains, with a dust opacity value of κ9 mm = 0.28 cm2 g−1, the median dust masses of the embedded disks in Perseus are 158 M⊕ for Class 0 and 52 M⊕ for Class I from the VLA fluxes. The lower limits on the median masses from ALMA fluxes are 47 M⊕ and 12 M⊕ for Class 0 and Class I, respectively, obtained using the maximum dust opacity value κ1.3 mm = 2.3 cm2 g−1. The dust masses of young Class 0 and I disks are larger by at least a factor of ten and three, respectively, compared with dust masses inferred for Class II disks in Lupus and other regions. Conclusions. The dust masses of Class 0 and I disks in Perseus derived from the VLA data are high enough to produce the observed exoplanet systems with efficiencies acceptable by planet formation models: the solid content in observed giant exoplanets can be explained if planet formation starts in Class 0 phase with an efficiency of ~15%. A higher efficiency of ~30% is necessary if the planet formation is set to start in Class I disks.

We present a model of the early chemical composition and elemental abundances of planetary atmospheres based on the cumulative gaseous chemical species that are accreted onto planets forming by core accretion from evolving protoplanetary disks. The astrochemistry of the host disk is computed using an ionization driven, nonequilibrium chemistry network within viscously evolving disk models. We accrete gas giant planets whose orbital evolution is controlled by planet traps using the standard core accretion model and track the chemical composition of the material that is accreted onto the protoplanet. We choose a fiducial disk model and evolve planets in 3 traps -water ice line, dead zone and heat transition. For a disk with a lifetime of 4.1 Myr we produce two Hot Jupiters (M = 1.43, 2.67 M Jupiter , r = 0.15, 0.11 AU) in the heat transition and ice line trap and one failed core (M = 0.003 M Jupiter , r = 3.7 AU) in the dead zone. These planets are found with mixing ratios for CO and H 2 O of 1.99 × 10 −4 , 5.0 × 10 −4 respectively for both Hot Jupiters. Additionally for these planets we find CO 2 and CH 4 , with mixing ratios of 1.8 × 10 −6 → 9.8 × 10 −10 and 1.1 × 10 −8 → 2.3 × 10 −10 respectively. These ranges correspond well with the mixing ratio ranges that have been inferred through the detection of emission spectra from Hot Jupiters by multiple authors. We compute a carbon-to-oxygen ratio of 0.227 for the ice line planet and 0.279 for the heat transition planet. These planets accreted their gas inside the ice line, hence the sub-solar C/O.

The detection of Earth-size exoplanets around low-mass stars -such as Proxima Centauri b and the TRAPPIST-1 system-provide an exceptional chance to improve our understanding of the formation of planets around M stars and brown dwarfs. We explore the formation of such planets with a population synthesis code based on a planetesimal-driven model previously used to study the formation of the Jovian satellites. Because the discs have low mass and the stars are cool, the formation is an inefficient process that happens at low periods, generating compact planetary systems. Planets can be trapped in resonances and we follow the evolution of the planets after the gas has dissipated and they undergo orbit crossings and possible mergers. We find that planet formation in the planetesimal accretion scenario is only possible around stars with masses M 0.07M sun and discs of M disc 10 −2 M sun . Hence, in order to form planets (M p 0.1M ⊕ ) around low-mass stars (0.05 M 0.25M sun ), relatively massive discs are required. Our results show that one third of the synthetic planetary systems have at least one planet with M p 1M ⊕ , but we are not able to form planets larger than 5M ⊕ , showing that planets such as GJ 3512b form with another, more efficient mechanism. We find that the large majority of the planets formed have a large water content and most of our synthetic planetary systems have 1, 2 or 3 planets, but planets with 4,5,6 and 7 planets are also common, confirming that compact planetary systems with many planets should be a relatively common outcome of planet formation around small stars. Our results provide information to guide current and future surveys and aid in the interpretation of TESS and PLATO data.

Combining a time-dependent astrochemical model with a model of planet formation and migration, we compute the carbon-to-oxygen ratio (C/O) of a range of planetary embryos starting their formation in the inner solar system (1–3 AU). Most of the embryos result in hot Jupiters (M ≥ MJ, orbital radius <0.1 AU) while the others result in super-Earths at wider orbital radii. The volatile and ice abundance of relevant carbon and oxygen bearing molecular species are determined through a complex chemical kinetic code that includes both gas and grain surface chemistry. This is combined with a model for the abundance of the refractory dust grains to compute the total carbon and oxygen abundance in the protoplanetary disk available for incorporation into a planetary atmosphere. We include the effects of the refractory carbon depletion that has been observed in our solar system, and posit two models that would put this missing carbon back into the gas phase. This excess gaseous carbon then becomes important in determining the final planetary C/O because the gas disk now becomes more carbon rich relative to oxygen (high gaseous C/O). One model, where the carbon excess is maintained throughout the lifetime of the disk results in hot Jupiters that have super-stellar C/O. The other model deposits the excess carbon early in the disk life and allows it to advect with the bulk gas. In this model the excess carbon disappears into the host star within 0.8 Myr, returning the gas disk to its original (substellar) C/O, so the hot Jupiters all exclusively have substellar C/O. This shows that while the solids tend to be oxygen rich, hot Jupiters can have super-stellar C/O if a carbon excess can be maintained by some chemical processing of the dust grains. The atmospheric C/O of the super-Earths at larger radii are determined by the chemical interactions between the gas and ice phases of volatile species rather than the refractory carbon model. Whether the carbon and oxygen content of the atmosphere was accreted primarily by gas or solid accretion is heavily dependent on the mass of the atmosphere and where in the disk the growing planet accreted.

Super Earths are the largest population of exoplanets and are seen to exhibit a rich diversity of compositions as inferred through their mean densities. Here we present a model that combines equilibrium chemistry in evolving disks with core accretion that tracks materials accreted onto planets during their formation. In doing so, we aim to explain why super Earths form so frequently and how they acquire such a diverse range of compositions. A key feature of our model is disk inhomogeneities, or planet traps, that act as barriers to rapid type-I migration. The traps we include are the dead zone, which can be caused by either cosmic ray or X-ray ionization, the ice line, and the heat transition. We find that in disks with sufficiently long lifetimes ( 4 Myr), all traps produce Jovian planets. In these disks, planet formation in the heat transition and X-ray dead zone produces hot Jupiters while the ice line and cosmic ray dead zones produce Jupiters at roughly 1 AU. Super Earth formation takes place within short-lived disks ( 2 Myr), whereby the disks are photoevaporated while planets are in a slow phase of gas accretion. We find that super Earth compositions range from dry and rocky (< 6 % ice by mass) to those with substantial water contents (> 30 % ice by mass). The traps play a crucial role in our results, as they dictate where in the disk particular planets can accrete from, and what compositions they are able to acquire.