Constraining ionization and excitation processes in protoplanetary disks is essential for understanding the chemical structure and evolution of disk material, shaping planet formation pathways. We present JWST/NIRSpec IFU observations of the edge-on disk Oph 163131, which reveal a unusual ro-vibrational H_2 spectrum dominated by the 1–0 O(2) line (2.627 μm), with suppressed higher-J emission despite excitation to v=2 and 3. This vibrationally hot, rotationally cold H_2 emission is spatially extended, broadly following the molecular disk traced by CO(J=2–1), with emission increasing above and below a thin midplane dark lane and extending radially beyond ∼200 au, where near-IR scattered-light emission is no longer dominant. We interpret the observed H_2 emission as arising from non-thermal excitation in cold, dense outer-disk gas, where collisions depopulate higher-J rotational levels within each vibrational manifold prior to emission, producing the characteristic “v-hot, J-cold" spectrum. We consider both ultraviolet irradiation and cosmic-ray excitation as contributors to the H_2 emission and find that their combined action, together with collisional de-excitation of high-J level populations, broadly reproduces the observed line ratios and morphology. Within this framework, we infer a rather high effective cosmic-ray ionization rate of ∼(1-10)×10^-15 s^-1 in the presence of a moderate UV field (χ_UV=100-1000, in Draine units). These results for disks, together with the recent findings by Bialy et al. 2025 for the lower-density starless core B68, highlight the potential of ro-vibrational H_2 emission as a novel probe of cosmic-ray ionization.

Constraining ionization and excitation processes in protoplanetary disks is essential for understanding the chemical structure and evolution of disk material, shaping planet formation pathways. We present JWST/NIRSpec integral-field-unit observations of the edge-on disk Oph 163131, which reveal an unusual rovibrational H _2 spectrum dominated by the 1–0 O(2) line (2.627 μ m), with suppressed higher- J emission despite excitation to v = 2 and 3. This vibrationally hot, rotationally cold H _2 emission is spatially extended, broadly following the molecular disk traced by CO( J = 2–1), with emission increasing above and below a thin midplane dark lane and extending radially beyond ∼200 au, where near-IR scattered-light emission is no longer dominant. We interpret the observed H _2 emission as arising from nonthermal excitation in cold, dense outer-disk gas, where collisions depopulate higher- J rotational levels within each vibrational manifold prior to emission, producing the characteristic “ v -hot, J -cold” spectrum. We consider both ultraviolet irradiation and cosmic-ray excitation as contributors to the H _2 emission and find that their combined action, together with collisional deexcitation of high- J level populations, broadly reproduces the observed line ratios and morphology. Within this framework, we infer a rather high effective cosmic-ray ionization rate of ∼(1–10) × 10 ^−15 s ^−1 in the presence of a moderate UV field ( χ _UV = 100−1000, in Draine units). These results for disks, together with the recent findings by Bialy et al. for the lower-density starless core B68, highlight the potential of ro-vibrational H _2 emission as a novel probe of cosmic-ray ionization.

We present deep, high-resolution (similar to 100 mas) Karl G. Jansky Very Large Array Ka-band (9.1 mm) observations of the disk around MWC 480 and infer dust properties through a combined analysis with archival Atacama Large Millimeter/submillimeter Array data at 0.87, 1.17, 1.33, and 3.0 mm. The prominent dust ring at 95 au (B95) is detected at 9.1 mm for the first time, while the faint outer ring at 160 au is not revealed. Through nonparametric visibility modeling, we identified two new annular features: a plateau within 20-50 au across all wavelengths, and a shoulder exterior to the B95 ring at 0.87, 1.17, and 1.33 mm, consistent with signatures of planet-disk interaction. We find that the width of the B95 ring remains constant across wavelengths, suggesting that fragmentation dominates over radial diffusion or that unresolved substructure is present within the ring. Resolved spectral modeling yields two families of dust solutions that reproduce the observations equally well: compact grains or highly porous (90%) grains, with carbonaceous components dominated by refractory organics or amorphous carbon, respectively. The inferred maximum grain sizes peak at the locations of the two rings and reach centimeter within the B95 ring. The total dust masses are 860-78+95M circle plus / 1500-330+440M circle plus (large/small-grain solution in inner disk) and 230-13+14M circle plus for the two dust mixtures. The B95 ring alone contains 100-5+5M circle plus and 43-2+2M circle plus , respectively, sufficient to assemble the cores of giant planets. Finally, we highlight the power of broadband, multiwavelength observations in placing better constraints on dust composition and porosity in protoplanetary disks.

Context. Protostellar winds can theoretically lift solids from the planet-forming disks, but direct evidence for launched dust has been scarce so far. Numerous atomic lines that are unique to mid-infrared (IR) wavelengths reveal refractories eroded from dust grains and provide information on wind properties in the earliest stages of the star formation process.Aims. We characterize the gas-phase composition, shock properties, and dust content of the jet from the Class 0 protostar BHR71-IRS1, one of the best cases of a resolved central jet inside a wide-angle wind.Methods. We present JWST MIRI-MRS spectral imaging of the inner 2000 au of the BHR71-IRS1 blueshifted side of the outflow. Atomic line intensities were compared to shock models to constrain the physical conditions and elemental abundances of the outflowing gas. Dust continuum maps were constructed from point spread function-subtracted cubes, and the spectral energy distribution of the dust was analyzed.Results. The ionized central jet of BHR71-IRS1 is spatially resolved and imaged for the first time, revealing a unique inventory of refractory, volatile, and noble-gas fine-structure lines (Fe, Ni, Co, Cl, S, Ne, and Ar). The emission is concentrated along four bright knots that wiggle along the jet axis. Point spread function-subtracted continuum maps reveal extended mid-IR continuum emission cospatial with the jet bullets and within the H2-traced outflow cone. Spectral energy distributions along the jet were fit together with the extinction, revealing a warm (200-400 K) and a cold (70-90 K) dust component. The shock modeling constrained by the mid-IR lines indicates a decline in the shock velocity from 70 to 35 km s(-1) and in the pre-shock density from >105 to 4 & times; 10(4) cm(-3) with distance from the protostar. Gas-phase Fe and Ni are measurably depleted relative to solar abundances. This is consistent with a substantial fraction of refractories remaining locked in grains in spite of the shocks.Conclusions. These JWST observations provide direct evidence that dust is launched in a Class 0 jet and at least partly survives shock processing. The richness of refractory tracers in the BHR71-IRS1 jet provides a window into the inner-disk composition at the onset of planet formation.

This document contains the supplementary materials (Appendix B, C, and D) of the paper 'Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS). V. Tracing cavity walls and shocked knots with non-thermally desorbed CH3OH in BHR71-IRS1'.

Context. Protostellar winds can theoretically lift solids from the planet-forming disks, but direct evidence for launched dust has been scarce so far. Numerous atomic lines that are unique to mid-infrared (IR) wavelengths reveal refractories eroded from dust grains and provide information on wind properties in the earliest stages of the star formation process. Aims. We characterize the gas-phase composition, shock properties, and dust content of the jet from the Class 0 protostar BHR71-IRS1, one of the best cases of a resolved central jet inside a wide-angle wind. Methods. We present JWST MIRI-MRS spectral imaging of the inner 2000 au of the BHR71-IRS1 blueshifted side of the outflow. Atomic line intensities were compared to shock models to constrain the physical conditions and elemental abundances of the outflowing gas. Dust continuum maps were constructed from point spread function-subtracted cubes, and the spectral energy distribution of the dust was analyzed. Results. The ionized central jet of BHR71-IRS1 is spatially resolved and imaged for the first time, revealing a unique inventory of refractory, volatile, and noble-gas fine-structure lines (Fe, Ni, Co, Cl, S, Ne, and Ar). The emission is concentrated along four bright knots that wiggle along the jet axis. Point spread function-subtracted continuum maps reveal extended mid-IR continuum emission cospatial with the jet bullets and within the H2-traced outflow cone. Spectral energy distributions along the jet were fit together with the extinction, revealing a warm (200-400 K) and a cold (70-90 K) dust component. The shock modeling constrained by the mid-IR lines indicates a decline in the shock velocity from 70 to 35 km s−1 and in the pre-shock density from >105 to 4 × 104 cm−3 with distance from the protostar. Gas-phase Fe and Ni are measurably depleted relative to solar abundances. This is consistent with a substantial fraction of refractories remaining locked in grains in spite of the shocks. Conclusions. These JWST observations provide direct evidence that dust is launched in a Class 0 jet and at least partly survives shock processing. The richness of refractory tracers in the BHR71-IRS1 jet provides a window into the inner-disk composition at the onset of planet formation.

Aims. Edge-on discs offer a unique opportunity to probe radial and vertical dust and gas distributions in the protoplanetary phase. This study aims to investigate the distribution of micron-sized dust particles in the Flying Saucer in Rho Ophiuchi by leveraging the unique observational conditions of a bright infrared background that enables the edge-on disc to be seen in both silhouette and scattered light at specific wavelengths. Methods. We used NIRSpec IFU observations from the JWST Edge-on Disc Ice program (JEDIce) of the Flying Saucer serendipitously observed against a Polycyclic Aromatic Hydrocarbons-emitting background to constrain the dust distribution and grain sizes via radiative transfer modelling. Results. The observation of the Flying Saucer in silhouette at 3.29 μm reveals that the midplane radial extent of small dust grains is ∼235 au, i.e. larger than the large-grain disc extent previously determined to be 190 au from millimetre data. The scattered light observed in emission probes micron-sized icy grains at large vertical distances above the midplane. The vertical extent of the disc silhouette is similar at visible, near-IR, and mid-IR wavelengths, corroborating the conclusion that dust settling is inefficient for grains as large as tens of microns, both vertically and radially.

The icy material within protoplanetary disks plays a central role in planet formation, yet remains poorly characterized by observations. We present 1.6-28 mu m spectra of five disks obtained as part of the JWST Edge-on Disk Ice program, representing the largest survey of disk ices to date. The major ice species H2O, CO2, and CO are detected toward all disks, and exhibit a wide range of absolute optical depths and optical depth ratios across the sample. This is suggestive of a range of ice abundances and compositions, but quantitative constraints will require radiative transfer modeling. All disks exhibit ice features across the entire spatial region where the IR continuum is detected; vertically elevated ice grains therefore seem to be ubiquitous in disks. The CO ice is consistently dominated by apolar CO:CO2 mixtures, implying that the disk ice compositions are neither completely reset nor pristinely inherited from the protostellar stage. The presence of these mixtures also suggests that entrapment may be important in shaping the spatial distribution of CO within the disks. Small molecules commonly seen in protostellar ices (CH4, CH3OH, and NH3) are generally not detected in our sample, though tracers of ammonium salts (OCN- and the 6.85 mu m band) are common, potentially reflecting an evolution toward comet-like ice compositions. The spectra also contain a wealth of information about the micron-sized dust, atomic and molecular gas, and polycyclic aromatic hydrocarbon content, which together with the ice constraints will provide a comprehensive picture of the chemical, physical, and dynamical state of these systems.

Infrared Dark Clouds are ideal sites for investigating the initial conditions of massive star and cluster formation. The A Lei Of the Habitat and Assembly of Infrared Dark Clouds (ALOHA IRDCs), a James Clerk Maxwell Telescope (JCMT) Large Program, has mapped nearby IRDCs with SCUBA-2. Complementary molecular line observations are needed to characterise the physical, kinematic, and chemical properties of the dense gas. We aim to determine the thermal, kinematic, and chemical properties of clumps identified in the ALOHA IRDCs, and to assess their evolutionary status and level of star-forming activity. We performed single-pointing K-band and W-band observations towards 56 ALOHA IRDCs clumps using the Effelsberg 100-m and Yebes 40-m telescopes, respectively. We derived NH3 kinetic temperatures using the hyperfine group ratio (HFGR) method and identified infall and shock signatures from HCO+, H13CO+, SiO, and HNCO profiles. Water masers and NH2D emission were used as complementary tracers of chemical evolution and star formation. The clumps exhibit kinetic temperatures of 15-29 K. We detect NH2D emission towards 18 sources, with NH2D centroid velocities consistent with NH3, indicating both species trace the same dense gas component. More than half of the clumps display blue-asymmetric HCO+ profiles, identifying them as infall candidates. Water masers are detected in 22 sources, with prominent velocity ranges and variability. Broad SiO emission (> 20 km/s) indicates strong shocks, while narrower extents (< 6km/s) likely trace large-scale interactions or low-velocity shocks. The widespread infall signatures, shock tracers, masers, and NH2D emission suggest that relatively quiescent, chemically young material can coexist with dynamically active gas affected by early protostellar feedback, providing insight into the coupled physical and chemical evolution of massive IRDC clumps.

Planet formation starts in disks that are still embedded within their natal envelopes. Here, we compile an extensive inventory of the chemical composition of the disk and envelope ($<$ 3500 au) around the Class 0 protostar L1527 IRS. Using all publicly available ALMA (Atacama Large Millimeter/submillimeter Array) data, we report the detection of 39 molecules, including isotopologues. Of these, 22 are different molecular species and 28 are reported here for the first time toward L1527 in ALMA observations. CH$_3$OH is the only complex organic molecule detected, while the hydrocarbon CH$_3$CCH is the largest molecule detected. Overall, only a few programs are sensitive enough to detect emission unambiguously originating from the disk based on the kinematics. Nitrogen-bearing molecules are predominantly detected on more extended scales, while hydrocarbons show a distinct tail roughly along the southeastern outflow cavity wall, probably due to a stronger UV field in the eastern outflow lobe. The L1527 IRS protostellar system is not rich in sulfur-bearing molecules, with only strong emission observed for CS and SO. Overall, the envelope appears dominated by a carbon-rich chemistry, which seems to transition into an oxygen-rich chemistry in the disk. We calculate column densities of all detected species, providing a starting point to quantify the chemical diversity among young disks and the chemical evolution of the planet-forming material.

We present a JWST MIRI/MRS spectrum of the inner disk of WISE J044634.16–262756.1B (hereafter J0446B), an old (∼34 Myr) M4.5 star but with hints of ongoing accretion. The spectrum is molecule-rich and dominated by hydrocarbons. We detect 14 molecular species (H 2 , CH 3 , CH 4 , C 2 H 2 , 13 CCH 2 , C 2 H 4 , C 2 H 6 , C 3 H 4 , C 4 H 2 , C 6 H 6 , HCN, HC 3 N, CO 2 , and 13 CO 2 ) and two atomic lines ([Ne ii ] and [Ar ii ]), all observed for the first time in a disk at this age. The detection of spatially unresolved H 2 and Ne gas strongly supports that J0446B hosts a long-lived primordial disk, rather than a debris disk. The marginal H 2 O detection and the high C 2 H 2 /CO 2 column density ratio indicate that the inner disk of J0446B has a very carbon-rich chemistry, with a gas-phase C/O ratio ≳2, consistent with what has been found in most primordial disks around similarly low-mass stars. In the absence of significant outer disk dust substructures, inner disks are expected to first become water-rich due to the rapid inward drift of icy pebbles and evolve into carbon-rich as outer disk gas flows inward on longer timescales. The faint millimeter emission in such low-mass star disks implies that they may have depleted their outer icy pebble reservoir early and already passed the water-rich phase. Models with pebble drift and volatile transport suggest that maintaining a carbon-rich chemistry for tens of Myr likely requires a slowly evolving disk with α -viscosity ≲10 −4 . This study represents the first detailed characterization of disk gas at ∼30 Myr, strongly motivating further studies into the final stages of disk evolution.

Terrestrial planets and small bodies in our Solar System are theorized to have assembled from interstellar solids mixed with rocky solids that precipitated from a hot, cooling gas1,2. The first high-temperature minerals to recondense from this gaseous reservoir start the clock on planet formation3,4. However, the production mechanism of this initial hot gas and its importance to planet formation in other systems are unclear. Here we report the astronomical detection of this t = 0 moment, capturing the building blocks of a new planetary system beginning its assembly. The young protostar HOPS-315 is observed at infrared and millimetre wavelengths with the James Webb Space Telescope (JWST) and the Atacama Large Millimeter Array (ALMA), revealing a reservoir of warm silicon monoxide gas and crystalline silicate minerals low in the atmosphere of a disk within 2.2 AU of the star, physically isolated from the millimetre SiO jet. Comparison with condensation models with rapid grain growth and disk structure models suggests the formation of refractory solids analogous to those in our Solar System. Our results indicate that the environment in the inner disk region is influenced by sublimation of interstellar solids and subsequent refractory solid recondensation from this gas reservoir on timescales comparable with refractory condensation in our own Solar System.

Context. Protostars contain icy ingredients necessary for the formation of potential habitable worlds, therefore, it is crucial to understand their chemical and physical environments. This work is focused on the ice features towards the binary protostellar system Ced 110 IRS4A and IRS4B, separated by 250 au and observed with James Webb Space Telescope (JWST) as part of the Early Release Science (ERS) Ice Age collaboration. Aims. This study is aimed at exploring the JWST observations of the binary protostellar system Ced 110 IRS4A and IRS4B primarily to unveil and quantify the ice inventories towards these sources. Finally, we compare the ice abundances with those found for the same molecular cloud. Methods. We used data from multiple JWST instruments (NIRSpec, NIRCam, and MIRI) to identify and quantify ice species in the Ced 110 IRS4 system. The analysis was performed by fitting or comparing the laboratory infrared spectra of ices to the observations. Spectral fits are carried out with the ENIIGMA fitting tool that searches for the best fit out of a large number of solutions. The degeneracies of the fits are also addressed and the ice column densities are calculated. In cases where the full nature of the absorption features is not yet known, we explore different laboratory ice spectra to compare them with the observations. Results. We provide a list of securely and tentatively detected ice species towards the primary and the companion sources. For Ced 110 IRS4B, we detected the major ice species H2O, CO, CO2, and NH3. All species are found in a mixture except for CO and CO2, which have both mixed and pure ice components. In the case of Ced 110 IRS4A, we detected the same major species as in Ced 110 IRS4B, as well as the following minor species: CH4, SO2, CH3OH, OCN-, NH4+, and HCOOH. A tentative detection of N2O ice (7.75 mu m), forsterite dust (11.2 mu m), and CH3+ gas emission (7.18 mu m) in the primary source was also made. Compared with the two lines of sight towards background stars in the Chameleon I molecular cloud, the protostar exhibits similar ice abundances, except in the case of the ions that are higher in IRS4A. The most clear differences are the absence of the 7.2 and 7.4 mu m absorption features due to HCOO- and icy complex organic molecules in IRS4A. There is also evidence of thermal processing in both IRS4A and IRS4B, as probed by the CO2 ice features. Conclusions. We conclude that the binary protostellar system Ced 110 IRS4A and IRS4B has a large inventory of icy species. The similar ice abundances in comparison to the starless regions in the same molecular cloud suggests that the chemical conditions of the protostar were set at earlier stages in the molecular cloud. It is also possible that the source inclination and complex geometry cause a low column density along the line of sight, which hides the bands at 7.2 and 7.4 mu m. Finally, we highlight that a comprehensive analysis using radiative transfer modelling is needed to disentangle the spectral energy distributions of these sources.

This work focuses on the ice features toward the binary protostellar system Ced 110 IRS 4A and 4B, and observed with JWST as part of the Early Release Science Ice Age collaboration. We aim to explore the JWST observations of the binary protostellar system Ced 110 IRS4A and IRS4B to unveil and quantify the ice inventories toward these sources. We compare the ice abundances with those found for the same molecular cloud. The analysis is performed by fitting or comparing laboratory infrared spectra of ices to the observations. Spectral fits are carried out with the ENIIGMA fitting tool that searches for the best fit. For Ced 110 IRS4B, we detected the major ice species H_2O, CO, CO_2 and NH_3. All species are found in a mixture except for CO and CO_2, which have both mixed and pure ice components. In the case of Ced 110 IRS4A, we detected the same major species as in Ced 110 IRS4B, as well as the following minor species CH_4, SO_2, CH_3OH, OCN^-, NH_4^+ and HCOOH. Tentative detection of N_2O ice (7.75 μm), forsterite dust (11.2 μm) and CH_3^+ gas emission (7.18 μm) in the primary source are also presented. Compared with the two lines of sight toward background stars in the Chameleon I molecular cloud, the protostar has similar ice abundances, except in the case of the ions that are higher in IRS4A. The clearest differences are the absence of the 7.2 and 7.4 μm absorption features due to HCOO^- and icy complex organic molecules in IRS4A and evidence of thermal processing in both IRS4A and IRS4B as probed by the CO_2 ice features. We conclude that the binary protostellar system Ced 110 IRS4A and IRS4B has a large inventory of icy species. The similar ice abundances in comparison to the starless regions in the same molecular cloud suggest that the chemical conditions of the protostar were set at earlier stages in the molecular cloud.

(Abridged) Recent molecular surveys have revealed a rich gas organization of sonic-like fibers in all kind of environments prior to the formation of low- and high-mass stars. This paper introduces the EMERGE project aiming to investigate whether complex fiber arrangements could explain the origin of high-mass stars and clusters. We analyzed the EMERGE Early ALMA Survey including 7 star-forming regions in Orion (OMC-1/2/3/4 South, L1641N, NGC2023, and Flame Nebula) homogeneously surveyed in both molecular lines (N_2H^+ J=1-0, HNC J=1-0, plus HC3N J=10-9) and 3mm-continuum using a combination of interferometric ALMA mosaics and IRAM-30m single-dish (SD) maps. Based on our low-resolution (SD) observations, we describe the global properties of our sample covering a wide range of physical conditions including low-, intermediate, and high-mass star-forming regions in different evolutionary stages. Their comparison with ancillary YSO catalogs denotes N_2H^+ as the best proxy for the dense, star-forming gas in our targets showing a constant star formation efficiency and a fast time evolution of <1 Myr. While apparently clumpy and filamentary in our SD data, all targets show a much more complex fibrous substructure at the enhanced resolution of our ALMA+IRAM-30m maps. A large number of filamentary features at sub-parsec scales are clearly recognized in the high-density gas traced by N_2H^+ directly connected to the formation of individual protostars. This complex gas organization appears to extend further into the more diffuse gas traced by HNC. This paper presents the EMERGE Early ALMA survey including a first data release of continuum maps and spectral products for this project to be analysed in future papers of this series. A first look at these results illustrates the need of advanced data combination techniques to investigate the intrinsic multi-scale, gas structure of the ISM.

Filaments are believed to play a key role in high-mass star formation. We present a systematic study of the filaments and their hosting clumps in the G35 molecular complex using James Clerk Maxwell Telescope SCUBA-2 850 mu m continuum data. We identified five clouds in the complex and 91 filaments within them, some of which form 10 hub-filament systems (HFSs), each with at least three hub-composing filaments. We also compiled a catalog of 350 dense clumps, 183 of which are associated with the filaments. We investigated the physical properties of the filaments and clumps, such as mass, density, and size, and their relation to star formation. We find that the global mass-length trend of the filaments is consistent with a turbulent origin, while the hub-composing filaments of high line masses (ml >230 M-circle dot pc(-1)) in HFSs deviate from this relation, possibly due to feedback from massive star formation. We also find that the most massive and densest clumps (R >0.2 pc, M >35 M-circle dot, Sigma>0.05gcm(2)) are located in the filaments and in the hubs of HFSs, with the latter bearing a higher probability of the occurrence of high-mass star-forming signatures, highlighting the preferential sites of HFSs for high-mass star formation. We do not find significant variation in the clump mass surface density across different evolutionary environments of the clouds, which may reflect the balance between mass accretion and stellar feedback.

Context. Protostellar outflows exhibit large variations in their structure depending on the observed gas emission. To understand the origin of the observed variations, it is important to analyze the differences in the observed morphology and kinematics of the different tracers. The James Webb Space Telescope (JWST) allows us to study the physical structure of the protostellar outflow through well-known near-infrared shock tracers in a manner unrivaled by other existing ground-based and space-based telescopes at these wavelengths. Aims. This study analyzes the atomic jet and molecular outflow in the Class I protostar, TMC1A, utilizing spatially resolved [Fe II] and H2 lines to characterize the morphology and to identify previously undetected spatial features, and compare them to existing observations of TMC1A and its outflows observed at other wavelengths. Methods. We identified a large number of [Fe II] and H2 lines within the G140H, G235H, and G395H gratings of the NIRSpec IFU observations. We analyzed their morphology and position-velocity (PV) diagrams. From the observed [Fe II] line ratios, the extinction toward the jet is estimated. Results. We detected the bipolar Fe jet by revealing, for the first time, the presence of a redshifted atomic jet. Similarly, the red-shifted component of the H2 slower wide-angle outflow was observed. The [Fe II] and H2 redhifted emission both exhibit significantly lower flux densities compared to their blueshifted counterparts. Additionally, we report the detection of a collimated high-velocity (~100 km s−1), blueshifted H2 outflow, suggesting the presence of a molecular jet in addition to the well-known wider angle low-velocity structure. The [Fe II] and H2 jets show multiple intensity peaks along the jet axis, which may be associated with ongoing or recent outburst events. In addition to the variation in their intensities, the H2 wide-angle outflow exhibits a ring-like structure. The blueshifted H2 outflow also shows a left-right brightness asymmetry likely due to interactions with the surrounding ambient medium and molecular outflows. Using the [Fe II] line ratios, the extinction along the atomic jet is estimated to be between AV = 10–30 on the blueshifted side, with a trend of decreasing extinction with distance from the protostar. A similar AV is found for the redshifted side, supporting the argument for an intrinsic red-blue outflow lobe asymmetry rather than environmental effects such as extinction. This intrinsic difference revealed by the unprecedented sensitivity of JWST, suggests that younger outflows already exhibit the red-blue side asymmetry more commonly observed toward jets associated with Class II disks.

(abridged) Protostellar outflows exhibit large variations in their structure depending on the observed gas emission. This study analyzes the atomic jet and molecular outflow in the Class I protostar, TMC1A to characterize morphology and identify previously undetected spatial features with JWST's NIRSpec IFU. In addition to identifying a large number of Fe II and H2 lines, we have detected the bipolar Fe jet by revealing, for the first time, the presence of a red-shifted atomic jet. Similarly, the red-shifted component of the H2 slower wide-angle outflow is observed. Both Fe II and H2 red-shifted emission exhibit significantly lower flux densities compared to their blue-shifted counterparts. Additionally, we report the detection of a collimated high-velocity (100 km s-1), blue-shifted H2 outflow, suggesting the presence of a molecular jet in addition to the well-known wider angle low-velocity structure. The Fe II and H2 jets show multiple intensity peaks along the jet axis, which may be associated with ongoing or recent outburst events. In addition to the variation in their intensities, the H2 wide-angle outflow exhibits a "ring"-like structure. The blue-shifted H2 outflow also shows a left-right brightness asymmetry likely due to interactions with the surrounding ambient medium and molecular outflows. Using the Fe II line ratios, the extinction along the atomic jet is estimated to be between Av = 10-30 on the blue-shifted side, with a trend of decreasing extinction with distance from the protostar. A similar Av is found for the red-shifted side, supporting the argument for an intrinsic red-blue outflow lobe asymmetry rather than environmental effects such as extinction. This intrinsic difference revealed by the unprecedented sensitivity of JWST, suggests that younger outflows already exhibit the red-blue side asymmetry more commonly observed towards jets associated with Class II disks.

Clouds of gas and dust in the Galaxy are nurseries in which stars and planetary systems are born. During their journey from the diffuse interstellar medium to the protoplanetary disks, molecular solids accumulate on cold dust grains by accretion and surface chemistry. These so-called icy grains will continuously evolve, notably by collision and aggregation processes, modifying their sizes. Our ‘Ice Age’ James Webb Space Telescope observations of the dense Chamaeleon I cloud reveal that this growth starts early, before the protostellar phase, substantially modifying the ice band profiles in the spectra. Spectral analysis confirms that the grains reach micrometre sizes, implying myriad changes in local microphysics, including mass transfer from small to large grains, reduction in the grain surface available for chemistry and modification of the penetration and propagation of radiation fields. Deformation of the observed profiles complicates the determination of chemical abundance. Observing the extensive icy grain growth in dense clouds quantitatively constrains the grain size evolution before star and planet formation. Cold ice-covered dust grains grow during their journey from the interstellar medium to protoplanetary disks. JWST observations show that this growth begins before the protostellar phase and provide quantitative insights into the grain growth process.

Planet formation is strongly influenced by the composition and distribution of volatiles within protoplanetary disks. With JWST, it is now possible to obtain direct observational constraints on disk ices, as recently demonstrated by the detection of ice absorption features toward the edge-on HH 48 NE disk as part of the Ice Age Early Release Science program. Here, we introduce a new radiative transfer modeling framework designed to retrieve the composition and mixing status of disk ices using their band profiles, and apply it to interpret the H2O, CO2, and CO ice bands observed toward the HH 48 NE disk. We show that the ices are largely present as mixtures, with strong evidence for CO trapping in both H2O and CO2 ice. The HH 48 NE disk ice composition (pure versus polar versus apolar fractions) is markedly different from earlier protostellar stages, implying thermal and/or chemical reprocessing during the formation or evolution of the disk. We infer low ice-phase C/O ratios around 0.1 throughout the disk, and also demonstrate that the mixing and entrapment of disk ices can dramatically affect the radial dependence of the C/O ratio. It is therefore imperative that realistic disk ice compositions are considered when comparing planetary compositions with potential formation scenarios, which will fortunately be possible for an increasing number of disks with JWST.