The environments forming stellar and planetary systems

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; Sébastien Maret; Nagayoshi Ohashi; Linda Podio; Víctor M. Rivilla; Giovanni Sabatini; Patricio Sanhueza; Dominique Segura-Cox; Kei Tanaka; Maxime Tanious; Fengwei Xu; Yao-Lun Yang; Qizhou Zhang

AI summary · arXiv: 2610.22462v1 · astro-ph.IM

The environments forming stellar and planetary systems

Michael Kuffmeier, Jaime E. Pineda, Peter Schilke, Jes K. Jørgensen, Korash Assani, Alain Baudry, Maite Beltrán, Eleonora Bianchi,

and 24 more authors

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, Sébastien Maret, Nagayoshi Ohashi, Linda Podio, Víctor M. Rivilla, Giovanni Sabatini, Patricio Sanhueza, Dominique Segura-Cox, Kei Tanaka, Maxime Tanious, Fengwei Xu, Yao-Lun Yang, Qizhou Zhang

Original paper Submitted to arXiv on 15 Oct. 2026 10 pages + 1 page affiliations, 1 figure, ALMA2040 whitepaper License: CC BY 4.0 Also in: fr

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The essentials

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.

Key points written by AI: they may contain errors, check them against the paper.

AI-generated keywords: Star formation Protoplanetary disks Environmental effects Accretion ALMA2040

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Original abstract

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.

Planets Begin Before the Disk: Why Stellar Birthplaces Matter

A planet’s story starts long before dust grains assemble into a world. It begins in the cloud where its parent star forms, amid gas flows, magnetic fields, radiation, and neighboring stars. Those surroundings help determine how much material reaches a young star’s disk, how that material moves, and which chemical ingredients it carries.

A scientific white paper for ALMA2040 argues that understanding these connections requires a broader view of planet formation. Instead of treating disks as isolated systems, astronomers need to follow material from its surrounding cloud into the disk—and then track what accretes onto the star or escapes in outflows.

The Limits of Studying Quiet Neighborhoods

Nearby, relatively isolated disks have provided much of the observational foundation for planet-formation models. They are accessible targets, but they may not represent the environments where most stars are born.

Most stars likely form in clusters. There, radiation from neighboring stars, close stellar encounters, and differences in pressure and ionization can influence disk assembly and evolution. These conditions may affect whether material produces planets, fragments into brown dwarfs, or helps build stellar companions.

Metallicity—the abundance of elements heavier than hydrogen and helium—adds another variable. It affects dust abundance, cooling, chemistry, and the supply of solids available to make planets. Comparisons across roughly 0.2 to 1 times solar metallicity could reveal whether these differences shape disks from the beginning, rather than only changing their later evolution.

Following the Supply Chain

The white paper does not report a new survey or simulation. Instead, it synthesizes existing observations and theory, identifies unresolved processes, and translates the measurements needed to investigate them into requirements for future telescope capabilities.

Its central strategy is to connect structures across vastly different scales: reservoirs extending approximately 1,000–5,000 astronomical units, narrow infalling streamers, disk-impact regions only a few astronomical units across, and the accretion flows and outflows that redistribute material. One astronomical unit, or au, is the average Earth–Sun distance.

Seeing Inflow Is Not the Same as Measuring Delivery

A streamer that appears to feed a disk does not automatically reveal how much mass it delivers. Estimates depend on assumed molecular abundances, excitation temperatures, and three-dimensional trajectories. Together, these uncertainties can change inferred accretion rates by as much as an order of magnitude.

Matched-resolution observations of faint molecular lines, dust emission, and polarization would help characterize density, temperature, motion, and magnetic-field structure. Observations at multiple epochs would add information about variability, helping astronomers distinguish a temporary snapshot from a sustained supply of material.

Does Incoming Material Keep Its Chemistry?

The chemical journey matters, too. Material may preserve ingredients inherited from its parent cloud, or undergo substantial transformation as it approaches and strikes a disk. Deuterated molecules, shock tracers, and complex organic species could help distinguish these possibilities. Such measurements would connect the chemistry of stellar birth environments to the inventory available for planet formation.

The Angular-Momentum Bottleneck

Incoming gas brings angular momentum, a measure of rotational motion. For material to move inward toward a star, some of that angular momentum must be transferred elsewhere. How this happens remains a major uncertainty.

Disk winds are a leading part of the picture, but current observations resolve them down to approximately 10 au in fewer than ten nearby systems. That makes their launching locations and mass-loading rates difficult to establish.

Resolution approaching 1 au would help separate wind streamlines and compare angular momentum entering through infall, remaining in the disk, and leaving through outflows. Any mismatch would constrain the additional roles required from magnetic stresses, gravitational structures, or companions. Longer-wavelength observations could also reveal disk mass hidden by optically thick emission, while rapid-response monitoring could help investigate triggers of accretion bursts.

What ALMA2040 Would Need

The paper’s principal quantitative outcomes are proposed capabilities—not demonstrated discoveries. Its priorities include:

Approximately tenfold improvements in both spectral-line and continuum sensitivity, enabling observations roughly 100 times faster at a fixed noise level.
Threefold longer baselines and angular resolution better than 5 milliarcseconds, probing sub-au scales nearby and approximately 10–25 au at distances of 2–5 kiloparsecs.
Velocity channels no wider than about 0.1 kilometres per second and brightness-temperature noise near 1 kelvin.
Instantaneous bandwidth of at least 128 gigahertz, ideally reaching 512 gigahertz through simultaneous multiband observations.

An ambitious 1-milliarcsecond goal would reach approximately 50 au in the Magellanic Clouds. That could distinguish massive protostellar disks there, but would still not resolve their inner planet-forming regions.

From Individual Disks to Environmental Tests

The potential payoff is a shift from studying a handful of systems to comparing hundreds across stellar masses and environments. But sharper images alone are insufficient: sensitivity must improve alongside resolution, and observations must recover extended emission rather than miss the surrounding reservoirs.

Chemical and dynamical models will remain essential for interpretation. Ultimately, the paper offers a roadmap for testing how a star’s birthplace shapes its emerging planetary system—and for moving beyond the assumption that our best-observed disks tell the whole story.

Created on 19 Oct. 2026

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The environments forming stellar and planetary systems

The essentials

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Definitions

Planets Begin Before the Disk: Why Stellar Birthplaces Matter

The Limits of Studying Quiet Neighborhoods

Following the Supply Chain

Seeing Inflow Is Not the Same as Measuring Delivery

Does Incoming Material Keep Its Chemistry?

The Angular-Momentum Bottleneck

What ALMA2040 Would Need

From Individual Disks to Environmental Tests

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