Giant Planet Formation Research Articles

The outcome of collisions between gaseous clumps formed by disk instability

The disk instability model is a promising pathway for giant planet formation in various conditions. At the moment, population synthesis models are used to investigate the outcomes of this theory, where a key ingredient of the disk population evolution are collisions of self-gravitating clumps formed by the disk instabilities. In this study, we explored the wide range of dynamics between the colliding clumps by performing state-of-the-art smoothed particle hydrodynamics simulations with a hydrogen-helium mixture equation of state and investigated the parameter space of collisions between clumps of different ages, masses (1–10 Jupiter mass), various impact conditions (head-on to oblique collisions) and a range of relative velocities. We find that the perfect merger assumption used in population synthesis models is rarely satisfied and that the outcomes of most of the collisions lead to erosion, disruption or a hit-and-run. We also show that in some cases collisions can initiate the dynamical collapse of the clump. We conclude that population synthesis models should abandon the simplifying assumption of perfect merging. Relaxing this assumption will significantly affect the inferred population of planets resulting from the disk instability model.

BOWIE-ALIGN: how formation and migration histories of giant planets impact atmospheric compositions

ABSTRACT Hot Jupiters present a unique opportunity for measuring how planet formation history shapes present-day atmospheric composition. However, due to the myriad pathways influencing composition, a well-constructed sample of planets is needed to determine whether formation history can be accurately traced back from atmospheric composition. To this end, the BOWIE-ALIGN survey (A spectral Light Investigation into hot gas Giant origiNs by the collaboration of Bristol, Oxford, Warwick, Imperial, Exeter, +) will compare the compositions of eight hot Jupiters around F stars, four with orbits aligned with the stellar rotation axis, and four misaligned. Using the alignment as an indicator for planets that underwent disc migration or high-eccentricity migration, one can determine whether migration history produces notable differences in composition between the two samples of planets. This paper describes the planet formation model that motivates our observing programme. Our model traces the accretion of chemical components from the gas and dust in the disc over a broad parameter space to create a full, unbiased model sample from which we can estimate the range of final atmospheric compositions. For high metallicity atmospheres ($\mathrm{ O}\mathrm{ /H}\ge 10 \times$ solar), the C/O ratios of aligned and misaligned planets diverge, with aligned planets having lower C/O ($\lt 0.25$) due to the accretion of oxygen-rich silicates from the inner disc. However, silicates may rain out instead of releasing their oxygen into the atmosphere. This would significantly increase the C/O of aligned planets (C/O $\gt 0.6$), inverting the trend between the aligned and misaligned planets. Nevertheless, by comparing statistically significant samples of aligned and misaligned planets, we expect atmospheric composition to constrain how planets form.

A Thermodynamic Criterion for the Formation of Circumplanetary Disks

The formation of circumplanetary disks is central to our understanding of giant planet formation, influencing their growth rate during the post-runaway phase and observability while embedded in protoplanetary disks. We use three-dimensional global multifluid radiation hydrodynamics simulations with the FARGO3D code to define the thermodynamic conditions that enable circumplanetary disk formation around Jovian planets on wide orbits. Our simulations include stellar irradiation, viscous heating, static mesh refinement, and active calculation of opacity based on multifluid dust dynamics. We find a necessary condition for the formation of circumplanetary disks in terms of a mean cooling time: When the cooling time is at least 1 order of magnitude shorter than the orbital timescale, the specific angular momentum of the gas is nearly Keplerian at scales of one-third of the Hill radius. We show that the inclusion of multifluid dust dynamics favors rotational support because dust settling produces an anisotropic opacity distribution that favors rapid cooling. In all our models with radiation hydrodynamics, specific angular momentum decreases as time evolves, in agreement with the formation of an inner isentropic envelope due to compressional heating. The isentropic envelope can extend up to one-third of the Hill radius and shows negligible rotational support. Thus, our results imply that young gas giant planets may host spherical isentropic envelopes, rather than circumplanetary disks.

Radiative signatures of circumplanetary disks and envelopes during the late stages of giant planet formation

During the late stages of giant planet formation, protoplanets are surrounded by a circumplanetary disk and an infalling envelope of gas and dust. For systems with sufficient cooling, material entering the sphere of influence of the planet falls inward and approaches ballistic conditions. Due to conservation of angular momentum, most of the incoming material falls onto the disk rather than directly onto the planet. This paper determines the spectral energy distributions of forming planets in this stage of evolution. Generalizing previous work, we consider a range of possible geometries for the boundary conditions of the infall and determine the two-dimensional structure of the envelope, as well as the surface density of the disk. After specifying the luminosity sources for the planet and disk, we calculate the corresponding radiative signatures for the system, including the emergent spectral energy distributions and emission maps. These results show how the observational appearance of forming planets depend on the input parameters, including the instantaneous mass, mass accretion rate, semimajor axis of the orbit, and the planetary magnetic field strength (which sets the inner boundary condition for the disk). We also consider different choices for the form of the opacity law and attenuation due to the background circumstellar disk. Although observing forming planets will be challenging, these results show how the observational signatures depend on the underlying properties of the planet/disk/envelope system.

Suppression of giant planet formation around low-mass stars in clustered environments

Context. Current exoplanet formation studies tend to overlook the birth environment of stars in clustered environments. However, the effects of this environment on the planet formation process are important, especially in the earliest stage. Aims. We investigate the differences in planet populations forming in star-cluster environments through pebble accretion and compare these results with planet formation around isolated stars. We strive to provide potential signatures of the young planetary systems to guide future observations. Methods. We present a new planet population synthesis code designed for clustered environments. This planet formation model is based on pebble accretion and includes migration in the circumstellar disk. The disk’s gas and dust have been evolved via 1D simulations, while considering the effects of photo-evaporation of the nearby stars. Results. Planetary systems in a clustered environment are different than those born in isolation; the environmental effects are important for a wide range of observable parameters and the eventual architecture of the planetary systems. Planetary systems born in a clustered environment lack cold Jupiters, as compared to isolated planetary systems. This effect is more pronounced for low-mass stars (≲0.2 M⊙). On the other hand, planetary systems born in clusters show an excess of cold Neptune around these low-mass stars. Conclusions. In future observations, finding an excess of cold Neptunes and a lack of cold Jupiters could be used to constrain the birth environments of these planetary systems. Exploring the dependence of cold Jupiter’s intrinsic occurrence rate on stellar mass offers insights into the birth environment of their proto-embryos.

Outflow Driven by a Protoplanet Embedded in the TW Hya Disk

Gas giant planets are formed by gas accretion onto planetary cores in protoplanetary disks. However, direct evidence of this process is still lacking, limiting our understanding of planetary formation processes. During mass accretion, planet-driven outflows may be launched, which could be observable by shock tracers such as sulfur monoxide (SO). We report the detection of SO gas in the protoplanetary disk around TW Hya in archival Atacama Large Millimeter/submillimeter Array observations. The SO J = 87 − 76 emission line is detected at a 6σ significance and localized to the southeast region of the disk with an arc-like morphology. The line center is redshifted with respect to the systemic velocity by ∼5 km s−1. The starting point of the SO emission is located at a planet-carved dust gap at 42 au. We attribute this to an outflow driven by an embedded protoplanet. Indeed, the observed morphology is well reproduced by a ballistic outflow model. The outflow velocity suggests that the outflow launching source has a mass of ∼4M ⊕ and the mass-loss rate is 3 × 10−8–1 × 10−6 M Jup yr−1. With the relation of mass-loss and mass-accretion rates established for protostars, we estimated the mass-accretion rate onto the protoplanet to be 3 × 10−7−1 × 10−5 M Jup yr−1, which matches theoretical predictions for a ∼4M ⊕ planet at this separation. The detection of planet-driven outflow provides us a unique opportunity to directly probe the earliest phase of gas giant planet formation.

Giant planet formation in the Solar System

The formation history of Jupiter has been of interest due to its ability to shape the solar system’s history. Yet little attention has been paid to the formation and growth of Saturn and the other giant planets. Here we explore through N-body simulations the implications of the simplest disc and pebble accretion model with steady-state accretion and an assumed ring structure in the disc at 5 AU on the formation of the giant planets in the solar system. We conducted a statistical survey of different disc parameters and initial conditions of the protoplanetary disc to establish which combination best reproduces the present outer solar system. We examined the effect of the initial planetesimal disc mass, the number of planetesimals and their size-frequency distribution slope, pebble accretion prescription and sticking efficiency on the likelihood of forming gas giants and their orbital distribution. The results reveal that the accretion sticking efficiency is the most sensitive parameter to control the final masses and number of giant planets. We have been unable to replicate the formation of all three types of giant planets in the solar system in a single simulation. The probability distribution of the final location of the giant planets is approximately constant in logr, suggesting there is a slight preference for formation closer to the Sun but no preference for more massive planets to form closer. The eccentricity distribution has a higher mean for more massive planets indicating that systems with more massive planets are more violent. We compute the average formation time for proto-Jupiter to reach 10 Earth masses to be 〈tc,J〉=1.1±0.3 Myr and for proto-Saturn 〈tc,S〉=3.3±0.4 Myr, while for the ice giants this increases to 〈tc,I〉=4.9±0.1 Myr. The formation timescales of the cores of the gas giants are distinct at >95% confidence, suggesting that they formed sequentially.

Sequential giant planet formation initiated by disc substructure

Context. Planet formation models are necessary to understand the origins of diverse planetary systems. Circumstellar disc substructures have been proposed as preferred locations of planet formation, but a complete formation scenario has not been covered by a single model so far. Aims. We aim to study the formation of giant planets facilitated by disc substructure and starting with sub-micron-sized dust. Methods. We connect dust coagulation and drift, planetesimal formation, N-body gravity, pebble accretion, planet migration, planetary gas accretion, and gap opening in one consistent modelling framework. Results. We find rapid formation of multiple gas giants from the initial disc substructure. The migration trap near the substructure allows for the formation of cold gas giants. A new pressure maximum is created at the outer edge of the planetary gap, which triggers the next generation of planet formation resulting in a compact chain of giant planets. A high planet formation efficiency is achieved, as the first gas giants are effective at preventing dust from drifting further inwards, which preserves material for planet formation. Conclusions. Sequential planet formation is a promising framework to explain the formation of chains of gas and ice giants.

TOI-2447 b / NGTS-29 b: a 69-day Saturn around a Solar analogue

ABSTRACT Discovering transiting exoplanets with relatively long orbital periods (>10 d) is crucial to facilitate the study of cool exoplanet atmospheres (Teq < 700 K) and to understand exoplanet formation and inward migration further out than typical transiting exoplanets. In order to discover these longer period transiting exoplanets, long-term photometric, and radial velocity campaigns are required. We report the discovery of TOI-2447 b (=NGTS-29 b), a Saturn-mass transiting exoplanet orbiting a bright (T = 10.0) Solar-type star (Teff = 5730 K). TOI-2447 b was identified as a transiting exoplanet candidate from a single transit event of 1.3 per cent depth and 7.29 h duration in TESS Sector 31 and a prior transit event from 2017 in NGTS data. Four further transit events were observed with NGTS photometry which revealed an orbital period of P = 69.34 d. The transit events establish a radius for TOI-2447 b of $0.865 \pm 0.010\, \rm R_{\rm J}$, while radial velocity measurements give a mass of $0.386 \pm 0.025\, \rm M_{\rm J}$. The equilibrium temperature of the planet is 414 K, making it much cooler than the majority of TESS planet discoveries. We also detect a transit signal in NGTS data not caused by TOI-2447 b, along with transit timing variations and evidence for a ∼150 d signal in radial velocity measurements. It is likely that the system hosts additional planets, but further photometry and radial velocity campaigns will be needed to determine their parameters with confidence. TOI-2447 b/NGTS-29 b joins a small but growing population of cool giants that will provide crucial insights into giant planet composition and formation mechanisms.

Formation of Giant Planets by Gas Disk Gravitational Instability on Wide Orbits around Protostars with Varied Masses. II. Quadrupled Spatial Resolution and Beta Cooling

Exoplanet demographics are sufficiently advanced to provide important constraints on theories of planet formation. While core and pebble accretion are preferred for rocky and icy planets, there appears to be a need for gas disk gravitational instability (GDGI) to play a role in the formation of M-dwarf gas giants and those orbiting at large distances. Here we present GDGI models that go beyond those presented by Boss (2011) dealing with the formation of wide-orbit gas giants. The new models use quadrupled spatial resolution, in both the radial and azimuthal directions, to reduce the effects of finite spatial resolution. The new models also employ the β cooling approximation, instead of the diffusion approximation used by Boss (2011), in order to push the models further in time. As in Boss (2011), the central protostars have masses of 0.1, 0.5, 1.0, 1.5, or 2.0 M ⊙, surrounded by disks with masses ranging from 0.019 M ⊙ to 0.21 M ⊙. For each case, two models are computed, one with an initial minimum Toomre Q stability value ranging from 1.1 to 1.7, and one with a higher initial disk temperature, resulting in the initial minimum Q ranging from 2.2 to 3.4. These new models continue to show that GDGI can explain the formation of gas giants at distances of ∼30 to ∼50 au on eccentric orbits (e less than ∼0.2), though the number formed drops to 0 as the protostar mass decreases to 0.1 M ⊙.

Direct imaging of exoplanets: Legacy and prospects

Understanding how giant and terrestrial planets form and evolve, what is their internal structure and that of their atmosphere, represents one of the major challenges of modern astronomy, which is directly connected to the ultimate search for life at the horizon 2030–2050. However, several astrophysical (understanding of the formation and physics of giant and terrestrial exoplanets), biological (identification of the best biomarkers) and technological (technical innovations for the new generations of telescopes and instruments) obstacles must be overcome. From the astrophysical point of view, it is indeed crucial to understand the mechanisms of formation and evolution of giant planets, including planet and disk interactions, which will completely sculpt the planetary architectures and thus dominate the formation of terrestrial planets, especially in regions around the host star capable of supporting life. It is also important to develop dedicated instrumentation and techniques to study in their totality the population of giant and terrestrial planets, but also to reveal in the near future the first biological markers of life in the atmospheres of terrestrial planets. In that perspective, direct imaging from ground-based observatories or in space is playing a central role in concert with other observing techniques. In this paper, I will briefly review the genesis of this observing technique, the main instrumental innovation and challenges, stellar targets and surveys, to then present the main results obtained so far about the physics and the mechanisms of formation and evolution of young giant planets and planetary system architectures. I will then present the exciting perspectives offered by the upcoming generation of planet imagers about to come online, particularly on the future extremely large telescopes. On the timescale of a human Life, we may well be witnessing the first discovery of an exoplanet and the first detection of indices of life in the atmosphere of a nearby exo-Earth!

Study of type II migration under the framework of the disk instability model for giant planet formation

Context. Hydrodynamic simulations of the migration of planets formed by gravitational instability suggest that after an initial phase of fast migration, planets can open gaps and continue to migrate on a type II migration timescale. The simulation time length is typically on the order of 104 yr. Aims. We study the effects of the subsequent type II migration during the disk lifetime on the final orbital radii of planets. Methods. We used a numerical disk model that follows the disk formation and evolution. The disk acquires mass through the mass influx from the collapse of its parent molecular cloud core. The model reflects the influence of the properties of the parent core on the disk. Considering clumps forming at different times in a disk and also in different disks with different parent core properties, we used the type II migration rate to follow the clump migration from the formation location. We studied the dependence of the clump migration on the properties of the parent core. Results. The mass influx drag enhances the migration process. The duration and viscosity of gravitational instability, viscosity in the dead zone, and the collapse time of the parent core play important roles in planet migration. As the angular momentum and mass of the parent core increase, migration is enhanced. The final radius is sensitive to the initial radius. Clumps forming at large radii might migrate outward with the disk expansion. Conclusions. Even though type II migration is slow, clumps can migrate over significant distances. A considerable proportion of clumps migrate to the central protostar via type II migration. Our calculations support the idea that the observed pile-up of planets at <0.3 AU is explained by a scenario where planets might form at large radii, then migrate to orbits of <0.3 AU, and halt by a stopping mechanism at this location.

Mid-infrared Spectrum of the Disk around the Forming Companion GQ Lup B Revealed by JWST/MIRI

GQ Lup B is a forming brown dwarf companion (M ∼ 10–30 M J) showing evidence for an infrared excess associated with a disk surrounding the companion itself. Here we present mid-infrared (MIR) observations of GQ Lup B with the Medium Resolution Spectrometer (MRS) on JWST, spanning 4.8–11.7 μm. We remove the stellar contamination using reference differential imaging based on principal component analysis, demonstrating that the MRS can perform high-contrast science. Our observations provide a sensitive probe of the disk surrounding GQ Lup B. We find no sign of a silicate feature, similar to other disks surrounding very low-mass objects, which likely implies significant grain growth ( amin≳5 μm) and potentially dust settling. Additionally, we find that if the emission is dominated by an inner wall, the disk around the companion might have an inner cavity larger than the one set by sublimation. Conversely, if our data probe the emission from a thin flat disk, we find the disk to be very compact. More observations are required to confirm this findings and assess the vertical structure of the disk. This approach paves the path to the future study of circumplanetary disks and their physical properties. Our results demonstrate that MIR spectroscopic observations can reveal the physical characteristics of disks around forming companions, providing unique insights into the formation of giant planets, brown dwarfs, and their satellites.

Growth and evolution of low-mass planets in pressure bumps

Observations of protoplanetary disks have revealed dust rings that are likely due to the presence of pressure bumps in the disk. Because these structures tend to trap drifting pebbles, it has been proposed that pressure bumps may play an important role in the planet formation process. In this paper, we investigate the orbital evolution of a 0.1 M⊕ protoplanet embedded in a pressure bump using 2D hydrodynamical simulations of protoplanetary disks consisting of gas and pebbles. We examine the role of thermal forces generated by the pebble accretion-induced heat release, taking into account the feedback between the luminosity and the eccentricity. We also study the effect of the pebble-scattered flow on the planet’s orbital evolution. Due to the accumulation of pebbles at the pressure bump, the planet’s accretion luminosity is high enough to induce significant eccentricity growth through thermal forces. Accretion luminosity is also responsible for vortex formation at the planet’s position through baroclinic effects, which cause the planet to escape from the dust ring if dust feedback on the gas is neglected. Including the effect of the dust feedback leads to weaker vortices, which enable the planet to remain close to the pressure maximum on an eccentric orbit. Simulations in which the planet mass is allowed to increase as a consequence of pebble accretion result in the formation of giant planet cores with masses in the range of 5–20 M⊕ over ~2 × 104 yr. This occurs for moderate values of the Stokes number, St ≈ 0.01, such that the pebble drift velocity is not too high and the dust ring mass not too small. Our results suggest that pressure bumps mays be preferred locations for the formation of giant planets, but this requires a moderate level of grain growth within the disk.

A Review to the Observational and Theoretical Studies of Planetary Systems around Red Dwarfs

Red dwarfs are one of the smallest and dimmest main-sequence stars. With the improvement of observation technology, a rich population of planets have been discovered around them, which exhibits distinct distribution characteristics from the planets around Solar-like stars. Earth-like planets have a higher occurrence rate around red dwarfs, and the planetary systems are tightly compact. The closer habitable zone makes it easier to search for habitable planets. The distribution of the radius valley between super-Earths and sub-Neptunes also differs from that around solar-like stars. Moreover, the discovery of giant planets around these low-mass stars can be hard to explain by current leading theories of planet formation. As the mass of solid material in the protoplanetary disk decreases with decreasing stellar masses, the formation of giant planets remains challenging. The observations from telescopes such as Transiting Exoplanet Survey Satellite (TESS), James Webb, and Atacama Large Millimeter/submillimeter Array (ALMA) have provided invaluable insights and opportunities for the study of planetary formation. In this paper, we review the observations of different populations of planets and summarize the up-to-date understanding of planetary formation around red dwarfs.

Implications of the discovery of AF Lep b

Context. Dynamical masses of young planets aged between 10 and 200 Myr detected in imaging play a crucial role in shaping models of giant planet formation. Regrettably, only a few such objects possess these characteristics. Furthermore, the evolutionary pattern of young sub-stellar companions in near-infrared colour-magnitude diagrams might diverge from free-floating objects, possibly due to differing formation processes. Aims. The recent identification of a giant planet around AF Lep, part of the β Pic moving group (BPMG), encouraged us to re-examine these points. Methods. We considered updated dynamical masses and luminosities for the sub-stellar objects in the BPMG. In addition, we compared the properties of sub-stellar companions and free-floating objects in the BPMG and other young associations remapping the positions of the objects in the colour-magnitude diagram into a dustiness-temperature plane. Results. We found that cold-start evolutionary models do not reproduce the mass-luminosity relation for sub-stellar companions in the BPMG. This aligns rather closely with predictions from “hot start” scenarios and is consistent with recent planet formation models. We obtain rather good agreement with masses from photometry and the remapping approach compared to actual dynamical masses. We also found a strong suggestion that the near-infrared colour-magnitude diagram for young companions is different from that of free-floating objects belonging to the same young associations. Conclusions. If confirmed by further data, this last result would imply that cloud settling – which likely causes the transition between L and T spectral type – occurs at a lower effective temperature in young companions than in free-floating objects. This might tentatively be explained with a different chemical composition.

The PFS View of TOI-677 b: A Spin–Orbit Aligned Warm Jupiter in a Dynamically Hot System* *This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile.

TOI-677 b is part of an emerging class of “tidally detached” gas giants (a/R ⋆ ≳ 11) that exhibit large orbital eccentricities and yet low stellar obliquities. Such sources pose a challenge for models of giant planet formation, which must account for the excitation of high eccentricities without large changes in the orbital inclination. In this work, we present a new Rossiter–McLaughlin measurement of the tidally detached warm Jupiter TOI-677 b, obtained using high-precision radial velocity observations with Magellan’s Planet Finder Spectrograph (PFS). Combined with previously published observations from the Very Large Telescope’s ESPRESSO spectrograph, we derive one of the most precisely constrained sky-projected spin–orbit angle measurements to date for an exoplanet. The combined fit offers a refined set of self-consistent parameters, including a low sky-projected stellar obliquity of λ=3.°2−1.∘5+1.∘6 and a moderately high eccentricity of e=0.460−0.018+0.019 , which further constrain the puzzling architecture of this system. We examine several potential scenarios that may have produced the current TOI-677 orbital configuration, ultimately concluding that TOI-677 b most likely had its eccentricity excited through disk–planet interactions. This system adds to a growing population of aligned warm Jupiters on eccentric orbits around hot (T eff > 6100 K) stars.

Survival of the long-lived inner disk of PDS

The K7 T Tauri star remains the best laboratory for investigating the influence of giant planet formation on the structure of the parental disk. One of the most intriguing discoveries is the detection of a resolved inner disk from ALMA observations that extends up to the orbit of b. It is challenging to explain this inner disk because most of the dust particles are expected to be trapped at the outer edge of the gap opened by b and c. By performing dust evolution models in combination with radiative transfer simulations that match the gas disk masses obtained from recent thermo-chemical models of we find that when the minimum grain size in the models is larger than 0.1mu m, there is an efficient filtration of dust particles, and the inner disk is depleted during the first million year of dust evolution. To maintain an inner disk, the minimum grain size in the models therefore needs to be smaller than 0.1mu m. Only when grains are that small are they diffused and dragged along with the gas throughout the gap opened by the planets. The small grains transported in the inner disk grow and drift into it, but the constant reservoir of dust particles that are trapped at the outer edge of the gap and that continuously fragment allows the inner disk to refill on million-year timescales. Our flux predictions at millimeter wavelength of these models agree with ALMA observations. These models predict a spectral index of 3.2 in the outer and 3.6 in the inner disk. Our simple analytical calculations show that the water emission in the inner disk that was recently observed with the James Webb Space Telescope may originate from these ice-coated small grains that flow through the gap, grow, and drift toward the innermost disk regions to reach the water snowline. These models may mirror the history and evolution of our Solar System, in which Jupiter and Saturn played a crucial role in shaping the architecture and properties of the planets.

Formation and structure of circumplanetary disks and envelopes during the late stages of giant planet formation

Giant planets are expected to form within circumstellar disks, which shape their formation history and the local environment. Here, we consider the formation and structure of circumplanetary disks that arise during the late stages of giant planet formation. During this phase, when most of the final mass is accumulated, incoming material enters the Hill sphere and falls toward the planet. In the absence of torques, the falling parcels of gas conserve their specific angular momentum and collect into a circumplanetary disk. Generalizing previous work, we consider a range of possible geometries for the flow entering the sphere of influence of the planet. Specifically, we consider five geometric patterns for the inward flow, ranging from concentration toward the rotational poles of the system to isotropic flow to concentration along the equatorial plane. For each case, we derive analytic descriptions for the density field of the infall region, the disk surface density in the absence of viscosity, and steady-state solutions for viscous disks. These results, in turn, specify the luminosity contributions of the planet, the circumplanetary disk, and the envelope. These power sources, in conjunction with the surrounding material, collectively determine the observational appearance of the forming planet. We conclude with an approximate determination of these radiative signatures.

A far-ultraviolet-driven photoevaporation flow observed in a protoplanetary disk.

Most low-mass stars form in stellar clusters that also contain massive stars, which are sources of far-ultraviolet (FUV) radiation. Theoretical models predict that this FUV radiation produces photodissociation regions (PDRs) on the surfaces of protoplanetary disks around low-mass stars, which affects planet formation within the disks. We report James Webb Space Telescope and Atacama Large Millimeter Array observations of a FUV-irradiated protoplanetary disk in the Orion Nebula. Emission lines are detected from the PDR; modeling their kinematics and excitation allowed us to constrain the physical conditions within the gas. We quantified the mass-loss rate induced by the FUV irradiation and found that it is sufficient to remove gas from the disk in less than a million years. This is rapid enough to affect giant planet formation in the disk.