Early planetary formation processes during the assembling of the protoplantary disk – DISKBUILD

The DISKBUILD project relied on a multi-scale, interdisciplinary methodology combining high-resolution numerical simulations and physico-chemical modeling. The dynamical evolution of collapsing molecular cloud cores and the formation of protostar–disk systems were simulated using the RAMSES code, solving the full set of radiative magneto-hydrodynamical (RMHD) equations with self-gravity and magnetic fields. Particular attention was given to spatial resolution in order to resolve sub-AU scales and to minimize the use of simplified sink prescriptions. The simulations provided detailed information on density, temperature, velocity fields, and accretion flows within the young disk. These outputs were used to constrain dust transport processes, including radial and vertical motions. In parallel, a new time-dependent kinetic condensation model (KineCond) was developed to compute non-equilibrium gas–solid reactions under varying pressure and cooling timescales. The model explicitly accounts for condensation and evaporation kinetics and allows exploration of a wide thermodynamic parameter space. By combining dynamical simulations and kinetic chemistry, DISKBUILD established a coherent framework linking disk assembly and the formation of the first Solar System solids.

The DISKBUILD project achieved major advances through state-of-the-art radiative magneto-hydrodynamical (RMHD) simulations of molecular cloud collapse. These simulations followed the full sequence from prestellar core contraction to protostar formation and disk assembly, resolving spatial scales down to the sub-AU regime. By explicitly modeling gravity, magnetic fields, and radiative transfer, the calculations captured the formation of the first and second cores and the emergence of the circumstellar disk without relying solely on simplified prescriptions. The results show that disk formation is a natural outcome of magnetized collapse and that the internal disk structure—surface density, temperature gradients, and stability properties—converges toward robust profiles. The simulations also revealed anisotropic accretion streams and transient meridional circulation patterns that can efficiently redistribute angular momentum and transport dust. These findings demonstrate that early disks are dynamically structured environments shaped by ongoing infall rather than static systems. The RMHD framework developed in DISKBUILD provides quantitative constraints on accretion rates, thermal conditions, and disk morphology during the first 10⁴–10⁵ years. This dynamical foundation was then used to interpret the thermal histories relevant for solid formation and to connect collapse physics with the chemical evolution of the young Solar System.

The DISKBUILD project achieved its main scientific objectives and produced significant advances in the understanding of protoplanetary disk formation and early Solar System evolution. A major component of the project consisted of high-resolution radiative magneto-hydrodynamical (RMHD) simulations of molecular cloud collapse leading to the formation of protostars and circumstellar disks. These simulations (Ahmad et al. 2023, 2024, 2025) followed the evolution from prestellar core collapse to the birth of a protostar and its disk at sub-AU scales. The results show that disk formation is a natural outcome of magnetized collapse and that young disks develop robust density and temperature structures that are only weakly dependent on the initial conditions of the parent cloud. The simulations also revealed anisotropic accretion flows and transient meridional circulation patterns capable of redistributing angular momentum and transporting dust grains within the disk.

A second set of results concerns the dynamics and evolution of dust in star-forming environments. Simulations of dust dynamics in turbulent molecular clouds (Commerçon et al. 2023) identified the conditions under which dust grains decouple from the gas and develop independent dynamics. Additional studies explored dust processing during protostellar collapse (Borderies et al. 2025) and the dynamical properties of young disks, including the possibility that disks may be born eccentric (Commerçon et al. 2024). These processes provide a dynamical framework for understanding the transport of high-temperature materials toward the outer disk, consistent with cosmochemical constraints (Bhandare et al. 2024). Other work examined the large-scale structure of protoplanetary disks and proposed that an early inflationary phase may explain the presence of extended dust disks (Marschall & Morbidelli 2023).

Finally, the project investigated the chemical conditions of solid formation in protoplanetary disks. A new time-dependent kinetic condensation model (KineCond) was developed to explore non-equilibrium condensation processes. This work culminated in a recent article accepted in Nature (Charnoz et al. 2026), showing that non-equilibrium condensation naturally produces three mineralogical regimes corresponding to the main classes of chondritic meteorites. Together, these results establish a coherent framework linking disk assembly, dust dynamics, and the formation conditions of the first Solar System solids.

Planets form in a protoplanetary disks (PPD) around a protostar. There are growing evidences from meteoritic records inside the Solar System, and observational evidence from ALMA observations that planet accretion processes started during the cloud infall during 100Kyrs to, possibly a few Myr. However most planet formation studies assume accretion in an isolated disk. Meteoritic records of Solar System material find growing evidence for injection of interstellar material in the Solar Nebula, as well as separations of isotopic anomalies reservoir that cannot be explained with the classical paradigm of an isolated disk. Our aim is to investigate the material inflow onto an assembling PPD and how this modifies the dust transport, planetesimal formation and planet migration using a combination of state-of-the-art 3D MHD multi-scale models, 1D dust growth, planetesimals formation and transport models and models of planet migration. The DISKBUILD project gathers 3 teams from different communities (star formation, planet formation, cosmochemistry) to investigate s (1) the structure of the gas/dust flux on the newly formed disk (2) its thermal structure (3) the injection and diffusion of dust in the disk (4) how dust and gas is transported and when and where planetesimals form and (5) how planets migrate in a non isolated disk. This will provide a new framework for planet formation and our results will be confronted to meteoritic records in priority and also to observations of young disk in planet forming regions. It will bridge the gap between planets and the interstellar medium to offer new perspective to interpret meteoritic data and to understand how the first solids of the Solar System form.