# The environments forming stellar and planetary systems **Authors:** Michael Kuffmeier, Jaime E. Pineda, Peter Schilke, Jes K. Jørgensen, Korash Assani, Alain Baudry, Maite Beltrán, Eleonora Bianchi, Claudio Codella, Laura Colzi, Audrey Coutens, Timea Csengeri, Maria Drozdovskaya, Vardan Elbakyan, Francesco Fontani, Gary Fuller, Josep Miquel Girart, Katharine Johnston, Pamela Klaassen, Rolf Kuiper **arXiv:** [2610.22462](https://arxiv.org/abs/2610.22462) **Date:** 2026-10-15 **Summary page:** https://www.summarizepaper.com/en/arxiv-id/2610.22462v1/ ## Key points - Purpose: The ALMA2040 white paper examines how stellar birth environments shape the mass, angular momentum, and chemistry of disks, influencing planets, brown dwarfs, and stellar companions. - Environmental diversity: Isolated, solar-metallicity disks are an incomplete basis for planet-formation models; clustered environments and varying metallicity alter radiation, dynamics, cooling, chemistry, and available solids. - Evidence base: The paper synthesizes existing observations and theory and proposes future telescope capabilities; it does not present a new survey, simulation, or demonstrated discoveries. - Observational strategy: Trace material from molecular clouds through infalling streamers into disks, accretion flows, and outflows using matched-resolution molecular-line, continuum, polarization, and multi-epoch observations. - Mass delivery: Apparent inflow does not establish how much mass reaches a disk; streamer accretion estimates have uncertainties of up to an order of magnitude. - Chemistry: Connecting reservoirs roughly 1,000–5,000 au across to disk-impact regions a few au across could reveal whether incoming material preserves or transforms its chemical inventory. - Angular momentum: Approximately 1 au resolution would help measure wind launching and compare angular momentum entering disks, remaining within them, and escaping through outflows. - Proposed upgrades: ALMA2040 requires approximately tenfold improvements in spectral-line and continuum sensitivity and threefold longer baselines, potentially enabling observations 100 times faster and samples of hundreds of objects. - Technical requirements: Targets include resolution better than 5 milliarcseconds, velocity channels no wider than about 0.1 km/s, brightness-temperature noise near 1 K, and instantaneous bandwidth of at least 128 GHz, ideally 512 GHz. - Reach and limits: A more ambitious 1-milliarcsecond resolution would probe approximately 50 au in the Magellanic Clouds, distinguishing massive protostellar disks but not their inner planet-forming regions. - Conclusion: Sensitivity and resolution must improve together; comparisons across approximately 0.2–1 times solar metallicity also require extended-emission recovery and chemical and dynamical modeling. ## Summary This scientific white paper for ALMA2040 examines how a star’s birth environment determines the mass, angular momentum, and chemical inventory delivered to its planet-forming disk, and how these conditions influence the formation of planets, brown dwarfs, and stellar companions. The authors argue that nearby, relatively isolated disks with solar metallicity provide an incomplete foundation for planet-formation models. Most stars likely form in clusters, where radiation, stellar encounters, pressure, and ionization can differ substantially from conditions in isolated regions. Metallicity adds further variation by affecting dust abundance, cooling, chemistry, and the supply of solid material available for planet formation. Rather than presenting a new observational survey or simulation, the paper synthesizes existing observations and theoretical research, identifies unresolved physical processes, and translates the measurements needed to investigate them into telescope requirements. Its proposed strategy traces material from molecular-cloud structures through infalling streamers into disks, and subsequently through accretion and outflows. Matched-resolution observations of faint molecular lines, dust continuum emission, and polarization, combined with observations at multiple epochs, would characterize density, temperature, velocity, chemical composition, and variability across stellar masses and environments. A central challenge is that detecting an apparent inflow does not establish how much mass it delivers. Existing estimates of streamer accretion rates depend on assumed molecular abundances, excitation temperatures, and three-dimensional trajectories, resulting in uncertainties of up to an order of magnitude. The authors propose linking reservoirs extending roughly 1,000–5,000 astronomical units (au) to disk-impact regions only a few au across. Chemical diagnostics, including deuterated molecules, shock tracers, and complex organic species, could reveal whether incoming material retains its inherited composition or undergoes chemical transformation during accretion. Angular-momentum removal remains another major uncertainty. Current observations resolve disk winds down to approximately 10 au in fewer than ten nearby systems, making wind-launching radii and mass-loading rates difficult to determine. Resolution of approximately 1 au would help distinguish wind streamlines and compare the angular momentum entering through infall, remaining in the disk, and escaping through outflows. Any imbalance would constrain the contributions required from magnetic stresses, gravitational structures, or companions. Longer-wavelength observations would also probe disk mass obscured by optical depth, while rapid-response monitoring could help distinguish possible triggers of accretion bursts. The paper’s principal quantitative outcomes are proposed capabilities, not demonstrated results. ALMA2040 would require approximately tenfold improvements in both spectral-line and continuum sensitivity relative to current ALMA capabilities, together with threefold longer baselines. The sensitivity improvement would enable observations roughly 100 times faster at a fixed noise level, potentially expanding samples from a handful of objects to hundreds. Angular resolution better than 5 milliarcseconds would probe sub-au scales in nearby systems and approximately 10–25 au at distances of 2–5 kiloparsecs. A more ambitious goal of 1 milliarcsecond would reach approximately 50 au in the Magellanic Clouds. Additional requirements include velocity channels no wider than about 0.1 kilometres per second, brightness-temperature noise near 1 kelvin, and instantaneous bandwidth of at least 128 gigahertz, ideally reaching 512 gigahertz through simultaneous multiband observations. The authors conclude that sensitivity and resolution must improve together to connect environmental conditions with disk evolution, fragmentation, and emerging system architectures. Comparisons spanning approximately 0.2–1 times solar metallicity would test whether environmental differences affect disk assembly as well as subsequent evolution. However, the proposed discoveries depend on future instrumentation, adequate recovery of extended emission, and interpretation informed by chemical and dynamical models. Even the most ambitious resolution would distinguish massive protostellar disks in the Magellanic Clouds without resolving their inner planet-forming regions.