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Water is a fundamental molecule in the star and planet formation process, essential for catalysing the growth of solid material and the formation of planetesimals within disks 1 , 2 . However, the water snowline and the HDO:H 2 O ratio within proto-planetary disks have not been well characterized because water only sublimates at roughly 160 K (ref. 3 ), meaning that most water is frozen out onto dust grains and that the water snowline radii are less than 10 AU (astronomical units) 4 , 5 . The sun-like protostar V883 Ori (M *  = 1.3  M ⊙ ) 6 is undergoing an accretion burst 7 , increasing its luminosity to roughly 200  L ⊙ (ref. 8 ), and previous observations suggested that its water snowline is 40–120 AU in radius 6 , 9 , 10 . Here we report the direct detection of gas phase water (HDO and H 2 18 O ) from the disk of V883 Ori. We measure a midplane water snowline radius of approximately 80 AU, comparable to the scale of the Kuiper Belt, and detect water out to a radius of roughly 160 AU. We then measure the HDO:H 2 O ratio of the disk to be (2.26 ± 0.63) × 10 −3 . This ratio is comparable to those of protostellar envelopes and comets, and exceeds that of Earth’s oceans by 3.1 σ . We conclude that disks directly inherit water from the star-forming cloud and this water becomes incorporated into large icy bodies, such as comets, without substantial chemical alteration. Direct detection of gas phase water from the disk of V883 Ori indicates that disks directly inherit water from the star-forming cloud that becomes incorporated into large icy bodies without notable chemical alteration.

The size of a disk encodes important information about its evolution. Combining new Submillimeter Array observations with archival Atacama Large Millimeter/submillimeter Array data, we analyze millimeter continuum and CO emission line sizes for a sample of 44 protoplanetary disks around stars with masses of 0.15–2 M ⊙ in several nearby star-forming regions. Sizes measured from 12CO line emission span from 50 to 1000 au. This range could be explained by viscous evolution models with different α values (mostly of 10−4–10−3) and/or a spread of initial conditions. The CO sizes for most disks are also consistent with MHD wind models that directly remove disk angular momentum, but very large initial disk sizes would be required to account for the very extended CO disks in the sample. As no CO size evolution is observed across stellar ages of 0.5–20 Myr in this sample, determining the dominant mechanism of disk evolution will require a more complete sample for both younger and more evolved systems. We find that the CO emission is universally more extended than the continuum emission by an average factor of 2.9 ± 1.2. The ratio of the CO to continuum sizes does not show any trend with stellar mass, millimeter continuum luminosity, or the properties of substructures. The GO Tau disk has the most extended CO emission in this sample, with an extreme CO-to-continuum size ratio of 7.6. Seven additional disks in the sample show high size ratios (≳4) that we interpret as clear signs of substantial radial drift.

Nearly half of all stars similar to our Sun are in binary or multiple systems 1 , which may affect the evolution of the stars and their protoplanetary disks during their earliest stages. NGC 1333-IRAS2A is a young, Class 0, low-mass protostellar system located in the Perseus molecular cloud 2 . It is known to drive two bipolar outflows that are almost perpendicular to each other on the sky 3 , 4 and is resolved into binary components, VLA1 and VLA2, through long wavelength continuum observations 5 . Here we report spatially and spectrally resolved observations of a range of molecular species. We compare these to detailed magnetohydrodynamic simulations: the comparisons show that inhomogeneous accretion onto the circumstellar disks occurs in episodic bursts, driving a wobbling jet. We conclude that binarity and multiplicity in general strongly affect the properties of the emerging stars, as well as the physical and chemical structures of the protoplanetary disks and therefore potentially any emerging planetary systems. Binarity and multiplicity in general strongly affect the properties of emerging stars, as well as the physical and chemical structures of protoplanetary disks and therefore potentially any emerging planetary systems.

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 (H2, CH3, CH4, C2H2, 13CCH2, C2H4, C2H6, C3H4, C4H2, C6H6, HCN, HC3N, CO2, and 13CO2) 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 H2 and Ne gas strongly supports that J0446B hosts a long-lived primordial disk, rather than a debris disk. The marginal H2O detection and the high C2H2/CO2 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.

Most stars form in multiple-star systems. For a better understanding of their formation processes, it is important to resolve the individual protostellar components and the surrounding envelope and disk material at the earliest possible formation epoch, because the formation history can be lost in a few orbital timescales. Here we present Atacama Large Millimeter/submillimeter Array observational results of a young multiple protostellar system, IRAS 04239+2436, where three well-developed large spiral arms were detected in the shocked SO emission. Along the most conspicuous arm, the accretion streamer was also detected in the SO2 emission. The observational results are complemented by numerical magnetohydrodynamic simulations, where those large arms only appear in magnetically weakened clouds. Numerical simulations also suggest that the large triple spiral arms are the result of gravitational interactions between compact triple protostars and the turbulent infalling envelope.

High angular resolution imaging by Atacama Large Millimeter/submillimeter Array (ALMA) has revealed the near universality and diversity of substructures in protoplanetary disks. However, disks around M-type pre-main-sequence stars are still poorly sampled, despite the prevalence of M dwarfs in the Galaxy. Here we present high-resolution (∼50 mas, 8 au) ALMA Band 6 observations of six disks around mid-M stars in Taurus. We detect dust continuum emission in all six disks, 12CO in five disks, and 13CO line in two disks. The size ratios between gas and dust disks range from 1.6 to 5.1. The ratio of about 5 for 2M0436 and 2M0450 indicates efficient dust radial drift. Four disks show rings and cavities, and two disks are smooth. The cavity sizes occupy a wide range: 60 au for 2M0412, and ∼10 au for 2M0434, 2M0436, and 2M0508. Detailed visibility modeling indicates that small cavities of 1.7 and 5.7 au may hide in the two smooth disks 2M0450 and CIDA 12. We perform radiative transfer fitting of the infrared spectral energy distributions to constrain the cavity sizes, finding that micron-sized dust grains may have smaller cavities than millimeter grains. Planet–disk interactions are the preferred explanation to produce the large 60 au cavity, while other physics could be responsible for the three ∼10 au cavities under current observations and theories. Currently, disks around mid- to late M stars in Taurus show a higher detection frequency of cavities than earlier-type stars, although a more complete sample is needed to evaluate any dependence of substructure on stellar mass.

The growth of dust grains in protoplanetary disks is a necessary first step towards planet formation 1 . This growth has been inferred from observations of thermal dust emission 2 towards mature protoplanetary systems (age >2 million years) with masses that are, on average, similar to Neptune 3 . In contrast, the majority of confirmed exoplanets are heavier than Neptune 4 . Given that young protoplanetary disks are more massive than their mature counterparts, this suggests that planet formation starts early, but evidence for grain growth that is spatially and temporally coincident with a massive reservoir in young disks remains scarce. Here, we report observations on a lack of emission of carbon monoxide isotopologues within the inner ~15 au of a very young (age ~100,000 years) disk around the solar-type protostar TMC1A. By using the absence of spatially resolved molecular line emission to infer the gas and dust content of the disk, we conclude that shielding by millimetre-size grains is responsible for the lack of emission. This suggests that grain growth and millimetre-size dust grains can be spatially and temporally coincident with a mass reservoir sufficient for giant planet formation. Hence, planet formation starts during the earliest, embedded phases in the life of young stars. Evidence for the earliest phase of planet formation, dust grain growth, has been seen in the very young and massive circumstellar disk around low-mass protostar TMC1A. Such systems, still rich in gas, are responsible for the high-mass end of the exoplanet mass distribution.

While the most exciting explanation of the observed dust asymmetries in protoplanetary disks is the presence of protoplanets, other mechanisms can also form the dust features. This paper presents dual-wavelength Atacama Large Millimeter/submillimeter Array observations of a large asymmetric dusty ring around the M-type star CIDA 9A. We detect a dust asymmetry in both 1.3 and 3.1 mm data. To characterize the asymmetric structure, a parametric model is used to fit the observed visibilities. We report a tentative azimuthal shift of the dust emission peaks between the observations at the two wavelengths. This shift is consistent with a dust trap caused by a vortex, which may be formed by an embedded protoplanet or other hydrodynamical instabilities, such as a dead zone. Deep high-spatial-resolution observations of dust and molecular gas are needed to constrain the mechanisms that formed the observed millimeter cavity and dust asymmetry in the protoplanetary disk around CIDA 9A.

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.

While protoplanetary disks are often treated as isolated systems in planet formation models, observations increasingly suggest that vigorous interactions between Class II disks and their environments are not rare. DO Tau is a T Tauri star that has previously been hypothesized to have undergone a close encounter with the HV Tau system. As part of the DESTINYS ESO Large Programme, we present new Very Large Telescope (VLT)/SPHERE polarimetric observations of DO Tau and combine them with archival Hubble Space Telescope (HST) scattered-light images and Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO isotopologues and CS to map a network of complex structures. The SPHERE and ALMA observations show that the circumstellar disk is connected to arms extending out to several hundred astronomical units. HST and ALMA also reveal stream-like structures northeast of DO Tau, some of which are at least several thousand astronomical units long. These streams appear not to be gravitationally bound to DO Tau, and comparisons with previous Herschel far-IR observations suggest that the streams are part of a bridge-like structure connecting DO Tau and HV Tau. We also detect a fainter redshifted counterpart to a previously known blueshifted CO outflow. While some of DO Tau’s complex structures could be attributed to a recent disk–disk encounter, they might be explained alternatively by interactions with remnant material from the star formation process. These panchromatic observations of DO Tau highlight the need to contextualize the evolution of Class II disks by examining processes occurring over a wide range of size scales.