Exoplanetary Systems Research Articles

There is no disk mass budget problem of planet formation

The inferred dust masses from Class II protoplanetary disk observations are lower than or equal to the masses of the observed exoplanet systems. This poses the question of how planets form if their natal environments do not contain enough mass. This hypothesis has entered the literature as the ``mass budget problem'' of planet formation. We utilized numerical simulations of planet formation via pebble and gas accretion, including migration, in a viscously evolving protoplanetary disk, while tracing the time evolution of the dust mass. As expected, we found that the presence of a giant planet in the disk can influence the evolution of the disk itself and prevent rapid dust mass loss by trapping the dust outside its orbit. Early formation is crucial for giant planet formation, as we found in our previous work; therefore, our findings strengthen the hypothesis that planet formation has already occurred or is ongoing in Class II disks. More importantly, we find that the optically thin dust mass significantly underestimates the total dust mass in the presence of a dust-trapping deep gap. We also show that the beam convolution smears out the feature from a deep gap, especially if the planet forms in the inner disk. Such hidden dust mass, along with early planet formation, could be the answer to the hypothetical mass budget problem.

The Mega-MUSCLES Treasury Survey: X-Ray to Infrared Spectral Energy Distributions of a Representative Sample of M Dwarfs

We present 5–1 × 107 Å spectral energy distributions (SEDs) for 12 M dwarf stars covering spectral types M0–M8. Our SEDs are provided for community use as a sequel to the Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems (MUSCLES) survey. The 12 stars include eight known exoplanet hosts and four stars chosen to fill out key parameter space in spectral type and rotation period. The SEDs are constructed from Hubble Space Telescope ultraviolet spectroscopy and XMM Newton, Chandra, and/or Swift X-ray observations, and completed with various model data, including Lyα reconstructions, PHOENIX optical models, APEC coronal models, and differential emission measure models in the currently-unobservable extreme ultraviolet. We provide a complete overview of the Mega-MUSCLES program, including a description of the observations, models, and SED construction. The SEDs are available as MAST high-level science products and we describe the various data products here. We also present ensemble measurements from our sample that are of particular relevance to exoplanet science, including the high-energy fluxes in the habitable zone and the far-ultraviolet to near-ultraviolet ratio. Combined with MUSCLES, Mega-MUSCLES provides SEDs covering a wide range of M dwarf spectral types and ages such that suitable proxies for any M dwarf planet host of interest may be found in our sample. However, we find that ultraviolet and X-ray fluxes can vary even between stars with similar parameters, such that observations of each exoplanet host star will remain the gold standard for interpreting exoplanet atmosphere observations.

More Likely Than You Think: Inclination-driving Secular Resonances Are Common in Known Exoplanet Systems

Multiplanet systems face significant challenges to detection. For example, farther-orbiting planets have a reduced signal-to-noise ratio in radial velocity detection methods, and small mutual inclinations between planets can prevent them from all transiting. One mechanism for exciting mutual inclination between planets is secular resonance, where the nodal precession frequencies of the planets align so as to greatly increase the efficiency of the angular momentum transport between planets. These resonances can significantly misalign planets from one another, hindering detection, and typically can only occur when there are three or more planets in the system. Naively, systems can only be in resonance for particular combinations of planet semimajor axes and masses; however, effects that alter the nodal precession frequencies of the planets, such as the decay of stellar oblateness, can significantly expand the region of parameter space where resonances occur. In this work, we explore known three-planet systems, determine whether they are in (or were in) secular resonance due to evolving stellar oblateness, and demonstrate the implications of resonance on their detectability and stability. We show that about 20% of a sample of three-planet transiting systems seem to undergo these resonances early in their lives.

A potential exomoon from the predicted planet obliquity of β Pictoris b

Planet obliquity is the alignment or misalignment of a planet spin axis relative to its orbit normal. In a multiplanet system, this obliquity is a valuable signature of planet formation and evolutionary history. The young β Pictoris system hosts two coplanar super-Jupiters and upcoming JWST observations of this system will constrain the obliquity of the outer planet, β Pictoris b. This will be the first planet obliquity measurement in an extrasolar, multiplanet system. First, we show that this new planet obliquity is likely misaligned by using a wide range of simulated observations in combination with published measurements of the system. Motivated by current explanations for the tilted planet obliquities in the Solar System, we consider collisions and secular spin-orbit resonances. While collisions are unlikely to occur, secular spin-orbit resonance modified by the presence of an exomoon around the outer planet can excite a large obliquity. The largest induced obliquities ( ∼60∘) occur for moons with at least a Neptune-mass and a semimajor axis of 0.03−0.05au ( 40−70 planet radii). For certain orbital alignments, such a moon may observably transit the planet (transit depth of 3−7%, orbital period of 3−7 weeks). Thus, a nonzero obliquity detection of β Pictoris b implies that it may host a large exomoon. Although we focus on the β Pictoris system, the idea that the presence of exomoons can excite high obliquities is very general and applicable to other exoplanetary systems.

The 10 pc Neighborhood of Habitable Zone Exoplanetary Systems: Threat Assessment from Stellar Encounters and Supernovae

The habitability of a planet is influenced by both its parent star and the properties of its local stellar neighborhood. Potential threats to habitability from the local stellar environment mainly arise from two factors: cataclysmic events such as powerful stellar explosions and orbital perturbations induced by close stellar encounters. Among the 4500+ exoplanet-hosting stars, about 140+ are known to host planets in their habitable zones (HZs). In this study, we use Gaia Data Release 3 data to investigate the 10 pc stellar neighborhood of the 84 habitable zone systems (HZSs) closest to the Sun. We assess the possible risks that the local stellar environments of these HZSs pose to their habitability. In particular, we find that HD 165155 has a high stellar density around it, making it likely to experience at least one flyby encounter within a span of 5 Gyr. We also identified two high-mass stars (M ≥ 8 M ⊙) as potential progenitors of supernovae, which could threaten the long-term survivability of HZSs HD 48265 and TOI-1227. Further, to quantify the similarity between HZ stars and the Sun, as well as their respective 10 pc stellar environments, we employ various astrophysical parameters to define a solar similarity index and a neighborhood similarity index. Our analysis suggests that HD 40307 exhibits the closest resemblance to the solar system, while HD 165155 shows the least resemblance.

Dust mass in protoplanetary disks with porous dust opacities

Atacama Large Millimeter/submillimeter Array surveys have suggested that protoplanetary disks are not massive enough to form the known exoplanet population, based on the assumption that the millimeter continuum emission is optically thin. In this work, we investigate how the mass determination is influenced when the porosity of dust grains is considered in radiative transfer models. The results show that disks with porous dust opacities yield similar dust temperatures, but systematically lower millimeter fluxes, as compared to disks that incorporate compact dust grains. Moreover, we have recalibrated the relation between dust temperature and stellar luminosity for a wide range of stellar parameters. We also calculated the dust masses of a large sample of disks using the traditionally analytic approach. The median dust mass from our calculation is about six times higher than the literature result, and this is mostly driven by the different opacities of porous and compact grains. A comparison of the cumulative distribution function between disk dust masses and exoplanet masses shows that the median exoplanet mass is about two times lower than the median dust mass when grains are assumed to be porous and there are no exoplanetary systems with masses higher than the most massive disks. Our analysis suggests that adopting porous dust opacities may alleviate the mass budget problem for planet formation. As an example illustrating the combined effects of optical depth and porous dust opacities on the mass estimation, we conducted new IRAM/NIKA-2 observations toward the IRAS 04370+2559 disk and performed a detailed radiative transfer modeling of the spectral energy distribution (SED). The best-fit dust mass is roughly 100 times higher than the value given by a traditionally analytic calculation. Future spatially resolved observations at various wavelengths are required to better constrain the dust mass.

The GAPS programme at TNG

Context. Atmospheric characterisation plays a key role in the study of exoplanetary systems, giving hints about the current and past conditions of the planets. The information retrieved from the analysis of pivotal lines such as the Hα and He I triplet allow us to constrain the evolutionary path of the planets due to atmospheric photo-evaporation. After focussing for many years on ultra-hot Jupiters, atmospheric characterisation is slowly moving towards smaller and colder planets, which are harder to study due to the difficulties in extracting the planetary signal and which require more precise analysis. Aims. We aim to characterise the atmosphere of TOI-5398 b (P ~ 10.59 days), the outer warm Saturn orbiting a young (~650 Myr) G-type star that also hosts the small inner planet TOI-5398 c (P ~ 4.77 days). Both planets are suitable for atmospheric probing due to the closeness to their host star, which results in strong photo-evaporation processes, especially the larger outer one with an estimated transmission spectroscopy metric of 288 (higher than those of several well-known hot Jupiters). Methods. We investigated the atmosphere of planet b, analysing the data collected during a transit with HARPS-N and GIANO-B high-resolution spectrographs, employing both cross-correlation and single-line analysis to study the presence of atomic species. Incidentally, we recorded the simultaneous transit of planet c, and hence we also focussed on discerning the origin of the signal. We expect planet b to be the cause of the detected signal, since, according to existing evaporation models, it is currently expected to lose more mass than planet c. Results. We detected the presence of Hα and He I triplets, two markers of the photo-evaporation processes predicted for the system, retrieving a height in the atmosphere of 2.33 Rp and 1.65 Rp, respectively. We confirmed these predictions by employing the models computed with the ATES software, which predict a He I absorption arising from planet b comparable with the observed one. Moreover, the ATES models suggested an He/H ratio of 1/99 to match our observations. The investigation of atomic species led to the detection of an Na I doublet via single-line analysis, while the cross-correlation did not return a detection for any of the atomic species investigated.

Study of the resonant motion of a test particle inside Kepler 69 using circular restricted three body problem

Summary: Scientific researches to discover extraterrestrial life are very intense and important. For a long time, humanity has speculated about the existence of the planetary systems different from our solar system, where extraterrestrial life can be existing elsewhere in the universe. The understanding of the origin of planets and planetary systems has indeed become a major focus of research in modern Astrophysics. Exoplanet research is one of the most field developing subjects in Astrophysics and Astronomy. Today, the number of discovered exoplanets, where life is thought to exist, is large. One of the main goals of scientists is to find Earth 2, where there is possibility of extraterrestrial life. Kepler's mission was, and is very important in the field of exoplanet research. This mission has revolutionized our understanding of exoplanets. The number of discovered exoplanets has exceeded 5780 in 4314 planetary systems, with 969 systems having more than one planet [1]. Among them, one of the most interesting is Kepler 69 c, a super-Earth around Kepler 69. This exoplanet is located at the boundary between the habitable zone and the outer one. In this study let’s focus on the classical gravitational problem called Circular Restricted Three-Body Problem (CRTBP) [2, 3] and use an iterative method to perform numerical calculations through MATLAB software. Therefore, in this paper, let’s try to study the movement of a “test particle”, under the action of the gravitational field of the system Kepler 69–Kepler 69 c. The aim of this paper is to study the motion of a “test particle” (for example an extrasolar asteroid test) inside the exoplanetary system Kepler 69. Results are presented in the (x, y) plane in the rotating and inertia system. Also, some of the results are presented in the phase planes (x, vx) and (y, vy)

Constraining the Presence of Companion Planets in Hot Jupiter Planetary Systems Using Transit-timing Variation Observations from TESS

The presence of another planetary companion in a transiting exoplanet system can impact its transit light curve, leading to sinusoidal transit-timing variations (TTV). By utilizing both χ 2 and rms analysis, we have combined the TESS observation data with an N-body simulation to investigate the existence of an additional planet in the system and put a limit on its mass. We have developed CMAT, an efficient and user-friendly tool for fitting transit light curves and calculating TTV with a theoretical period, based on which we can give a limit on its hidden companion’s mass. We use 260 hot Jupiter systems from the complete TESS data set to demonstrate the use of CMAT. Our findings indicate that, for most systems, the upper mass limit of a companion planet can be restricted to several Jupiter masses. This constraint becomes stronger near resonance orbits, such as the 1:2, 2:1, 3:1, and 4:1 mean-motion resonance, where the limit is reduced to several Earth masses. These findings align with previous studies suggesting that a lack of companion planets with resonance in hot Jupiter systems could potentially support the high-eccentricity migration theory. Additionally, we observed that the choice between χ 2 or rms method does not significantly affect the upper limit on companion mass; however, χ 2 analysis may result in weaker restrictions but is statistically more robust compared to rms analysis in most cases.

Migration of Celestial Bodies in the Solar System and in Some Exoplanetary Systems

Migration of Celestial Bodies in the Solar System and in Some Exoplanetary Systems

Development of Gravity Theories in the View of TRAPPIST-1e

Abstract Contrary to the solar system, most exoplanet systems detected hitherto are close-in and compact. One typical system is TRAPPIST-1, which has seven nearly co-planar terrestrial planets all within the orbit of Mercury, including three in the habitable zone.
To evaluate the differences in development of sophisticated gravity theories from the solar system, we use N-body integrations to simulate ephemeris and reproduce some important astronomy phenomena observed on the potentially habitable planet TRAPPIST-1e.
Retrograde motions of other planets last 1–2 orders of magnitude shorter than in the solar system, but occur much more frequently. Transit events of all inner planets can be observed steadily. 
Except Kepler's first law is hard to notice for low eccentricities of planets, the other two laws can then be precisely verified in 102 days, because the areas swept by planets vary by <~ 0.01% and the observed semimajor axes and periods result in constants with theoretical and observation accuracies both <~ 2%. However, the mean motion correlation implies the Great Inequality does not keep apparent between one pair of planets like Jupiter and Saturn.
Furthermore, general relativity can hardly be discovered because it gives rise to perihelion precession of inner planets only ∼0.1% of gravity precession, dozens of times smaller than Mercury. 
Our results supports the possibility of developing part of gravity theories by potential exo-civilizations in compact systems like TRAPPIST-1.

How might a planet between Mars and Jupiter influence the inner solar system? effects on orbital motion, obliquity, and eccentricity

As implied by exoplanet population censuses, super-Earths are extremely common in the galaxy. In the solar system, models suggest that the formation of an Earth-to-super-Earth mass planet could have readily occurred in the inner regions (<3 AU) if such body is able to survive the early intense and chaotic intertaction episodes of the Jovian worlds with the rest of the solar system. In this study, we test the consequences of such a hypothesis using a three-dimensional (3D) N-Rigid-Body integrator. With a 3D model in which the planet is modeled as a rigid body to account for its finite size and rotation, we simulate the orbital evolution of the three inner terrestrial planets over 2 Myr periods. Our results show that an additional super-Earth sized planet between 2 and 3.5 AU would have (i) destabilized Earth’s orbit over timescales of 1-2 Myrs, (ii) increased Mars’s obliquity by ∼55°, and (iii) perturbed the eccentricity of Venus by up to e∼0.4. Our study explores an “alternate fate” of the terrestrial planets and our results suggest that the formation of a super-Earth in the inner solar system would have exerted grave consequences for the orbital dynamics and habitability of the terrestrial planets.

Self-consistent N-body simulation of planetesimal-driven migration. I. The trajectories of single planets in the uniform background

Abstract Recent exoplanet observations have revealed a diversity of exoplanetary systems, which suggests the ubiquity of radial planetary migration. One powerful known mechanism of planetary migration is planetesimal-driven migration (PDM), which can let planets undergo significant migration through gravitational scattering with planetesimals. In this series of papers, we present the results of our high-resolution, self-consistent N-body simulations of PDM, in which gravitational interactions among planetesimals, the gas drag, and Type I migration are all taken into account. In this first paper (Paper I), we investigate the migration of a single planet through PDM within the framework of the classical standard disk model (the minimum-mass solar nebula model). Paper I aims to improve our understanding of planetary migration through PDM, addressing previously unexplored aspects of both the gravitational interactions among planetesimals and the interactions with disk gas. Our results show that even small protoplanets can actively migrate through PDM. Such active migration can act as a rapid radial diffusion mechanism for protoplanets and significantly influence the early stages of planetary formation (i.e., during the runaway growth phase). Moreover, a fair fraction of planets migrate outward. This outward migration may offer a potential solution for the “planet migration problem” caused by Type I migration and gives a natural mechanism for outward migration assumed in many recent scenarios for the formation of outer planets.

Neural-Rendezvous: Provably Robust Guidance and Control to Encounter Interstellar Objects

Interstellar objects (ISOs) are likely representatives of primitive materials invaluable in understanding exoplanetary star systems. Due to their poorly constrained orbits with generally high inclinations and relative velocities, however, exploring ISOs with conventional human-in-the-loop approaches is significantly challenging. This paper presents Neural-Rendezvous—a deep-learning-based guidance and control framework for encountering fast-moving objects, including ISOs, robustly, accurately, and autonomously in real time. It uses pointwise minimum norm tracking control on top of a guidance policy modeled by a spectrally normalized deep neural network, where its hyperparameters are tuned with a loss function directly penalizing the model predictive control state trajectory tracking error. We show that Neural-Rendezvous provides a high probability exponential bound on the expected spacecraft delivery error, the proof of which leverages stochastic incremental stability analysis. In particular, it is used to construct a non-negative function with a supermartingale property, explicitly accounting for the ISO state uncertainty and the local nature of nonlinear state estimation guarantees. In numerical simulations, Neural-Rendezvous is demonstrated to satisfy the expected error bound for 100 ISO candidates. This performance is also empirically validated using our spacecraft simulator and in high-conflict and distributed unmanned aerial vehicle swarm reconfiguration with up to 20 unmanned aerial vehicles.

Modified method of round Gaussian rings. Application to the two-planetary problem

A scheme of the modified method of round Gaussian rings, designed to study the secular evolution of orbits in systems consisting of a central star and two planets, is presented. The reason for the secular evolution of the nodes and inclinations of the orbits of the planets is their mutual gravitational attraction. The orbits of the planets are modeled by homogeneous round Gaussian rings, to which the masses, sizes and angles of inclination of the orbits, as well as orbital angular momenta of the planets, are transferred. The method takes into account the fact that, in general, the ascending nodes of the orbits may not coincide. The mutual gravitational energy of the rings 𝑊𝑚𝑢𝑡 is represented as a series in the quadratic approximation in powers of small inclination angles. Using this function 𝑊𝑚𝑢𝑡, a closed system of four differential equations describing the secular evolution of the planets’ orbits is composed. The solution to the equations is obtained in finite analytic form, which simplifies the interpretation of the investigated planetary motions. The method was tested on the example of the Sun-Jupiter-Saturn system; for it, in particular, the difference in the longitudes of the nodes of the orbits of Jupiter and Saturn was calculated as a function of time. New approach is also used to study the precession of nodes in the exoplanetary system K2-36; graphs of all unknown quantities are obtained. It has been established that in the course of evolution the mutual inclination angle of the orbits remains constant, and the librations of the orbits in the inclination angle and in the motion of the nodes occur synchronously.

The HD 191939 Exoplanet System is Well Aligned and Flat

We report the sky-projected spin–orbit angle λ for HD 191939 b, the innermost planet in a six-planet system, using Keck/KPF to detect the Rossiter–McLaughlin (RM) effect. Planet b is a sub-Neptune with radius 3.4 ± 0.8 R ⊕ and mass 10.0 ± 0.7 M ⊕ with an RM amplitude <1 m s−1. We find the planet is consistent with a well-aligned orbit, measuring λ = 3.°7 ± 5.°0. Additionally, we place new constraints on the mass and period of the distant super-Jupiter, planet f, finding it to be 2.88 ± 0.26 M J on a 2898 ± 152 days orbit. With these new orbital parameters, we perform a dynamical analysis of the system and constrain the mutual inclination of the nontransiting planet e to be smaller than 12° relative to the plane shared by the inner three transiting planets. Additionally, the further planet f is inclined off this shared plane, the greater the amplitude of precession for the entire inner system, making it increasingly unlikely to measure an aligned orbit for planet b. Through this analysis, we show that this system’s wide variety of planets are all well-aligned with the star and nearly coplanar, suggesting that the system formed dynamically cold and flat out of a well-aligned protoplanetary disk, similar to our own solar system.

Stochastic excitation of waves in magnetic stars

Context. Stellar oscillations are key to unravelling stellar properties, such as their mass, radius, and age. This in turn enables us to date and characterize their exoplanetary systems. The amplitudes of acoustic (p-) modes in solar-like stars are intrinsically linked to their convective turbulent excitation source, which in turn is influenced by magnetism. In the observations of the Sun and stars, the mode amplitudes are modulated following their magnetic activity cycles: the higher the magnetic field, the lower the mode amplitudes. When the magnetic field is strong, it can even inhibit acoustic modes, which are not detected in most of the solar-like stars that are strongly magnetically active. Magnetic fields are known to freeze convection when they stronger than a critical value: the so-called on-off approach is used in the literature. Aims. We investigate the impact of magnetic fields on the stochastic excitation of acoustic modes. Methods. First, we generalise the forced-wave equation formalism, including the effects of magnetic fields. Second, we assess how convection is affected by magnetic fields using results from the magnetic mixing-length theory. Results. We provide the source terms of the stochastic excitation, including a new magnetic source term and the Reynolds stresses. We derive scaling laws for the mode amplitudes that take both the driving and the damping into account. These scalings are based on the inverse Alfvén dimensionless parameter: The damping increases with the magnetic field and reaches a saturation threshold when the magnetic field is strong. The driving of the modes diminishes when the magnetic field becomes stronger and the turbulent convection is weaker. Conculsions. As expected from the observations, we find that a stronger magnetic field diminishes the resulting mode amplitudes. The evaluation of the inverse Alfvén number in stellar models provides a means for estimating the expected amplitudes of acoustic modes in magnetically active solar-type stars.

SETI at FAST in China

Abstract Since the commencement of the first SETI observation in 2019, China’s Search for Extraterrestrial Intelligence program has garnered momentum through domestic support and international collaborations. Several observations targeting exoplanets and nearby stars have been conducted with the Five-hundred-metre Aperture Spherical Telescope (FAST). In 2023 the introduction of the Far Neighbour Project (FNP) marked a substantial leap forward, driven by the remarkable sensitivity of the FAST telescope and some of the novel observational techniques. The FNP seeks to methodically detect technosignatures from celestial bodies, including nearby stars, exoplanetary systems, Milky Way globular clusters and more. This paper provides an overview of the progress achieved by SETI in China and offers insights into the distinct phases comprising the FNP. Additionally it underscores the significance of this project’s advancement and its potential contributions to the field.

Unveiling the HD 95086 system at mid-infrared wavelengths with JWST/MIRI

Context. Mid-infrared imaging of exoplanets and disks is now possible with the coronographs of the Mid-InfraRed Instrument (MIRI) on the James Webb Space Telescope (JWST). This wavelength range unveils new features of young directly imaged systems and allows us to obtain new constraints for characterizing the atmosphere of young giant exoplanets and associated disks. Aims. These observations aim to characterize the atmosphere of the planet HD 95086 b by adding mid-infrared information so that the various hypotheses about its atmospheric parameters values can be unraveled. Improved images of cirsumstellar disks are provided. Methods. We present the MIRI coronagraphic imaging of the system HD 95086 obtained with the F1065C, F1140, and F2300C filters at central wavelengths of 10.575 µm, 11.3 µm, and 23 µm, respectively. We explored the method for subtracting the stellar diffraction pattern in the particular case when bright dust emitting at short separation is present. Furthermore, we compared different methods for extracting the photometry of the planet. Using the atmospheric models Exo-REM and ATMO, we measured the atmospheric parameters of HD 95086 b. Results. The planet HD 95086 b is detected at the two shortest MIRI wavelengths F1065C and F1140C. The contribution from the inner disk of the system is also detected. It is similar to that in the HR 8799 system. The outer colder belt is imaged at 23 µm. Background objects are observed in all filters. The mid-infrared photometry provides better constraints on the atmospheric parameters. We evaluate a temperature of 800–1050 K, consistent with one previous hypothesis that only used near-infrared data. The radius measurement of 1.0–1.14 RJup is better aligned with evolutionary models, but still smaller than predicted. These observations allow us to refute the hypothesis of a warm circumplanetary disk. Conclusions. HD 95086 is one of the first exoplanetary systems to be revealed at mid-infrared wavelengths. This highlights the interests and challenges of observations at these wavelengths.

The Wanderer: Charting WASP-77A b’s Formation and Migration Using a System-wide Inventory of Carbon and Oxygen Abundances

The elemental and isotopic abundances of volatiles like carbon, oxygen, and nitrogen may trace a planet’s formation location relative to H2O, CO2, CO, NH3, and N2 “snowlines,” or the distance from the star at which these volatile elements sublimate. By comparing the C/O and 12C/13C ratios measured in giant exoplanet atmospheres to complementary measurements of their host stars, we can determine whether the planet inherited stellar abundances from formation inside the volatile snowlines, or nonstellar C/O and 13C enrichment characteristic of formation beyond the snowlines. To date, there are still only a handful of exoplanet systems where we can make a direct comparison of elemental and isotopic CNO abundances between an exoplanet and its host star. Here, we present a 12C/13C abundance analysis for host star WASP-77A (whose hot Jupiter’s 12C/13C abundance was recently measured). We use MARCS stellar atmosphere models and the radiative transfer code TurboSpectrum to generate synthetic stellar spectra for isotopic abundance calculations. We find a 12C/13C ratio of 51 ± 6 for WASP-77A, which is subsolar (∼91) but may still indicate 13C enrichment in its companion planet WASP-77A b (12C/13C = 26 ± 16, previously reported). Together with the inventory of carbon and oxygen abundances in both the host and companion planet, these chemical constraints point to WASP-77A b’s formation beyond the H2O and CO2 snowlines and provide chemical evidence for the planet’s migration to its current location ∼0.024 au from its host star.