Joanna Drążkowska

Late infall can replenish the building materials of planets in protoplanetary disks and dramatically alter their structural evolution. The resulting pressure bumps effectively accumulate dust, facilitate grain coagulation, and trigger planetesimal formation via the streaming instability. In this work, we investigated the potential for planetesimal and planet formation, as well as the emergence of observable substructures, in disks undergoing late-stage infall. We utilized a comprehensive modeling framework that couples dust coagulation and dynamics, planetesimal formation, N -body gravity, planetary growth, and planet-disk interactions. Our results show that the abundant dust supply and the migration barrier created by the infalling gas enable the rapid formation of gas giants via pebble and gas accretion within one million years, even at large orbital distances (∼70 au). These giants, in turn, exert torques that generate multiple secondary disk substructures, fostering multigenerational planetesimal formation and resulting in diverse planetary system configurations. The planetesimals exhibit distinct dynamical properties that are determined by their formation epoch and environment, which are analogous to the small-body populations in the outer Solar System. Both the infall- and planet-induced substructures are clearly visible in synthetic 1.3-mm continuum observations, closely resembling the multi-ring disks detected in ALMA surveys. Our model provides a new perspective on the origin of distant giant planets, long-lasting planetesimal formation, and the prevalence of disks with multiple substructures.

Context . Nonideal magnetohydrodynamic (MHD) simulations of protoplanetary disks show a plethora of complex gas structures, including winds, rings, and gaps. These affect dust transport and help form dust traps, which are essential for planetesimal formation. Although studies have explored the evolution of dust in such systems, they have done so either in 1D or without dust coagulation, and the effect of such systems on dust growth is still an active area of research. Aims . We investigated the effect of a complex gas flow architecture on global dust evolution, including dust growth and transport. We examined the timescales of different processes impacting dust evolution and discuss prospects of forming planetesimals. Methods . We post-processed gas velocity output from a 2D nonideal MHD simulation using a 2D (r-z) Monte Carlo dust coagulation code to perform global simulations of dust growth and evolution. We performed three runs, one with a typical steady-state disk and two with the gas velocity from the MHD simulation, in which we varied the fragmentation velocity. Results . Our results show that the advection of small particles by the gas due to high gas velocities can play an important role in setting the dust size distributions around protoplanetary disks. The gas flow structure has a transition region, and this region acts as a location of dust pile-up, increasing the pebble-to-gas ratio by a factor of 2.5 when compared to the steady-state disk. Lowering the fragmentation velocity improves the stability of the pile-up, but the pebble concentration is not as high. In this scenario, a dust trap can be formed in a disk without the need for a pressure bump. We discuss the possibilities for planetesimal formation in such a trap.

The volatile composition of icy bodies provides important clues to the chemical inheritance linking molecular clouds, protoplanetary disks, and forming planetary systems. While water ice is generally expected to dominate the volatile inventory of bodies formed in the outer Solar System, observations of comets and trans-Neptunian objects reveal substantial diversity in ice abundances, including unexpectedly high CO-to-water ratios in some objects. Understanding how such CO-rich reservoirs form and evolve is therefore essential for connecting disk ice chemistry with the volatile composition of planetesimals and planets.In this contribution, I present results of a recent study (Drazkowska 2026) using a one-dimensional disk model including dust coagulation, fragmentation, radial drift, volatile evaporation and recondensation, and planetesimal formation via the streaming instability. In particular, I explore how the disk buildup stage influences the chemical evolution of icy solids and the preservation of volatile-rich reservoirs.CO-rich pebbles naturally form near the CO snow line due to the cold-finger effect, where outward-diffusing CO vapor recondenses onto drifting grains. This process efficiently enhances the CO ice abundance in solids and occurs regardless of whether disk buildup is included. However, models incorporating the buildup phase produce significantly stronger CO enrichment relative to water in the outer disk, demonstrating that early disk evolution can substantially modify the volatile composition inherited by icy solids. Despite the formation of CO-rich pebbles, smooth disk models do not produce CO-rich planetesimals. This suggests that additional mechanisms are required to retain or trap CO-rich solids.These results highlight the importance of volatile transport and ice reprocessing in regulating the chemical inheritance of forming planetary systems. In particular, models aiming to connect disk chemistry with cometary compositions and exoplanet atmospheric C/O ratios should account for the disk buildup stage, which can significantly alter the spatial distribution and incorporation of volatile species into solids.

The water snowline is thought to play a key role in the formation of the first planetesimals. Planetesimal formation requires efficient local concentration of large pebbles, a condition that is difficult to achieve throughout protoplanetary disks. Near the snowline, icy grains are expected to stick more efficiently than silicate grains as they approach their sublimation temperature. In addition, water vapor from the hotter inner disk can diffuse outward, recondense onto solids in colder regions, and thereby enhance the local solid-to-gas ratio. Together, these processes make the snowline a particularly favorable site for planetesimal formation. Whether iron meteorites, which likely formed within the first Myr of the solar system formation, originated near the snowline remains an open question [1-3].While planetesimal formation at the water snowline has been extensively studied, most previous models assume a single dust size and composition at each radial location and neglect the vertical structure of the disk. In reality, dust particles grow and fragment into a distribution of sizes that evolve differently in both the radial and vertical directions, an aspect that has been shown to impact late-stage planetesimal formation beyond the water snowline, in regions linked to the formation of chondritic meteorites [4]. Small grains are also known to acquire proportionally more water ice than larger grains, potentially affecting the water enrichment near the snowline [5].In this talk, we present a new Monte Carlo model to investigate the coupled evolution of dust composed of ice and silicate in young two-dimensional disks [6]. Our model includes dust coagulation and fragmentation, ice evaporation and condensation on grains of different sizes, and the radial and vertical transport of both solids and water vapor. This approach enables us to constrain the ice-to-rock ratios of planetesimals forming at the water snowline and to trace the evolutionary history of water ice before its incorporation into planetesimals. The predicted composition and formation timescales of these planetesimals will be compared to those observed among meteorites, and thus could eventually constrain whether some iron meteorite parent bodies formed near the water snowline. References:[1] J. Drazkowska and Y. Alibert, 2017, Astronomy & Astrophysics, 608, A92[2] T. Lichtenberg, J. Drazkowska, M. Schönbächler, et al., 2021, Science, 371, 6527[3] A. Morbidelli, K. Baillié, K. Batygin, et al., 2022, Nature Astronomy, 6, pages 72–79[4] N. Gurrutxaga, J. Drazkowska, V. Vaikundaraman, T. Kleine, 2026, The Astrophysical Journal, in press[5] S. Krijt, F. Ciesla, A. Bergin, 2016, The Astrophysical Journal, 833, 2[6] N. Gurrutxaga, V. Vaikundaraman, J. Drazkowska, 2026, Astronomy & Astrophysics, 709, A164

The scarcity of giant planets around M dwarfs raises important questions about the physical processes that regulate planet formation around the least massive stars. In this work, we investigate planet formation around very low-mass stars using N-body simulations that incorporate pebble accretion, gas accretion, planet-disk interactions, star-planet tidal interactions, and stellar evolution during the pre-main-sequence phase. We explore how disk properties influence planetary growth and migration by assuming a compact dust disk of 30 au.Our simulations show that low-viscosity disks naturally favor the formation of close-in super-Earths, while the scarcity of larger planets around M dwarfs emerges as a natural outcome of the planet formation process. In cases where planet-planet collisions efficiently assemble cores of 2–3 Earth masses, close-in mini-Neptunes and Neptune-mass planets may form. Moreover, if planetary cores reach masses of ~5 Earth masses within the first ~1 Myr, cold giant planets with masses between Saturn and Jupiter can form at distances of 1–5 au, provided that the disks are massive (~10% of the stellar mass), weakly turbulent (αt = 10-4), and long-lived (10 Myr).We further investigate the role of fragmentation in the formation of planetary cores by introducing an evolving pebble flux linked to different fragmentation velocities associated with distinct grain compositions across the disk. These results provide new insights into the diversity of planetary systems around M dwarfs and the conditions required for giant planet formation in the low-stellar-mass regime.

Carbonaceous chondrites are samples from planetesimals that formed 2–4 million years after solar system formation began. They consist of distinct dust components formed at different times and locations in the accretion disk, and whose abundances in carbonaceous chondrites vary over planetesimal formation time. The mechanism that led to this time-varied accretion is not understood, but it is critical for understanding late-stage planetesimal formation. Using a two-dimensional Monte Carlo simulation of dust evolution, we show that differences in dust filtering and delivery rates of distinct dust components to a planet-induced pressure bump in the disk reproduce the observed compositions and formation ages of the carbonaceous chondrites. This implies that carbonaceous chondrites likely formed in a single, long-lived dust trap, most likely outside of Jupiter’s orbit. Because differentiated meteorites, which sample an earlier generation of planetesimals, exhibit similar isotopic variability as the chondrites, they likely have also formed in dust traps, implying these structures were the dominant site for planetesimal formation in the solar system.

Dust growth is a crucial step in planet formation, and the efficiency of this process is controlled by the physical and chemical properties of the dust grains. Monte Carlo–based methods are commonly used to follow the collisional evolution of dust while tracking their properties. However, current Monte Carlo methods in planet formation do not strictly conserve the global inventory of dust properties across the protoplanetary disk, causing fluctuations that can grow over time and affect predictions of dust evolution. Here we present a coagulation algorithm that ensures the global conservation of dust properties while resolving the spatial evolution of dust. The method is validated against analytical solutions for standard coagulation kernels and benchmarked in a two-dimensional disk. We show that the method reproduces standard results, resolves the full dust population, and improves the resolution of the small-grain regime compared to other Monte Carlo methods for modeling global dust evolution. Finally, using a test case that includes sublimation and condensation of water interacting with silicates, we demonstrate strict conservation of each component’s mass during coagulation, establishing the method as a valuable tool for tracking dust properties in protoplanetary disks.