Planetary Mass Research Articles

Into the Mystic: the MUSE view of the ionized gas in the Mystic Mountains in Carina

Abstract We present optical integral field unit (IFU) observations of the Mystic Mountains, a dust pillar complex in the center of the Carina Nebula that is heavily irradiated by the nearby young massive cluster Trumpler 14. With the continuous spatial and spectral coverage of data from the Multi-Unit Spectroscopic Explorer (MUSE), we measure the physical properties in the ionized gas including the electron density and temperature, excitation, and ionization. MUSE also provides an excellent view of the famous jets HH 901, 902, and 1066, revealing them to be high-density, low-ionization outflows despite the harsh environment. HH 901 shows spatially extended [C i] emission tracing the rapid dissociation of the photoevaporating molecular outflow in this highly irradiated source. We compute the photoevaporation rate of the Mystic Mountains and combine it with recent ALMA observations of the cold molecular gas to estimate the remaining lifetime of the Mystic Mountains and the corresponding shielding time for the embedded protostars. The longest remaining lifetimes are for the smallest structures, suggesting that they have been compressed by ionizing feedback. Our data do not suggest that star formation in the Mystic Mountains has been triggered but it does point to the role that ionization-driven compression may play in enhancing the shielding of embedded stars and disks. Planet formation models suggest that the shielding time is a strong determinant of the mass and orbital architecture of planets, making it important to quantify in high-mass regions like Carina that represent the type of environment where most stars form.

Gaia-4b and 5b: Radial Velocity Confirmation of Gaia Astrometric Orbital Solutions Reveal a Massive Planet and a Brown Dwarf Orbiting Low-mass Stars

Abstract Gaia astrometry of nearby stars is precise enough to detect the tiny displacements induced by substellar companions, but radial velocity (RV) data are needed for definitive confirmation. Here we present RV follow-up observations of 28 M and K stars with candidate astrometric substellar companions, which led to the confirmation of two systems, Gaia-4b and Gaia-5b, identification of five systems that are single lined but require additional data to confirm as substellar companions, and the refutation of 21 systems as stellar binaries. Gaia-4b is a massive planet (M = 11.8 ± 0.7 M J) in a P = 571.3 ± 1.4 day orbit with a projected semimajor axis a 0 = 0.312 ± 0.040 mas orbiting a 0.644 ± 0.02M ⊙ star. Gaia-5b is a brown dwarf (M = 20.9 ± 0.5M J) in a P = 358.62 ± 0.20 days eccentric e = 0.6423 ± 0.0026 orbit with a projected angular semimajor axis of a 0 = 0.947 ± 0.038 mas around a 0.34 ± 0.03M ⊙ star. Gaia-4b is one of the first exoplanets discovered via the astrometric technique, and is one of the most massive planets known to orbit a low-mass star.

2-D numerical experiments of thermal convection of highly viscous fluids under strong adiabatic compression: implications on mantle convection of super-Earths with various sizes

We conduct a series of numerical experiments of thermal convection of compressible fluids with temperature-dependent viscosity, in order to study how the adiabatic compression and model geometries affect the mantle convection on super-Earths. A two-dimensional basally heated convection is considered under the truncated anelastic liquid approximation (TALA), either in a rectangular box or in a cylindrical annulus. We varied the magnitude of adiabatic heating and the Rayleigh number as well as the depth profile of thermodynamic properties (thermal expansivity and reference density) in accordance with the planetary sizes. From our calculations by varying the planetary sizes up to 10 times the Earth’s mass, we confirmed that the adiabatic compression affects the thermal convection more strongly for larger planets. The activity of hot plumes originating from the core–mantle boundary is significantly suppressed in the terrestrial planets whose mass is larger than the Earth’s by a factor of about 3 regardless of the model geometries. We also developed scaling relationships between the vigor of thermal convection and the planetary mass by appropriately incorporating the effect of adiabatic compression into those of Boussinesq (or incompressible) cases. Our scaling relationships suggest that the stress level in the top cold thermal boundary layers is almost independent of the planetary mass, which may further imply that the emergence of plate tectonics is not likely to be enhanced for massive terrestrial planets whose composition is similar to the Earth’s.Graphical

Stellar X-Ray Variability and Planetary Evolution in the DS Tucanae System

Abstract We present an analysis of four Chandra observations of the 45 Myr old DS Tuc binary system. We observed X-ray variability of both stars on timescales from hours to months, including two strong X-ray flares from star A. The implied flaring rates are in agreement with past observations made with XMM-Newton, though these rates remain imprecise due to the relatively short total observation time. We find a clear, monotonic decline in the quiescent level of the star by a factor of 1.8 across 8 months, suggesting stellar variability that might be due to an activity cycle. If proven through future observations, DS Tuc A would be the youngest star for which a coronal activity cycle has been confirmed. The variation in our flux measurements across the four visits is also consistent with the scatter in empirical stellar X-ray relationships with Rossby number. In simulations of the possible evolution of the currently super-Neptune-sized planet DS Tuc A b, we find a range of scenarios for the planet once it reaches a typical field age of 5 Gyr, from Neptune size down to a completely stripped super-Earth. Improved constraints on the planet's mass in the future would significantly narrow these possibilities. We advocate for further Chandra observations to better constrain the variability of this important system.

Revised Masses for Low-density Planets Orbiting the Disordered M-dwarf System TOI-1266

Abstract We present an analysis of 126 new radial velocity measurements from the MAROON-X spectrograph to investigate the TOI-1266 system, which hosts two known transiting sub-Neptunes at 10.8 and 18.8 days. We integrated our measurements with existing HARPS-N measurements for this system and derived revised masses for TOI-1266 b and c of M b = 4.09 ± 0.45M ⊕ and M c = 2.64 ± 0.52M ⊕, respectively. The Keplerian fit from the combined datasets enabled an ≈35% and ≈41% improvement in mass precision for planet b and c, respectively, compared to the previously published values. With bulk densities of ρ b = 1.25 ± 0.21 g cm−3 and ρ c = 1.51 ± 0.39 g cm−3, the planets are among the lowest density sub-Neptunes orbiting an M dwarf. They are both consistent with rocky cores surrounded by hydrogen helium envelopes. TOI-1266 c may also be consistent with a water-rich composition, but we disfavor that interpretation from an Occam's razor perspective.

KOBE-1: The first planetary system from the KOBE survey

Context. K-dwarf stars are promising targets in the exploration of potentially habitable planets. Their properties, falling between G and M dwarfs, provide an optimal trade-off between the prospect of habitability and ease of detection. The KOBE experiment is a blind-search survey exploiting this niche, monitoring the radial velocity of 50 late-type K-dwarf stars. It employs the CARMENES spectrograph, with an observational strategy designed to detect planets in the habitable zone of their system. Aims. In this work, we exploit the KOBE data set to characterize planetary signals in the K7 V star HIP 5957 (KOBE-1) and to constrain the planetary population within its habitable zone. Methods. We used 82 CARMENES spectra over a time span of three years. We employed a generalized Lomb–Scargle periodogram to search for significant periodic signals that would be compatible with Keplerian motion on KOBE-1. We carried out a model comparison within a Bayesian framework to ensure the significance of the planetary model over alternative configurations of lower complexity. We also inspected two available TESS sectors in search of planetary signals. Results. We identified two signals: at Pb = 8.5 d and Pc = 29.7 d. We confirmed their planetary nature through ruling out other non-planetary configurations. Their minimum masses are 8.80 ± 0.76 M⊕ (KOBE-1 b), and 12.4 ± 1.1 M⊕ (KOBE-1 c), corresponding to absolute masses within the planetary regime at a high certainty (>99.7%). By analyzing the sensitivity of the CARMENES time series to additional signals, we discarded planets above 8.5 M⊕ within the habitable zone. We identified a single transit-like feature in TESS, whose origin is still uncertain, but still compatible within 1σ with a transit from planet c. Conclusions. The KOBE-1 multi-planetary system, consisting of a relatively quiet K7-dwarf hosting two sub-Neptune-minimum- mass planets, establishes the first discovery from the KOBE experiment. We have explored future prospects for characterizing this system, concluding that Gaia DR4 will be insensitive to their astrometric signature. Meanwhile, nulling interferometry with the Large Interferometer For Exoplanets (LIFE) mission could be capable of directly imaging both planets and characterizing their atmospheres in future studies.

Planetesimal formation in a pressure bump induced by infall

Infall of interstellar material is a potential non-planetary origin of pressure bumps in protoplanetary disks. While pressure bumps arising from other mechanisms have been numerically demonstrated to promote planet formation, the impact of infall-induced pressure bumps remains unexplored. We aim to investigate the potential for planetesimal formation in an infall-induced pressure bump, starting with sub-micrometer-sized dust grains, and to identify the conditions most conducive to triggering this process. We developed a numerical model that integrates axisymmetric infall, dust drift, and dust coagulation, along with planetesimal formation via streaming instability. Our parameter space includes gas viscosity, dust fragmentation velocity, initial disk mass, characteristic disk radius, infall rate and duration, as well as the location and width of the infall region. An infall-induced pressure bump can trap dust from both the infalling material and the outer disk, promoting dust growth. The locally enhanced dust-to-gas ratio triggers streaming instability, forming a planetesimal belt inside the central infall location until the pressure bump is smoothed out by viscous gas diffusion. Planetesimal formation is favored by a massive, narrow streamer infalling onto a low-viscosity, low-mass, and spatially extended disk containing dust with a high fragmentation velocity. This configuration enhances the outward drift speed of dust on the inner side of the pressure bump, while also ensuring the prolonged persistence of the pressure bump. Planetesimal formation can occur even if the infalling material consists solely of gas. A pressure bump induced by infall is a favorable site for dust growth and planetesimal formation, and this mechanism does not require a preexisting massive planet to create the bump.

The NCORES Program: Precise planetary masses, null results, and insight into the planet mass distribution near the radius gap

Abstract NCORES was a large observing program on the ESO HARPS spectrograph, dedicated to measuring the masses of Neptune-like and smaller transiting planets discovered by the TESS satellite using the radial velocity technique. This paper presents an overview of the programme, its scientific goals and published results, covering 35 planets in 18 planetary systems. We present spectrally derived stellar characterisation and mass constraints for five additional TOIs where radial velocity observations found only marginally significant signals (TOI-510.01, $M_p = 1.08^{+0.58}_{-0.55}M_{\hbox{$\oplus $}}$), or found no signal (TOIs 271.01, 641.01, 697.01 and 745.01). A newly detected non-transiting radial velocity candidate is presented orbiting TOI-510 on a 10.0d orbit, with a minimum mass of $4.82^{+1.29}_{-1.26}M_{\hbox{$\oplus $}}$, although uncertainties on the system architecture and true orbital period remain. Combining the NCORES sample with archival known planets we investigate the distribution of planet masses and compositions around and below the radius gap, finding that the population of planets below the gap is consistent with a rocky composition and ranges up to a sharp cut-off at 10M⊕. We compare the observed distribution to models of pebble- and planetesimal-driven formation and evolution, finding good broad agreement with both models while highlighting interesting areas of potential discrepancy. Increased numbers of precisely measured planet masses in this parameter space are required to distinguish between pebble and planetesimal accretion.

Effects of Planetary Mass Uncertainties on the Interpretation of the Reflectance Spectra of Earth-like Exoplanets

Abstract Atmospheric characterization of Earth-like exoplanets through reflected light spectroscopy is a key goal for upcoming direct imaging missions. A critical challenge in this endeavor is the accurate determination of planetary mass, which may influence the measurement of atmospheric compositions and the identification of potential biosignatures. In this study, we used the Bayesian retrieval framework EXOREL ℜ to investigate the impact of planetary mass uncertainties on the atmospheric characterization of terrestrial exoplanets observed in reflected light. Our results indicate that precise prior knowledge of the planetary mass can be crucial for accurate atmospheric retrievals if clouds are present in the atmosphere. When the planetary mass is known within 10% uncertainty, our retrievals successfully identified the background atmospheric gas and accurately constrained atmospheric parameters together with clouds. However, with less constrained or unknown planetary mass, we observed significant biases, particularly in the misidentification of the dominant atmospheric gas. For instance, the dominant gas was incorrectly identified as oxygen for a modern Earthlike planet or carbon dioxide for an Archean Earth–like planet, potentially leading to erroneous assessments of planetary habitability and biosignatures. These biases arise because the uncertainties in planetary mass affect the determination of surface gravity and atmospheric scale height, leading the retrieval algorithm to compensate by adjusting the atmospheric composition. Our findings emphasize the importance of achieving precise mass measurements—ideally within 10% uncertainty—through methods such as extreme precision radial velocity or astrometry, especially for future missions like the Habitable Worlds Observatory.

Two almost planetary mass survivors of common envelope evolution

Abstract White dwarfs are often found in close binaries with stellar or even substellar companions. It is generally thought that these compact binaries form via common envelope evolution, triggered by the progenitor of the white dwarf expanding after it evolved off the main-sequence and engulfing its companion. To date, a handful of white dwarfs in compact binaries with substellar companions have been found, typically with masses greater than around 50 MJup. Here we report the discovery of two eclipsing white dwarf plus brown dwarf binaries containing very low mass brown dwarfs. ZTF J1828+2308 consists of a hot (15900 ± 75 K) 0.610 ± 0.004 M⊙ white dwarf in a 2.7 hour binary with a 0.0186 ± 0.0008 M⊙ (19.5 ± 0.8 MJup) brown dwarf. ZTF J1230−2655 contains a cool (10000 ± 110 K) 0.65 ± 0.02 M⊙ white dwarf in a 5.7 hour binary with a companion that has a mass of less than 0.0211 M⊙ (22.1 MJup). While the brown dwarf in ZTF J1828+2308 has a radius consistent with its mass and age, ZTF J1230−2655 contains a roughly 20 per cent overinflated brown dwarf for its age. We are only able to reconstruct the common envelope phase for either system if it occurred after the first thermal pulse, when the white dwarf progenitor had already lost a significant fraction of its original mass. This is true even for very high common envelope ejection efficiencies (αCE ∼ 1), unless both systems have extremely low metallicities. It may be that the lowest mass companions can only survive a common envelope phase if it occurs at this very late stage.

Characterising WASP-43b's interior structure: Unveiling tidal decay and apsidal motion

Recent developments in exoplanetary research highlight the importance of Love numbers in understanding the internal dynamics, formation, migration history, and potential habitability of exoplanets. Love numbers represent crucial parameters that gauge how exoplanets respond to external forces such as tidal interactions and rotational effects. By measuring these responses, insights into the internal structure, composition, and density distribution of exoplanets can be gained. The rate of apsidal precession of a planetary orbit is directly linked to the second-order fluid Love numbers. Thus, Love numbers can also offer valuable insights into the mass distribution of a planet. In this context, we aim to re-determine the orbital parameters of WASP-43b - in particular, the orbital period, eccentricity, and argument of the periastron - and its orbital evolution. We study the outcomes of the tidal interaction with the host star in order to identify whether tidal decay and periastron precession occur in the system. We observed WASP-43b with HARPS, whose data we present for the first time, and we also analysed the newly acquired JWST full-phase light curve. We jointly fit new and archival radial velocity and transit and occultation mid-times, including tidal decay, periastron precession, and long-term acceleration in the system. We detected a tidal decay rate of dot P _a= (-1.99±0.50) ms yr^-1 and a periastron precession rate of )^∘ d^-1 = (621.72 ^ This is the first time that both periastron precession and tidal decay are simultaneously detected in an exoplanetary system. The observed tidal interactions can neither be explained by the tidal contribution to apsidal motion of a non-aligned stellar or planetary rotation axis nor by assuming a non-synchronous rotation for the planet, and a value for the planetary Love number cannot be derived. Moreover, we excluded the presence of a second body (e.g. a distant companion star or a yet undiscovered planet) down to a planetary mass of ≳0.3 M_J and up to an orbital period of lesssim 3,700 days. We leave the question of the cause of the observed apsidal motion open.

True Mass and Atmospheric Composition of the Nontransiting Hot Jupiter HD 143105 b

Abstract We present Keck/KPIC Phase II K-band observations of the nontransiting hot Jupiter HD 143105 b. Using a cross-correlation approach, we make the first detection of the planetary atmosphere at K p = 18 5 − 13 + 11 km s−1 and an inferior conjunction time 2.5 hr before the previously published ephemeris. The retrieved K p value, in combination with the orbital period, mass of the host star, and lack of transit detection, give an orbital inclination of 7 8 − 12 ∘ + 2 and a true planet mass of 1.23 ± 0.10 M J. While the equilibrium temperature of HD 143105 b is in the transition regime between noninverted and inverted atmospheres, our analysis strongly prefers a noninverted atmosphere. Retrieval analysis indicates the atmosphere of HD 143105 b is cloud free to approximately 1 bar and dominated by H2O absorption ( logH 2 O MMR = − 3 . 9 − 0.5 + 0.8 ), placing only an upper limit on the CO abundance ( logCO MMR < − 3.7 at 95% confidence). We place no constraints on the abundances of Fe, Mg, or 13CO. From these abundances, we place an upper limit on the carbon-to-oxygen ratio for HD 143105 b, C/O < 0.2 at 95% confidence, and find the atmospheric metallicity is approximately 0.1 × solar. The low metallicity may be responsible for the lack of a thermal inversion, which at the temperature of HD 143105 b would likely require significant opacity from TiO and/or VO. With these results, HD 143105 b joins the small number of nontransiting hot Jupiters with detected atmospheres.

Analyses of Multiple Balmer Emission Lines from Accreting Brown Dwarfs and Very Low Mass Stars

Abstract A planetary growth rate, i.e., the mass accretion rate, is a fundamental parameter in planet formation, as it determines a planet's final mass. Planetary mass accretion rates have been estimated using hydrogen lines, based on the models originally developed for accreting stars, known as the accretion flow model. Recently, Aoyama et al. introduced the accretion shock model as an alternative mechanism for hydrogen line emission. However, it remains unclear which model is more appropriate for accreting planets and substellar objects. To address this, we applied both models to archival data consisting of 96 data points from 76 accreting brown dwarfs and very-low-mass stars, with masses ranging from approximately 0.02 to 0.1 M ⊙, to test which model best explains their accreting properties. The results showed that the emission mechanisms of 15 data points are best explained by the shock model, while 55 data points are best explained by the flow model. For the 15 data points explained by the planetary shock model, the shock model estimates up to several times higher mass accretion rates than the flow model. As this trend is more pronounced for planetary-mass objects, it is crucial to determine which emission mechanism is dominant in individual planets. We also discuss the physical parameters that determine the emission mechanisms and the variability of line ratios.

Planetary Mass Determinations from a Simplified Photodynamical Model—Application to the Complete Kepler Dataset

We use PyDynamicaLC, a model using the least number of—and the least correlated—degrees of freedom needed to derive a photodynamical model, to describe some of the smallest—and lowest-transit-timing-variation-amplitude—of the Kepler planets. We successfully analyze 64 systems containing 218 planets, for 88 of which we were able to determine significant masses (to better than 3σ). We demonstrate consistency with literature results over 2 orders of magnitude in mass, and for the planets that already had literature mass estimations, we were able to reduce the relative mass error by ∼22% (median value). Of the planets with determined masses, 23 are new mass determinations, with no previous significant literature values, including a planet smaller and lighter than Earth (KOI-1977.02/Kepler-345 b). These results demonstrate the power of photodynamical modeling with the appropriately chosen degrees of freedom. This will become increasingly more important as smaller planets are detected, especially as the TESS mission gathers ever longer baseline light curves and for the analysis of the future PLATO mission data.

TESS Giants Transiting Giants. VII. A Hot Saturn Orbiting an Oscillating Red Giant Star**This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Abstract We present the discovery of TOI-7041 b (TIC 201175570 b), a hot Saturn transiting a red giant star with measurable stellar oscillations. We observe solar-like oscillations in TOI-7041 with a frequency of maximum power of ν max = 218.50 ± 2.23 μHz and a large frequency separation of Δν = 16.5282 ± 0.0186 μHz. Our asteroseismic analysis indicates that TOI-7041 has a mass of 1.07 ± 0.05(stat) ± 0.02(sys) M ⊙ and a radius of 4.10 ± 0.06(stat) ± 0.05(sys) R ⊙, making it one of the largest stars around which a transiting planet has been discovered with the Transiting Exoplanet Survey Satellite (TESS), and the mission's first oscillating red giant with a transiting planet. TOI-7041 b has an orbital period of 9.691 ± 0.006 days and a low eccentricity of e = 0.04 ± 0.04. We measure a planet radius of 1.02 ± 0.03 R Jup with TESS photometry, and a planet mass of 0.36 ± 0.16 M Jup (114 ± 51 M ⊕) with ground-based radial velocity measurements. TOI-7041 b appears less inflated than similar systems receiving equivalent incident flux, and its circular orbit indicates that it is not undergoing tidal heating due to circularization. The asteroseismic analysis of the host star provides some of the tightest constraints on the stellar properties of a TESS planet host and enables precise characterization of the hot Saturn. This system joins a small number of TESS-discovered exoplanets orbiting stars that exhibit clear stellar oscillations and indicates that extended TESS observations of evolved stars will similarly provide a path to improved exoplanet characterization.

Predictions of Dust Continuum Emission from a Potential Circumplanetary Disk: A Case Study of the Planet Candidate AB Aurigae b

Abstract Gas-accreting planets embedded in protoplanetary disks are expected to show dust thermal emission from their circumplanetary disks (CPDs). However, a recently reported gas-accreting planet candidate, AB Aurigae b, has not been detected in (sub)millimeter continuum observations. We calculate the evolution of dust in the potential CPD of AB Aurigae b and predict its thermal emission at 1.3 mm wavelength as a case study, where the obtained features may also be applied to other gas-accreting planets. We find that the expected flux density from the CPD is lower than the 3σ level of the previous continuum observation by the Atacama Large Millimeter/submillimeter Array with broad ranges of parameters, consistent with a nondetection. However, the expected planet mass and gas accretion rate are higher if the reduction of the observed near-infrared continuum and Hα line emission due to the extinction by small grains is considered, resulting in higher flux density of the dust emission from the CPD at (sub)millimeter wavelengths. We find that the corrected predictions of the dust emission are stronger than the 3σ level of the previous observation with the typical dust-to-gas mass ratio of the inflow to the CPD. This result suggests that the dust supply to the vicinity of AB Aurigae b is small if the planet candidate is not the scattered light of the star but is a planet and has a CPD. Future continuum observations at shorter wavelengths are required to obtain more robust clues to the question of whether the candidate is a planet or not.

Separating Super-puffs versus Hot Jupiters among Young Puffy Planets

Abstract Discoveries of close-in young puffy (R p ≳ 6 R ⊕) planets raise the question of whether they are bona fide hot Jupiters or puffed-up Neptunes, potentially placing constraints on the formation location and timescale of hot Jupiters. Obtaining mass measurements for these planets is challenging due to stellar activity and noisy spectra. Therefore, we aim to provide independent theoretical constraints on the masses of these young planets based on their radii, incident fluxes, and ages, benchmarking to the planets of age <1 Gyr detected by Kepler, K2, and the Transiting Exoplanet Survey Satellite. Through a combination of interior structure models, considerations of photoevaporative mass loss, and empirical mass–metallicity trends, we present the range of possible masses for 22 planets with an age of ∼10–900 Myr and radii of ∼6–16 R ⊕. We generally find that our mass estimates are in agreement with the measured masses and upper limits where applicable. There exist some outliers including super-puffs Kepler-51 b, c and V1298 Tau d, b, e, for which we outline their likely formation conditions. Our analyses demonstrate that most of the youngest planets (≲100 Myr) tend to be puffed-up, Neptune-mass planets, while the true hot Jupiters are typically found around stars aged at least a few hundred Myr, suggesting the dominant origin of hot Jupiters to be late-stage high-eccentricity migration.

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.

Detection and characterization of giant planets with Gaia astrometry

ABSTRACT Astrometric observations with Gaia are expected to play a valuable role in future exoplanet surveys. With current data from Gaia’s third data release (DR3), we are sensitive to periods from less than 1 yr to more than 4 yr but, unlike radial velocity (R.V.) are not as restricted by the orbital inclination of a potential planet. The presence and potential properties of a companion affect the primary’s renormalized unit weight error (RUWE) making this a valuable quantity in the search for exoplanets. Using this value and the fitted astrometric tracks from Gaia, we use Bayesian inference to constrain the mass and orbital parameters of companions in known systems. Combining this with R.V. measurements, we show it is possible to independently measure mass and inclination and suggest HD 66141 b is a possible brown dwarf with maximum mass 23.9$^{+7.2}_{-6.4}$ $\mathrm{ M}_{\mathrm{J}}$. We show how this method may be applied to directly imaged planets in the future, using $\beta$-Pictoris c as an example but note that the host star is bright and active, making it difficult to draw clear conclusions. We show how the next Gaia data release, which will include epoch astrometry, will allow us to accurately constrain orbital parameters from astrometric data alone, revolutionizing future searches for exoplanets. Combining predicted observational limits on planet mass with theoretical distributions, we estimate the probability that a star with a given RUWE will host a detectable planet, which will be highly valuable in planning future surveys.

Enhanced Stability in Planetary Systems with Similar Masses

Abstract This study employs numerical simulations to explore the relationship between the dynamical instability of planetary systems and the uniformity of planetary masses within the system, quantified by the Gini index. Our findings reveal a significant correlation between system stability and mass uniformity. Specifically, planetary systems with higher mass uniformity demonstrate increased stability, particularly when they are distant from first-order mean motion resonances. In general, for nonresonant planetary systems with a constant total mass, non-equal-mass systems are less stable than equal mass systems for a given spacing in units of mutual Hill radius. This instability may arise from the equipartition of the total random energy, which can lead to higher eccentricities in smaller planets, ultimately destabilizing the system. This work suggests that the observed mass uniformity within multiplanet systems detected by Kepler may result from a combination of survival bias and ongoing dynamical evolution processes.