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The lack of close-in Neptune-mass exoplanets evident in transit surveys has largely been attributed to either photoevaporative mass loss or high-eccentricity migration. To distinguish between these two possibilities, we investigate the origins of TOI-1259 A b, a Saturn-mass (0.4 M _J , 1.0 R _J ) exoplanet lying along the upper edge of the Neptune desert. TOI-1259 A b's close-in ( P = 3.48 days) orbit and low bulk density make the planet particularly vulnerable to photoevaporation. We studied the upper atmosphere of TOI-1259 A b using metastable helium 1083 nm transits observed with Palomar/WIRC and Keck/NIRSPEC. We report a band-integrated excess absorption of 0.395% ± 0.072% with Palomar/WIRC and a spectroscopically resolved 5.5 ± 0.94 km s ^−1 blueshifted absorption of 2.4% ± 0.52% ( T _1 – T _4 ) and 3.5% ± 0.72% ( T _2 – T _3 ) with Keck/NIRSPEC. These measurements indicate the presence of an extended escaping atmosphere. Fitting these signals with a Parker wind model, we determine a corresponding atmospheric mass-loss rate of log( $\dot{M}$ ) = 10.2–10.65 g s ^−1 for thermosphere temperatures between 7900 and 8600 K. This relatively low rate suggests that this planet would not have been significantly altered by mass loss even if it formed in situ. However, the presence of a white dwarf companion, TOI-1259 B, hints that this planet may not have formed close-in, but rather migrated inward relatively late. Given the estimated parameters of the proto−white dwarf companion, we find that high-eccentricity migration is possible for the system.

Super-Earths are highly irradiated, small planets with bulk densities approximately consistent with Earth. We construct combined interior atmosphere models of super-Earths that trace the partitioning of water throughout a planet, including an iron-rich core, silicate-rich mantle, and steam atmosphere. We compare these models with exoplanet observations to infer a 1 σ upper limit on the total water mass fraction of ≲3% at the population level. We consider end-member scenarios that may change this value, including the efficiency of mantle outgassing, escape of high mean molecular weight atmospheres, and increased iron core mass fractions. Although our constraints are agnostic as to the origin of water, we show that our upper limits are consistent with its production via chemical reactions of primordial hydrogen-dominated atmospheres with magma oceans. This mechanism has also been hypothesised to explain Earth's water content, possibly pointing to a unified channel for the origins of water on small terrestrial planets.

A fundamental question in the study of planetary system demographics is: how common is the solar system architecture? The primary importance of this question lies in the potential of planetary systems to create habitable environments, and dissecting the various components of solar system evolution that contributed to a sustainable temperate surface for Earth. One important factor in that respect is volatile delivery to the inner system and the dependence on giant planets beyond the snow line as scattering agents, particularly as such cold giant planets are relatively rare. Here, we provide an investigation of the eccentricity distribution for giant planet populations both interior and exterior to their system snow lines. We show that the median eccentricity for cold giants is 0.23, compared with a far more circular orbital regime for inner planets. We further present the results of a dynamical simulation that explores the particle scattering potential for a Jupiter analog in comparison with a Jupiter whose eccentricity matches that of the median cold giant eccentricity. These simulations demonstrate that the capacity for such an eccentric cold giant system to scatter volatiles interior to the snow line is significantly increased compared with the Jupiter analog case, resulting in a far greater volume of Earth-crossing volatiles. Thus, many of the known systems with cold giant planets may harbor water worlds interior to the snow line.

The ubiquity of “peas-in-a-pod” architectural patterns and the existence of the radius valley each presents a striking population-level trend for planets with R _p ≤ 4 R _⊕ that serves to place powerful constraints on the formation and evolution of these subgiant worlds. As it has yet to be determined whether the strength of this peas-in-a-pod uniformity differs on either side of the radius valley, we separately assess the architectures of systems containing only small ( R _p ≤ 1.6 R _⊕ ), rocky planets from those harboring only intermediate-sized (1.6 R _⊕ < R _p ≤ 4 R _⊕ ), volatile-rich worlds to perform a novel statistical comparison of intra-system planetary uniformity across compositionally distinct regimes. We find that, compared to their volatile-rich counterparts, rocky systems are less uniform in mass (2.6 σ ) but more uniform in size (4.0 σ ) and spacing (3.0 σ ). We provide further statistical validation for these results, demonstrating that they are not substantially influenced by the presence of mean-motion resonances, low-mass host stars, alternative bulk compositional assumptions, sample size effects, or detection biases. We also obtain tentative evidence (>2 σ significance) that the enhanced size uniformity of rocky systems is dominated by the presence of super-Earths (1 R _⊕ ≤ R _p ≤ 1.6 R _⊕ ), while their enhanced mass diversity is driven by the presence of sub-Earth ( R _p < 1 R _⊕ ) worlds.

The stellar obliquity distribution of warm-Jupiter systems is crucial for constraining the dynamical history of Jovian exoplanets, as the warm Jupiters’ tidal detachment likely preserves their primordial obliquity. However, the sample size of warm-Jupiter systems with measured stellar obliquities has historically been limited compared to that of hot Jupiters, particularly in hot-star systems. In this work, we present newly obtained sky-projected stellar obliquity measurements for the warm-Jupiter systems TOI-559, TOI-2025, TOI-2031, TOI-2485, TOI-2524, and TOI-3972, derived from the Rossiter–McLaughlin effect, and show that all six systems display alignment with a median measurement uncertainty of 13°. Combining these new measurements with the set of previously reported stellar obliquity measurements, our analysis reveals that single-star warm-Jupiter systems tend to be aligned, even around hot stellar hosts. This alignment exhibits a 3.4 σ deviation from the T _eff – λ dependency observed in hot-Jupiter systems, where planets around cool stars tend to be aligned, while those orbiting hot stars show considerable misalignment. The current distribution of spin–orbit measurements for Jovian exoplanets indicates that misalignments are neither universal nor primordial phenomena affecting all types of planets. The absence of misalignments in single-star warm-Jupiter systems further implies that many hot Jupiters, by contrast, have experienced a dynamically violent history.

The youngest (

The Kepler and K2 missions enabled robust calculations of planet occurrence rates around FGKM-type stars. However, these missions observed too few stars with earlier spectral types to tightly constrain the occurrence rates of planets orbiting hotter stars. Using TESS, we calculate the occurrence rate of small (1 R _⊕

Before the launch of the Kepler Space Telescope, models of low-mass planet formation predicted that convergent type I migration would often produce systems of low-mass planets in low-order mean-motion resonances. Instead, Kepler discovered that systems of small planets frequently have period ratios larger than those associated with mean-motion resonances and rarely have period ratios smaller than those associated with mean-motion resonances. Both short-timescale processes related to the formation or early evolution of planetary systems and long-timescale secular processes have been proposed as explanations for these observations. Using a thin disk stellar population’s Galactic velocity dispersion as a relative age proxy, we find that Kepler-discovered multiple-planet systems with at least one planet pair near a period ratio suggestive of a second-order mean-motion resonance have a colder Galactic velocity dispersion and are therefore younger than both single-transiting and multiple-planet systems that lack planet pairs consistent with mean-motion resonances. We argue that a nontidal secular process with a characteristic timescale no less than a few hundred Myr is responsible for moving systems of low-mass planets away from second-order mean-motion resonances. Among systems with at least one planet pair near a period ratio suggestive of a first-order mean-motion resonance, only the population of systems likely affected by tidal dissipation inside their innermost planets has a small Galactic velocity dispersion and is therefore young. We predict that period ratios suggestive of mean-motion resonances are more common in young systems with 10 Myr ≲ τ ≲ 100 Myr and become less common as planetary systems age.

An intriguing pattern among exoplanets is the lack of detected planets between approximately 1.5 R _⊕ and 2.0 R _⊕ . One proposed explanation for this “radius gap” is the photoevaporation of planetary atmospheres, a theory that can be tested by studying individual planetary systems. Kepler-105 is an ideal system for such testing due to the ordering and sizes of its planets. Kepler-105 is a Sun-like star that hosts two planets straddling the radius gap in a rare architecture with the larger planet closer to the host star ( R _b = 2.53 ± 0.07 R _⊕ , P _b = 5.41 days, R _c = 1.44 ± 0.04 R _⊕ , P _c = 7.13 days). If photoevaporation sculpted the atmospheres of these planets, then Kepler-105b would need to be much more massive than Kepler-105c to retain its atmosphere, given its closer proximity to the host star. To test this hypothesis, we simultaneously analyzed radial velocities and transit-timing variations of the Kepler-105 system, measuring disparate masses of M _b = 10.8 ± 2.3 M _⊕ ( ρ _b = 3.68 ± 0.84 g cm ^−3 ) and M _c = 5.6 ± 1.2 M _⊕ ( ρ _c = 10.4 ± 2.39 g cm ^−3 ). Based on these masses, the difference in gas envelope content of the Kepler-105 planets could be entirely due to photoevaporation (in 76% of scenarios), although other mechanisms like core-powered mass loss could have played a role for some planet albedos.

As stars evolve to higher luminosities during first ascension of the giant branch, previously frozen terrestrial worlds may thaw and host liquid water on their surfaces. Eventually these outer worlds again become uninhabitable due to receiving too much incident light and their water inventory evaporating. Solar-mass stars experience a sudden decrease in luminosity entering the horizontal branch, which could result in a secondary habitable phase for their outer worlds. The outer worlds’ time with habitable surface climates is key in evaluating the possibility of extraterrestrial life arising. The times inside the habitable zone (TIHZ) are calculated for outer worlds orbiting between 5 and 45 au around a Sun-like star. By comparing the TIHZ to time estimates for life to arise on Earth, we evaluate whether such outer worlds are promising candidates in the search for extraterrestrial life. We use two different solar evolution models (PARSEC and Dartmouth) and both optimistic and conservative habitable zone (HZ) definitions. Multiple habitable phases are found for each outer world. Outer worlds with orbits as large as Saturn are found to have a secondary habitable phase which exceeds the first in duration. Generally, the time inside the HZ is found to decrease almost monotonically with orbiting distance. Water loss is calculated after the first habitable phase to determine whether a secondary habitable phase is possible. For all orbiting distances the water loss is insufficient to deplete a water inventory equivalent to that of many moons in the outer solar system.

Within the first few hundreds of millions of years, many physical processes sculpt the eventual properties of young planets. NASA’s Transiting Exoplanet Survey Satellite (TESS) mission has surveyed young stellar associations across the entire sky for transiting planets, providing glimpses into the various stages of planetary evolution. Using our own detection pipeline, we search a magnitude-limited sample of 7219 young stars (≲200 Myr) observed in the first 4 yr of TESS for small (2–8 R _⊕ ), short period (1.6–20 days) transiting planets. The completeness of our survey is characterized by a series of injection and recovery simulations. Our analysis of TESS 2 minute cadence and Full Frame Image (FFI) light curves recover all known TESS Objects of Interest (TOIs), as well as four new planet candidates not previously identified as TOIs. We derive an occurrence rate of ${35}_{-10}^{+13} \% $ for mini-Neptunes and ${27}_{-8}^{+10} \% $ for super-Neptunes from the 2 minute cadence data, and ${22}_{-6.8}^{+8.6}$ % for mini-Neptunes and ${13}_{-4.9}^{+3.9}$ % for super-Neptunes from the FFI data. To independently validate our results, we compare our survey yield with the predicted planet yield assuming Kepler planet statistics. We consistently find a mild increase in the occurrence of super-Neptunes and a significant increase in the occurrence of Neptune-sized planets with orbital periods of 6.2–12 days when compared to their mature counterparts. The young planet distribution from our study is most consistent with evolution models describing the early contraction of hydrogen-dominated atmospheres undergoing atmospheric escape and inconsistent with heavier atmosphere models offering only mild radial contraction early on.

A planet’s mass loss is important for the its formation and evolution. The radius valley (RV) is believed to be triggered by evaporation-induced mass loss. As an alternative mechanism for RV, the mass loss of post-impact planets is thoroughly investigated in this work. The impact energy is converted to the planet’s internal energy, enhancing its core energy and accelerating mass loss and orbital migration. As the host star changes from K type to F type, the planet’s mass loss and orbital migration increase. When the initial gas-to-core-mass ratio is small, the migration efficiency for planets around K-type stars will increase, which helps to suppress mass loss and retain the planet’s mass and radius within a specific range. On the contrary, planets around more massive F-type stars experience more substantial mass loss, potentially leading to complete mass loss, and migrate to orbits with longer periods. Our calculation shows that planets around different spectral types of host stars give rise to an RV ranging from 1.3 to 2.0 R _⊕ , consistent with the observed range of 1.3–2.6 R _⊕ . Despite the presence of uncertain parameters, the planetesimal impact can promote the RV establishment for planets around host stars of different spectral types.

The Kepler mission enabled us to look at the intrinsic population of exoplanets within our galaxy. In period-radius space, the distribution of the intrinsic population of planets contains structure that can trace planet formation and evolution history. The most distinctive feature in period-radius space is the radius cliff, a steep drop-off in occurrence between 2.5 and 4 R _⊕ across all period ranges, separating the sub-Neptune population from the rarer Neptunes orbiting within 1 au. Following our earlier work to measure the occurrence rate of the Kepler population, we characterize the shape of the radius cliff as a function of orbital period (10–300 days) as well as insolation flux (9500 S _⊕ –10 S _⊕ ). The shape of the cliff flattens at longer orbital periods, tracking the rising population of Neptune-sized planets. In insolation, however, the radius cliff is both less dramatic and the slope is more uniform. The difference in this feature between period space and insolation space can be linked to the effect of EUV/X-ray versus bolometric flux in the planet’s evolution. Models of atmospheric mass loss processes that predict the location and shape of the radius valley also predict the radius cliff. We compare our measured occurrence rate distribution to population synthesis models of photoevaporation and core-powered mass loss in order to constrain formation and evolution pathways. We find that the models do not statistically agree with our occurrence distributions of the radius cliff in period space or insolation space. Atmospheric mass loss that shapes the radius valley cannot fully explain the shape of the radius cliff.

The degree of alignment between a star’s spin axis and the orbital plane of its planets (the stellar obliquity) is related to interesting and poorly understood processes that occur during planet formation and evolution. Hot Jupiters orbiting hot stars (≳6250 K) display a wide range of obliquities, while similar planets orbiting cool stars are preferentially aligned. Tidal dissipation is expected to be more rapid in stars with thick convective envelopes, potentially explaining this trend. Evolved stars provide an opportunity to test the damping hypothesis, particularly stars that were hot on the main sequence and have since cooled and developed deep convective envelopes. We present the first systematic study of the obliquities of hot Jupiters orbiting subgiants that recently developed convective envelopes using Rossiter–McLaughlin observations. Our sample includes two newly discovered systems in the Giants Transiting Giants survey (TOI-6029 b, TOI-4379 b). We find that the orbits of hot Jupiters orbiting subgiants that have cooled below ∼6250 K are aligned or nearly aligned with the spin axis of their host stars, indicating rapid tidal realignment after the emergence of a stellar convective envelope. We place an upper limit for the timescale of realignment for hot Jupiters orbiting subgiants at ∼500 Myr. Comparison with a simplified tidal evolution model shows that obliquity damping needs to be ∼4 orders of magnitude more efficient than orbital period decay to damp the obliquity without destroying the planet, which is consistent with recent predictions for tidal dissipation from inertial waves excited by hot Jupiters on misaligned orbits.

We used the database of 1040 short-period (1 ≤ P < 200 days) exoplanets radial-velocity orbits to study the planetary eccentricity-period (PEP) distribution. We first divided the sample into low- and high-mass exoplanet subsamples based on the distribution of the (minimum) planetary masses, which displays a clear two-Gaussian distribution, separated at 0.165 M _J . We then selected 216 orbits, low- and high-mass alike, with eccentricities significantly distinct from circular orbits. The 131 giant-planet eccentric orbits display a clear upper envelope, which we model quantitatively, rises monotonically from zero eccentricity and reaches an eccentricity of 0.8 at P ∼ 100 days. Conversely, the 85 low-mass planetary orbits display a flat eccentricity distribution between 0.1 and 0.5, with almost no dependence on the orbital period. We show that the striking difference between the two PEP distributions is not a result of the detection technique used. The upper envelope of the high-mass planets, also seen in short-period binary stars, is a clear signature of tidal circularization, which probably took place inside the planets, while the small-planet PEP distribution suggests that the circularization was not effective, probably due to dynamical interactions with neighboring planets.

Close-in planets smaller than Neptune form two distinct populations composed of rocky super-Earths and sub-Neptunes that may host primordial H/He envelopes. The origin of the radius valley separating these two planet populations remains an open question and has been posited to emerge either directly from the planet formation process or via subsequent atmospheric escape. Multitransiting systems that span the radius valley are known to be useful diagnostics of XUV-driven mass loss. Here, we extend this framework to test XUV-driven photoevaporation, core-powered mass loss, and an accretion-limited primordial radius valley model. Focusing on multitransiting systems allows us to eliminate unobservable quantities that are shared within individual systems such as stellar XUV luminosity histories and the properties of the protoplanetary disk. We test each proposed radius valley emergence mechanism on all 221 known multitransiting systems and calculate the minimum masses of the systems’ enveloped planets to be consistent with the models. We compare our model predictions to 75 systems with measured masses and find that the majority of systems can be explained by any of the three proposed mechanisms. We also examine model consistency as a function of stellar mass and stellar metallicity but find no significant trends. More multitransiting systems with mass characterizations are required before multitransiting systems can serve as a viable diagnostic of radius valley emergence models. Our software for the model evaluations presented herein is available on GitHub and may be applied to future multitransiting system discoveries.

We report the discovery of a super-Jovian 2:1 mean-motion resonance (MMR) pair around the G-type star TIC 279401253, whose dynamical architecture is a prospective benchmark for planet formation and orbital evolution analysis. The system was discovered thanks to a single-transit event recorded by the Transiting Exoplanet Survey Satellite mission, which pointed to a Jupiter-sized companion with poorly constrained orbital parameters. We began ground-based precise radial velocity (RV) monitoring with HARPS and FEROS within the Warm gIaNts with tEss survey to constrain the transiting body’s period, mass, and eccentricity. The RV measurements revealed not one but two massive planets with periods of ${76.80}_{-0.06}^{+0.06}$ and ${155.3}_{-0.7}^{+0.7}$ days, respectively. A combined analysis of transit and RV data yields an inner transiting planet with a mass of ${6.14}_{-0.42}^{+0.39}$ M _Jup and a radius of ${1.00}_{-0.04}^{+0.04}$ R _Jup , and an outer planet with a minimum mass of ${8.02}_{-0.18}^{+0.18}$ M _Jup , indicating a massive giant pair. A detailed dynamical analysis of the system reveals that the planets are locked in a strong first-order, eccentricity-type 2:1 MMR, which makes TIC 279401253 one of the rare examples of truly resonant architectures supporting disk-induced planet migration. The bright host star, V ≈ 11.9 mag, the relatively short orbital period ( P _b = ${76.80}_{-0.06}^{+0.06}$ days), and pronounced eccentricity ( e = 0.448 ${}_{-0.029}^{+0.028}$ ) make the transiting planet a valuable target for atmospheric investigation with the James Webb Space Telescope and ground-based extremely large telescopes.

The hot Saturn population exhibits a boundary in mass–radius space, such that no planets are observed at a density less than ∼0.1 g cm ^−3 . Yet, planet interior structure models can readily construct such objects as the natural result of radius inflation. Here, we investigate the role X-ray and extreme UV irradiation (XUV)-driven mass loss plays in sculpting the density boundary by constructing interior structure models that include radius inflation, photoevaporative mass loss, and a simple prescription of Roche lobe overflow. We demonstrate that planets puffier than ∼0.1 g cm ^−3 experience a runaway mass loss caused by adiabatic radius expansion as the gas layer is stripped away, providing a good explanation of the observed edge in mass–radius space. The process is also visible in the radius–period and mass–period spaces, though smaller, high-bulk-metallicity planets can still survive at short periods, preserving a partial record of the population distribution at formation.

Irradiated Jovian atmospheres are complex and dynamic and can undergo temporal variations due to the close proximity of their parent stars. Of the Jovian planets that have been cataloged to date, KELT-9b is the hottest gas giant known, with an equilibrium temperature of 4050 K. We probe the temporal variability of transmission spectroscopic signatures from KELT-9b via a set of archival multiyear ground-based transit observations, performed with the TRES facility on the 1.5 m reflector at the Fred Lawrence Whipple Observatory. Our observations confirm past detections of Fe i , Fe ii , and Mg i over multiple epochs, in addition to excess absorption at H α , which is an indicator for ongoing mass loss. From our multiyear data set, the H α light curve consistently deviates from a standard transit and follows a “W” shape that is deeper near ingress and egress and shallower midtransit. To search for and quantify any seasonal variations that may be present, we parameterize a “cometary tail” model to fit for the H α transit. We find no detectable variations between the different observed epochs. Though a “cometary tail” describes the H α flux variations well, we note that such a scenario requires a high density of neutral hydrogen in the n = 2 excited state far beyond the planetary atmosphere. Other scenarios, such as center-to-limb variations larger than that expected from 1D atmosphere models, may also contribute to the observed H α transit shape. These multiepoch observations highlight the capabilities of small telescopes to provide temporal monitoring of the dynamics of exoplanet atmospheres.

A planet’s history dictates its current potential to host habitable conditions and life. The concept of the continuously habitable zone (CHZ) has been used to define the region around a star most likely to host planets with long-term habitability. However, definitions of the CHZ vary in the literature and often conflict with each other. Calculating the fraction of habitable zone planets in the CHZ as a function of stellar properties, we find that the quality of a star as a host for planets with long-term habitability and biosignatures depends strongly on the formulation of the CHZ used. For instance, older M stars are either excellent or suboptimal hosts for CHZ planets, depending on whether one’s definition of habitability prioritizes the total time spent in the habitable zone or the continuity of habitable conditions from the delivery of volatiles to its current age. In this study, we focus on belatedly habitable zone (BHZ) planets, i.e., planets that enter the habitable zone after formation due to the evolution of their host star. We find that between ∼29% and 74% of planets in the habitable zone belong to this class of BHZ planets, depending on the timescale for the delivery of volatiles. Whether these planets can retain their volatiles and support habitable conditions is unclear. Since BHZ planets comprise a large portion of the planets we expect to survey for biosignatures with future missions, the open question of their habitability is an important factor for mission design, survey strategies, and the interpretation of results.

Characterizing the bulk compositions of transiting exoplanets within the M dwarf radius valley offers a unique means to establish whether the radius valley emerges from an atmospheric mass-loss process or is imprinted by planet formation itself. We present the confirmation of such a planet orbiting an early-M dwarf ( T _mag = 11.0294 ± 0.0074, M _s = 0.513 ± 0.012 M _⊙ , R _s = 0.515 ± 0.015 R _⊙ , and T _eff = 3690 ± 50 K): TOI-1695 b ( P = 3.13 days and ${R}_{p}={1.90}_{-0.14}^{+0.16}\ {R}_{\oplus }$ ). TOI-1695 b’s radius and orbital period situate the planet between model predictions from thermally driven mass loss versus gas depleted formation, offering an important test case for radius valley emergence models around early-M dwarfs. We confirm the planetary nature of TOI-1695 b based on five sectors of TESS data and a suite of follow-up observations including 49 precise radial velocity measurements taken with the HARPS-N spectrograph. We measure a planetary mass of 6.36 ± 1.00 M _⊕ , which reveals that TOI-1695 b is inconsistent with a purely terrestrial composition of iron and magnesium silicate, and instead is likely a water-rich planet. Our finding that TOI-1695 b is not terrestrial is inconsistent with the planetary system being sculpted by thermally driven mass loss. We present a statistical analysis of seven well-characterized planets within the M dwarf radius valley demonstrating that a thermally driven mass-loss scenario is unlikely to explain this population.

We present Kepler exoplanet occurrence rates for planets between 0.5 and 16 R _⊕ and between 1 and 400 days. To measure occurrence, we use a nonparametric method via a kernel density estimator and use bootstrap random sampling for uncertainty estimation. We use a full characterization of completeness and reliability measurements from the Kepler Data Release 25 catalog, including detection efficiency, vetting completeness, astrophysical reliability, and false alarm reliability. We also include more accurate and homogeneous stellar radii from Gaia Data Release 2. In order to see the impact of these final Kepler properties, we revisit benchmark exoplanet occurrence rate measurements from the literature. We compare our measurements with previous studies to both validate our method and observe the dependence of these benchmarks on updated stellar and planet properties. For FGK stars, between 0.5 and 16 R _⊕ and between 1 and 400 days, we find an occurrence of 1.52 ± 0.08 planets per star. We investigate the dependence of occurrence as a function of radius, orbital period, and stellar type and compare with previous studies with excellent agreement. We measure the minimum of the radius valley to be ${1.78}_{-0.16}^{+0.14}$ R _⊕ for FGK stars and find it to move to smaller radii for cooler stars. We also present new measurements of the slope of the occurrence cliff at 3–4 R _⊕ , and find that the cliff becomes less steep at long orbital period. Our methodology will enable us to constrain theoretical models of planet formation and evolution in the future.

The engulfment of substellar bodies (SBs), such as brown dwarfs and planets, by giant stars is a possible explanation for rapidly rotating giants, lithium-rich giants, and the presence of SBs in close orbits around subdwarfs and white dwarfs. We perform three-dimensional hydrodynamical simulations of the flow in the vicinity of an engulfed SB. We model the SB as a rigid body with a reflective surface because it cannot accrete. This reflective boundary changes the flow morphology to resemble that of engulfed compact objects with outflows. We measure the drag coefficients for the ram-pressure and gravitational drag forces acting on the SB, and use them to integrate its trajectory inside the star. We find that engulfment can increase the luminosity of a 1 M _⊙ star by up to a few orders of magnitude. The time for the star to return to its original luminosity is up to a few thousand years when the star has evolved to ≈10 R _⊙ and up to a few decades at the tip of the red giant branch (RGB). No SBs can eject the envelope of a 1 M _⊙ star before it evolves to ≈10 R _⊙ if the orbit of the SB is the only energy source contributing to the ejection. In contrast, SBs as small as ≈10 M _Jup can eject the envelope at the tip of the RGB. The numerical framework we introduce here can be used to study planetary engulfment in a simplified setting that captures the physics of the flow at the scale of the SB.

The search for exoplanets has revealed a diversity of planetary system architectures, the vast majority of which diverge significantly from the template of the solar system. In particular, giant planets beyond the snow line are relatively rare, especially for low-mass stars, placing the solar system within a small category of systems with multiple giant planets at large separations. An exoplanetary system of note is that of HD 141399, consisting of a K-dwarf host star that harbors four giant planets with separations extending to ∼4.5 au. The architecture of the system creates a complex pattern of mean motion resonances and gravitationally perturbed regions that may exclude the presence of other planets, including within the habitable zone of the system. Here, we present the results of dynamical simulations that explore the interaction of the known planets of the system, their apsidal trajectories, resonance locations, and dynamical evolution. We further investigate the results of injecting Earth-mass planets and provide the regions of dynamical viability within the habitable zone where terrestrial planets may maintain long-term stability. We discuss these results in the context of the importance of giant planets for volatile delivery and planetary habitability considerations.

We investigate how the occurrence rate of giant planets (minimum mass > 0.3 M _Jup ) around Sun-like stars depends on the age, mass, and metallicity of their host stars. We develop a hierarchical Bayesian framework to infer the number of planets per star (NPPS) as a function of both planetary and stellar parameters. The framework fully takes into account the uncertainties in the latter by utilizing the posterior samples for the stellar parameters obtained by fitting stellar isochrone models to the spectroscopic parameters, Gaia DR3 parallaxes, and 2MASS K _s -band magnitudes adopting a certain bookkeeping prior. We apply the framework to 46 Doppler giants found around a sample of 382 Sun-like stars from the California Legacy Survey catalog that publishes spectroscopic parameters and search completeness for all the surveyed stars. We find evidence that the NPPS of hot Jupiters (orbital period P = 1–10 days) decreases roughly in the latter half of the main sequence over the timescale of ${ \mathcal O }(\mathrm{Gyr})$ , while that of cold Jupiters ( P = 1–10 yr) does not. Assuming that this decrease is real and caused by tidal orbital decay, the modified stellar tidal quality factor ${Q}_{\star }^{{\prime} }$ is implied to be ${ \mathcal O }({10}^{6})$ for a Sun-like main-sequence star orbited by a Jupiter-mass planet with P ≈ 3 days.

Planets in young star clusters could shed light on planet formation and evolution since star clusters can provide accurate age estimation. However, the number of transiting planets detected in clusters was only ∼30, too small for statistical analysis. Thanks to the unprecedented high-precision astrometric data provided by Gaia DR2 and Gaia DR3, many new open clusters (OCs) and comoving groups have been identified. The Understanding Planetary Formation and Evolution in Star Clusters project aims to find observational evidence and interpret how planets form and evolve in cluster environments. In this work, we cross match the stellar catalogs of new OCs and comoving groups with confirmed planets and candidates. We carefully remove false positives and obtain the biggest catalog of planets in star clusters up to now, which consists of 73 confirmed planets and 84 planet candidates. After age validation, we obtain the radius–age diagram of these planets/candidates. We find an increment in the fraction of hot Jupiters (HJs) around 100 Myr and attribute the increment to the flyby-induced high- e migration in star clusters. An additional small bump of the fraction of HJs after 1 Gyr is detected, which indicates the formation timescale of HJ around field stars is much larger than that in star clusters. Thus, stellar environments play important roles in the formation of HJs. The hot Neptune desert occurs around 100 Myr in our sample. A combination of photoevaporation and high- e migration may sculpt the hot Neptune desert in clusters.

Sub-Neptune exoplanets may have thick hydrogen envelopes and therefore develop a high-pressure interface between hydrogen and the underlying silicates/metals. Some sub-Neptunes may convert to super-Earths via massive gas loss. If hydrogen chemically reacts with oxides and metals at high pressures and temperatures ( P − T ), it could impact the structure and composition of the cores and atmospheres of sub-Neptunes and super-Earths. While H _2 gas is a strong reducing agent at low pressures, the behavior of hydrogen is unknown at the P − T expected for sub-Neptunes’ interiors, where hydrogen is a dense supercritical fluid. Here we report experimental results of reactions between ferrous/ferric oxides and hydrogen at 20–40 GPa and 1000–4000 K utilizing the pulsed laser-heated diamond-anvil cell combined with synchrotron X-ray diffraction. Under these conditions, hydrogen spontaneously strips iron off the oxides, forming Fe-H alloys and releasing oxygen to the hydrogen medium. In a planetary context where this reaction may occur, the Fe-H alloy may sink to the metallic part of the core, while released oxygen may stabilize as water in the silicate layer, providing a mechanism to ingas hydrogen to the deep interiors of sub-Neptunes. Water produced from the redox reaction can also partition to the atmosphere of sub-Neptunes, which has important implications for understanding the composition of their atmospheres. In addition, super-Earths converted from sub-Neptunes may contain a large amount of hydrogen and water in their interiors (at least a few wt% H _2 O). This is distinct from smaller rocky planets, which were formed relatively dry (likely a few hundredths wt% H _2 O).