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Super-Earths orbiting M dwarf stars may be the most common habitable planets in the Universe. However, their habitability is threatened by intense irradiation from their host stars, which drives the escape of water to space and can lead to surface desiccation. We present simulation results of a box model incorporating deep-water cycling between interior and atmosphere and water loss to space for terrestrial planets of mass 1–8 M ⊕ orbiting in the habitable zone of a late M dwarf. Energy-limited loss decreases with planetary mass, while diffusion-limited loss increases with mass. Depending on where it orbits in the habitable zone, a 1 M ⊕ planet that starts with 3–8 Earth Oceans can end up with an Earthlike surface of oceans and exposed continents; for an 8 M ⊕ super-Earth, that range is 3–12 Earth Oceans. Planets initialized with more water end up as waterworlds with no exposed continents, while planets that start with less water have desiccated surfaces by 5 Gyr. Since the mantles of terrestrial planets can hold much more water than is currently present in Earth's atmosphere, none of our simulations result in Dune planets—such planets may be less common than previously thought. Further, more water becomes sequestered within the mantle for larger planets. A super-Earth at the inner edge of the habitable zone tends to end up as either a waterworld or with a desiccated surface; only a narrow range of initial water inventory yields an Earthlike surface. [ABSTRACT FROM AUTHOR]

Over 200 protoplanetary disk systems have been resolved by the Atacama Large Millimeter/submillimeter Array (ALMA), and the vast majority suggest the presence of planets. The dust gaps in transition disks are considered evidence of giant planets sculpting gas and dust under appropriate disk viscosity. However, the unusually high accretion rates in many T Tauri stars hosting transition disks challenge this theory. As the only disk currently observed with high turbulence, the high accretion rate (∼10−8.3 M ⊙ yr−1) observed in DM Tau indicates the presence of strong turbulence within the system. Considering the recent theoretical advancements in magnetized disk winds are challenging the traditional gap-opening theories and viscosity-driven accretion models, our study presents a pioneering simulation incorporating a simplified magnetized disk wind model to explain the observed features in DM Tau. Employing multifluid simulations with an embedded medium mass planet, we successfully replicate the gap formation and asymmetric structures evident in ALMA Band 6 and the recent Karl G. Jansky Very Large Array 7 mm observations. Our results suggest that when magnetized disk wind dominates the accretion mode of the system, it is entirely possible for a planet with a medium mass to exist within the gap inside 20 au of DM Tau. This means that DM Tau may not be as turbulent as imagined. However, viscosity within the disk should also contribute a little turbulence to maintain disk stability. [ABSTRACT FROM AUTHOR]

The principal regular satellites of gas giants are thought to be formed by the accumulation of solid materials in circumplanetary disks (CPDs). While there has been significant progress in the study of satellite formation in CPDs, details of the supply of satellite building blocks to CPDs remain unclear. We perform the orbital integration of solid particles in the protoplanetary disk (PPD) approaching a planet, considering the gas drag force by using the results of three-dimensional hydrodynamical simulations of a local region around the planet. We investigate the planetary mass dependence of the capture positions and the capture rates of dust particles accreting onto the CPD. We also examine the degree of dust retention in the accreting gas onto the CPD, which is important for determining the ratio of the dust-to-gas inflow rates, a key parameter in satellite formation. We find that the degree of dust retention increases with increasing planetary mass for a given dust scale height in the PPD. In the case of a small planet (M p = 0.2 M Jup), most particles with insufficient initial altitudes in the PPD are isolated from the gas in the accreting region. On the other hand, in the case of a massive planet (M p = 1 M Jup), dust particles can be coupled to the vertically accreting gas, even when the dust scale height is about 10%–30% of the gas scale height. The results of this study can be used for models of dust delivery and satellite formation in the CPDs of gas giants of various masses, including exoplanets. [ABSTRACT FROM AUTHOR]

The two innermost planets of the Proxima Centauri system are separated by just 0.02 au, inducing strong gravitational interactions between them. We assess this interaction by leveraging fast orbital stability indicators and find that orbital stability is very likely if the initial eccentricities of planets b and d are less than ∼0.2, but cannot confirm stability at larger values. We find that stability is not strongly affected by the true masses of the planets or by the distant planet c. However, mutual inclinations between 95° and 142° often result in unstable motion. We further explore the long-term evolution of the orbits in these stable regions of parameter space and find that circularization can take over 5 Gyr. This tidal evolution could support surface energy fluxes in excess of 1 W m−2 for over 1 Gyr, possibly affecting planet b's habitability. [ABSTRACT FROM AUTHOR]

Fundamental to our understanding of planetary bulk compositions is the relationship between their masses and radii, two properties that are often not simultaneously known for most exoplanets. However, while many previous studies have modeled the two-dimensional relationship between planetary mass and radii, this approach largely ignores the dependencies on other properties that may have influenced the formation and evolution of the planets. In this work, we extend the existing nonparametric and probabilistic framework of MRExo to jointly model distributions beyond two dimensions. Our updated framework can now simultaneously model up to four observables, while also incorporating asymmetric measurement uncertainties and upper limits in the data. We showcase the potential of this multidimensional approach to three science cases: (i) a four-dimensional joint fit to planetary mass, radius, insolation, and stellar mass, hinting of changes in planetary bulk density across insolation and stellar mass; (ii) a three-dimensional fit to the California Kepler Survey sample showing how the planet radius valley evolves across different stellar masses; and (iii) a two-dimensional fit to a sample of Class-II protoplanetary disks in Lupus while incorporating the upper limits in dust mass measurements. In addition, we employ bootstrap and Monte Carlo sampling to quantify the impact of the finite sample size as well as measurement uncertainties on the predicted quantities. We update our existing open-source user-friendly MRExo Python package with these changes, which allows users to apply this highly flexible framework to a variety of data sets beyond what we have shown here. [ABSTRACT FROM AUTHOR]

We use numerical simulations of circumplanetary disks to determine the boundary between disks that are radially truncated by the tidal potential and those where gas escapes the Hill sphere. We consider a model problem, in which a coplanar circumplanetary disk is resupplied with gas at an injection radius smaller than the Hill radius. We evolve the disk using the Phantom smoothed particle hydrodynamics code until a steady state is reached. We find that the most significant dependence of the truncation boundary is on the disk aspect ratio H / R. Circumplanetary disks are efficiently truncated for H / R ≲ 0.2. For H / R ≃ 0.3, up to about half of the injected mass, depending on the injection radius, flows outward through the decretion disk and escapes. As expected from analytic arguments, the conditions (H / R and Shakura–Sunyaev α) required for tidal truncation are independent of planet mass. A simulation with larger α = 0.1 shows stronger outflow than one with α = 0.01, but the dependence on transport efficiency is less important than variations of H / R. Our results suggest two distinct classes of circumplanetary disks: tidally truncated thin disks with dust-poor outer regions, and thicker actively decreting disks with enhanced dust-to-gas ratios. Applying our results to the PDS 70 c system, we predict a largely truncated circumplanetary disk, but it is possible that enough mass escapes to support an outward flow of dust that could explain the observed disk size. [ABSTRACT FROM AUTHOR]

Pebble accretion is recognized as a significant accelerator of planet formation. Yet only formulae for single-sized (monodisperse) distribution have been derived in the literature. These can lead to significant underestimates for Bondi accretion, for which the best accreted pebble size may not be the one that dominates the mass distribution. We derive in this paper the polydisperse theory of pebble accretion. We consider a power-law distribution in pebble radius, and we find the resulting surface and volume number density distribution functions. We derive also the exact monodisperse analytical pebble accretion rate for which 3D accretion and 2D accretion are limits. In addition, we find analytical solutions to the polydisperse 2D Hill and 3D Bondi limits. We integrate the polydisperse pebble accretion numerically for the MRN distribution, finding a slight decrease (by an exact factor 3/7) in the Hill regime compared to the monodisperse case. In contrast, in the Bondi regime, we find accretion rates 1–2 orders of magnitude higher compared to monodisperse, also extending the onset of pebble accretion to 1–2 orders of magnitude lower in mass. We find megayear timescales, within the disk lifetime, for Bondi accretion on top of planetary seeds of masses 10−6 to 10−4 M ⊕, over a significant range of the parameter space. This mass range overlaps with the high-mass end of the planetesimal initial mass function, and thus pebble accretion is possible directly following formation by streaming instability. This alleviates the need for mutual planetesimal collisions as a major contribution to planetary growth. [ABSTRACT FROM AUTHOR]

A major motivation of spectroscopic observations of giant exoplanets is to unveil planet formation processes from atmospheric compositions. Several recent studies suggested that atmospheric nitrogen, like carbon and oxygen, can provide important constraints on planetary formation environments. Since nitrogen chemistry can be far from thermochemical equilibrium in warm atmospheres, we extensively investigate under what conditions, and with what assumptions, the observable NH3 abundances can diagnose an atmosphere's bulk nitrogen abundance. In the first paper of this series, we investigate atmospheric T–P profiles across equilibrium temperature, surface gravity, intrinsic temperature, atmospheric metallicity, and C/O ratio using a 1D radiative–convective equilibrium model. Models with the same intrinsic temperature and surface gravity coincide with a shared "universal" adiabat in the deep atmosphere, across a wide equilibrium temperature range (250–1200 K), which is not seen in hotter or cooler models. We explain this behavior in terms of the classic "radiative zero solution" and then establish a semianalytical T–P profile of the deep atmospheres of warm exoplanets. This profile is then used to predict vertically quenched NH3 abundances. At solar metallicity, our results show that the quenched NH3 abundance only coincides with the bulk nitrogen abundance (within 10%) at low intrinsic temperature, corresponding to a planet with a sub-Jupiter mass (≲1 M J) and old age (≳1 Gyr). If a planet has a high-metallicity (≳10× solar) atmosphere, the quenched NH3 abundance significantly underestimates the bulk nitrogen abundance at almost all planetary masses and ages. We suggest modeling and observational strategies to improve the assessment of bulk nitrogen from NH3. [ABSTRACT FROM AUTHOR]

Rocky planets both in and outside of our solar system are observed to have a range of core-mass fractions (CMFs). Imperfect collisions can preferentially strip mantle material from a planet, changing its CMF, and are therefore thought to be the most likely cause of this observed CMF variation. However, previous work that implements these collisions into N -body simulations of planet formation has struggled to reliably form high CMF super-Earths. In this work, we specify our initial conditions and simulation parameters to maximize the prevalence of high-energy, CMF-changing collisions in order to form planets with highly diverse CMFs. High-energy collisions have a large v imp/ v esc ratio, so we maximize this ratio by starting simulations with high eccentricity and inclination disks to increase the difference in their orbital velocities, maximizing v imp. Additionally, we minimize v esc by starting with small embryos. The final planets undergo more high-energy, debris-producing collisions, and experience significant CMF change over their formation. However, we find that a number of processes work together to average out the CMF of a planet over time; therefore, we do not consistently form high CMF, high-mass planets. We do form high CMF planets below 0.5 M ⊕. Additionally, we find, in these highly eccentric environments, loss of debris mass due to collisional grinding has a significant effect on final planet masses and CMFs, resulting in smaller planets and a higher average planet CMF. This work highlights the importance of improving measurements of high-density planets to better constrain their CMFs. [ABSTRACT FROM AUTHOR]

Free-floating (or rogue) planets are planets that are liberated (or ejected) from their host systems. Although simulations predict their existence in substantial numbers, direct observational evidence for free-floating planets with masses below ∼5 M Jup is still lacking. Several cycle-1 observing programs with JWST aim to hunt for them in four different star-forming clusters. These surveys are designed to be sensitive to masses of 1â€"15 M Jup (assuming a hot-start formation), which corresponds to spectral types of early L to late T for the ages of these clusters. If the existing simulations are not wide off the mark, we show here that the planned programs are likely to find up to 10â€"20 giant rogue planets in moderate density clusters like NGC1333 or IC348, and several dozen to ∼100 in high-density regions like NGC2024 and the Orion Nebula Cluster. These numbers correspond to 1%â€"5% of the total cluster population; they could be substantially higher if stars form multiple giant planets at birth. In contrast, the number of free-floating brown dwarfs, formed from core collapse (like stars) is expected to be significantly lower, only about 0.25% of the number of stars, or 1â€"7 for the clusters considered here. Below 10 M Jup that number drops further by an order of magnitude. We also show that the planned surveys are not at risk of being significantly contaminated by field brown dwarfs in the foreground or background, after spectroscopic confirmation. Taken together, our results imply that if a population of L and T dwarfs were to be found in these JWST surveys, it is expected to be predominantly made up of rogue planets. [ABSTRACT FROM AUTHOR]

It is often assumed that the “Kepler dichotomy”â€"the apparent excess of planetary systems with a single detected transiting planet in the Kepler catalogâ€"reflects an intrinsic bimodality in the mutual inclinations of planetary orbits. After conducting 600 simulations of planet formation followed by simulated Kepler observations, we instead propose that the apparent dichotomy reflects a divergence in the amount of migration and the separation of planetary semimajor axes into distinct “clusters.” We find that our simulated high-mass systems migrate rapidly, bringing more planets into orbital periods of less than 200 days. The outer planets are often caught in a migration trapâ€"a range of planet masses and locations in which a dominant corotation torque prevents inward migrationâ€"which splits the system into two clusters. If clusters are sufficiently separated, the inner cluster remains dynamically cold, leading to low mutual inclinations and a higher probability of detecting multiple transiting planets. Conversely, our simulated low-mass systems typically bring fewer planets within 200 days, forming a single cluster that quickly becomes dynamically unstable, leading to collisions and high mutual inclinations. We propose an alternative explanation for the apparent Kepler dichotomy in which migration traps during formation lead to fewer planets within the Kepler detection window, and where mutual inclinations play only a secondary role. If our scenario is correct, then Kepler’s Systems with Tightly packed Inner Planets are a sample of planets that escaped capture by corotation traps, and their sizes may be a valuable probe into the structure of protoplanetary disks. [ABSTRACT FROM AUTHOR]

Planet-induced substructures, like annular gaps, observed in dust emission from protoplanetary disks, provide a unique probe for characterizing unseen young planets. While deep-learning-based models have an edge in characterizing a planet’s properties over traditional methods, such as customized simulations and empirical relations, they lacks the ability to quantify the uncertainties associated with their predictions. In this paper, we introduce a Bayesian deep-learning network, “DPNNet-Bayesian,” which can predict planet mass from disk gaps and also provides the uncertainties associated with the prediction. A unique feature of our approach is that it is able to distinguish between the uncertainty associated with the deep-learning architecture and the uncertainty inherent in the input data due to measurement noise. The model is trained on a data set generated from diskâ€"planet simulations using the fargo3d hydrodynamics code, with a newly implemented fixed grain size module and improved initial conditions. The Bayesian framework enables the estimation of a gauge/confidence interval over the validity of the prediction, when applied to unknown observations. As a proof of concept, we apply DPNNet-Bayesian to the dust gaps observed in HL Tau. The network predicts masses of 86.0 ± 5.5 M ⊕, 43.8 ± 3.3 M ⊕, and 92.2 ± 5.1 M ⊕, respectively, which are comparable to those from other studies based on specialized simulations. [ABSTRACT FROM AUTHOR]

We detail the follow-up and characterization of a transiting exo-Venus identified by TESS, GJ 3929b (TOI-2013b), and its nontransiting companion planet, GJ 3929c (TOI-2013c). GJ 3929b is an Earth-sized exoplanet in its star’s Venus zone (P b = 2.616272 ± 0.000005 days; S b = 17.3 âˆ' 0.7 + 0.8 S ⊕) orbiting a nearby M dwarf. GJ 3929c is most likely a nontransiting sub-Neptune. Using the new, ultraprecise NEID spectrometer on the WIYN 3.5 m Telescope at Kitt Peak National Observatory, we are able to modify the mass constraints of planet b reported in previous works and consequently improve the significance of the mass measurement to almost 4 σ confidence (M b = 1.75 ± 0.45 M ⊕). We further adjust the orbital period of planet c from its alias at 14.30 ± 0.03 days to the likely true period of 15.04 ± 0.03 days, and we adjust its minimum mass to m sin i = 5.71 ± 0.92 M ⊕. Using the diffuser-assisted ARCTIC imager on the ARC 3.5 m telescope at Apache Point Observatory, in addition to publicly available TESS and LCOGT photometry, we are able to constrain the radius of planet b to R p = 1.09 ± 0.04 R ⊕. GJ 3929b is a top candidate for transmission spectroscopy in its size regime (TSM = 14 ± 4), and future atmospheric studies of GJ 3929b stand to shed light on the nature of small planets orbiting M dwarfs. [ABSTRACT FROM AUTHOR]

Terrestrial planets currently in the habitable zones around M dwarfs likely experienced a long-term runaway-greenhouse condition because of a slow decline in host-star luminosity in its pre-main-sequence phase. Accordingly, they might have lost significant portions of their atmospheres including water vapor at high concentration by hydrodynamic escape induced by the strong stellar X-ray and extreme ultraviolet (XUV) irradiation. However, the atmospheric escape rates remain highly uncertain due partly to a lack of understanding of the effect of radiative cooling in the escape outflows. Here we carry out 1D hydrodynamic escape simulations for an H2â€"H2O atmosphere on a planet with mass of 1 M ⊕ considering radiative and chemical processes to estimate the atmospheric escape rate and follow the atmospheric evolution during the early runaway-greenhouse phase. We find that the atmospheric escape rate decreases with the basal H2O/H2 ratio due to the energy loss by the radiative cooling of H2O and chemical products such as OH and OH+: the escape rate of H2 becomes one order of magnitude smaller when the basal H2O/H2 = 0.1 than that of the pure hydrogen atmosphere. The timescale for H2 escape exceeds the duration of the early runaway-greenhouse phase, depending on the initial atmospheric amount and composition, indicating that H2 and H2O could be left behind after the end of the runaway-greenhouse phase. Our results suggest that temperate and reducing environments with oceans could be formed on some terrestrial planets around M dwarfs. [ABSTRACT FROM AUTHOR]

It has been demonstrated that planets belonging to the same close-in, compact multiple-planet system tend to exhibit a striking degree of uniformity in their sizes. A similar trend has also been found to hold for the masses of such planets, but considerations of such intra-system mass uniformity have generally been limited to statistical samples wherein a majority of systems have constituent planetary mass measurements obtained via analysis of transit timing variations (TTVs). Since systems with strong TTV signals typically lie in or near mean motion resonance, it remains to be seen whether intra-system mass uniformity is still readily emergent for nonresonant systems with non-TTV mass provenance. We thus present in this work a mass uniformity analysis of 17 non-TTV systems with masses measured via radial velocity measurements. Using the Gini index, a common statistic for economic inequality, as our primary metric for uniformity, we find that our sample of 17 non-TTV systems displays intra-system mass uniformity at a level of ∼2.5 σ confidence. We provide additional discussion of possible statistical and astrophysical underpinnings for this result. We also demonstrate the existence of a correlation (r = 0.25) between characteristic solid surface density (Σ0) of the minimum-mass extrasolar nebula and system mass Gini index, suggesting that more-massive disks may generally form systems with more-unequal planetary masses. [ABSTRACT FROM AUTHOR]

Atacama Large Millimeter/submillimeter Array (ALMA) continuum observations of thermal emission from the dust component of protoplanetary disks have revealed an abundance of substructures that may be interpreted as evidence for embedded planets, but planet-driven spiral armsâ€"perhaps one of the most compelling lines of evidenceâ€"have proven comparatively elusive. In this work, we test the capabilities of ALMA to detect the planet-driven spiral signal in continuum emission. Carrying out hydrodynamic simulations and radiative transfer calculations, we present synthetic Band 7 continuum images for a wide range of disk and observing conditions. We show that thermal mass planets at tens of astronomical units typically drive spirals detectable within a few hours of integration time, and the detectable planet mass may be as low as ∼Neptune mass (0.3 M th). The grains probed by ALMA form spirals morphologically identical to the underlying gas spiral. The temperature of the dust spiral is crucial in determining its contrast, and spirals are easier to detect in disks with an adiabatic equation of state and longer cooling times. Resolving the spiral is not necessary for its detection; with the help of residual maps, the optimal beam size is a few times the spiral width at a constant noise level. Finally, we show how the presence of gaps and rings can impair our ability to recognize colocated spirals. Our work demonstrates the planet-finding potential of the current design specification of ALMA, and suggests that observing capability is not the bottleneck in searching for spirals induced by thermal mass planets. [ABSTRACT FROM AUTHOR]

The origin of the Uranian satellite system remains uncertain. The four major satellites have nearly circular, coplanar orbits, and the ratio of the satellite system to planetary mass resembles Jupiter’s satellite system, suggesting the Uranian system was similarly formed within a disk produced by gas coaccretion. However, Uranus is a retrograde rotator with a high obliquity. The satellites orbit in its highly tilted equatorial plane in the same sense as the planet’s retrograde rotation, a configuration that cannot be explained by coaccretion alone. In this work, we investigate the first stages of the coaccretion + giant-impact scenario proposed by Morbidelli et al. (2012) for the origin of the Uranian system. In this model, a satellite system formed by coaccretion is destabilized by a giant impact that tilts the planet. The primordial satellites collide and disrupt, creating an outer debris disk that can reorient to the planet’s new equatorial plane and accrete into Uranus’ four major satellites. The needed reorientation out to distances comparable to outermost Oberon requires that the impact creates an inner disk with ≥1% of Uranus’ mass. We here simulate giant impacts that appropriately tilt the planet and leave the system with an angular momentum comparable to that of the current system. We find that such impacts do not produce inner debris disks massive enough to realign the outer debris disk to the post-impact equatorial plane. Although our results are inconsistent with the apparent requirements of a coaccretion + giant-impact model, we suggest alternatives that merit further exploration. [ABSTRACT FROM AUTHOR]

We report the robust detection of coherent, localized deviations from Keplerian rotation possibly associated with the presence of two giant planets embedded in the disk around HD 163296. The analysis is performed using the discminer channel map modeling framework on 12CO J = 2â€"1 DSHARP data. Not only orbital radius but also azimuth of the planets are retrieved by our technique. One of the candidate planets, detected at R = 94 ± 6 au, Ď• = 50° ± 3° (P94), is near the center of one of the gaps in dust continuum emission and is consistent with a planet mass of 1 M Jup. The other planet, located at R = 261 ± 4 au, Ď• = 57° ± 1° (P261), is in the region where a velocity kink was previously observed in 12CO channel maps. Also, we provide a simultaneous description of the height and temperature of the upper and lower emitting surfaces of the disk and propose the line width as a solid observable to track gas substructure. Using azimuthally averaged line width profiles, we detect gas gaps at R = 38, 88, and 136 au, closely matching the location of their dust and kinematical counterparts. Furthermore, we observe strong azimuthal asymmetries in line widths around the gas gap at R = 88 au, possibly linked to turbulent motions driven by the P94 planet. Our results confirm that the discminer is capable of finding localized, otherwise unseen velocity perturbations thanks to its robust statistical framework, but also that it is well suited for studies of the gas properties and vertical structure of protoplanetary disks. [ABSTRACT FROM AUTHOR]

The interest in the structure of ice-rich planetary bodies, in particular the differentiation between ice and rock, has grown due to the discovery of Kuiper Belt objects and exoplanets. We thus carry out a parameter study for a range of planetary masses M, yielding radii 50 ≲ R ≲ 3000 km, and for rock to ice mass ratios between 0.25 and 4, evolving them for 4.5 Gyr in a cold environment, to obtain the present structure. We use a thermal evolution model that allows for liquid and vapor flow in a porous medium, solving mass and energy conservation equations under hydrostatic equilibrium for a spherical body in orbit around a central star. The model includes the effect of pressure on porosity and on the melting temperature, heating by long-lived radioactive isotopes, and temperature-dependent serpentinization and dehydration. We obtain the boundary in parameter space (size, rock content) between bodies that differentiate, forming a rocky core, and those which remain undifferentiated: small bodies, bodies with a low rock content, and the largest bodies considered, which develop high internal pressures and barely attain the melting temperature. The final differentiated structure comprises a rocky core, an ice-rich mantle, and a thin dense crust below the surface. We obtain and discuss the bulk densityâ€"radius relationship. The effect of a very cold environment is investigated, and we find that at an ambient temperature of ∼20 K, small bodies preserve the ice in amorphous form to the present. [ABSTRACT FROM AUTHOR]

Although it is accepted that perfect-merging is not a realistic outcome of collisions, some researchers state that perfect-merging simulations can still be considered as quantitatively reliable representations of the final stage of terrestrial planet formation. Citing the work of Kokubo & Genda, they argue that the differences between the final planets in simulations with perfect-merging and those where collisions are resolved accurately are small, and it is justified to use perfect-merging results as an acceptable approximation to realistic simulations. In this paper, we show that this argument does not stand. We demonstrate that when the mass lost during collisions is taken into account, the final masses of the planets will be so different from those obtained from perfect-merging that the latter cannot be used as an approximation. We carried out a large number of smooth particle hydrodynamics simulations of embryo–embryo collisions and determined the amount of the mass and water lost in each impact. We applied the results to collisions in a typical perfect-merging simulation and showed that even when the mass loss in each collision is as small as 10%, perfect-merging can, on average, overestimate the masses of the final planets by ∼35% and their water content by more than 18%. Our analysis demonstrates that, while perfect-merging simulations are still a powerful tool in proving concepts, they cannot be used to make predictions, draw quantitative conclusions (especially about the past history of a planetary system), or serve as a valid approximation to the simulations in which collisions are resolved accurately. [ABSTRACT FROM AUTHOR]

Ice-rich planets are formed exterior to the water ice line and thus are expected to contain a substantial amount of ice. The high ice content leads to unique conditions in the interior, under which the structure of a planet is affected by ice interaction with other metals. We apply experimental data of ice–rock interaction at high pressure, and calculate detailed thermal evolution for possible interior configurations of ice-rich planets, in the mass range of super-Earth to Neptunes (5–15 M⊕). We model the effect of migration inward on the ice-rich interior by including the influences of stellar flux and envelope mass loss. We find that ice and rock are expected to remain mixed, due to miscibility at high pressure, in substantial parts of the planetary interior for billions of years. We also find that the deep interior of planetary twins that have migrated to different distances from the star are usually similar, if no mass loss occurs. Significant mass loss results in separation of the water from the rock on the surface and emergence of a volatile atmosphere of less than 1% of the planet's mass. The mass of the atmosphere of water/steam is limited by the ice–rock interaction. We conclude that when ice is abundant in planetary interiors the planet structure may differ significantly from the standard layered structure of a water shell on top of a rocky core. Similar structure is expected in both close-in and further-out planets. [ABSTRACT FROM AUTHOR]

A giant planet embedded in a protoplanetary disk opens a gap by tidal interaction, and properties of the gap strongly depend on the planetary mass and disk parameters. Many numerical simulations of this process have been conducted, but detailed simulations and analysis of gap formation by a super-Jupiter-mass planet have not been thoroughly conducted. We performed two-dimensional numerical hydrodynamic simulations of the gap formation process by a super-Jupiter-mass planet and examined the eccentricity of the gap. When the planet is massive, the radial motion of gas is excited, causing the eccentricity of the gap’s outer edge to increase. Our simulations showed that the critical planetary mass for the eccentric gap was ∼ 3 M J in a disk with α = 4.0 Ă— 10âˆ'3 and h / r = 0.05, a finding that was consistent with that reported in a previous work. The critical planetary mass for the eccentric gap depends on the viscosity and the disk scale height. We found that the critical mass could be described by considering a dimensionless parameter related to the gap depth. The onset of gap eccentricity enhanced the surface density inside the gap, shallowing the gap more than the empirical relation derived in previous studies for a planet heavier than the critical mass. Therefore, our results suggest that the mass accretion rate, which strongly depends on the gas surface density in the gap, is also enhanced for super-Jupiter-mass planets. These results may substantially impact the formation and evolution processes of super-Jupiter-mass planets and population synthesis calculations. [ABSTRACT FROM AUTHOR]

We carried out 3D dust + gas radiative hydrodynamic simulations of forming planets. We investigated a parameter grid of a Neptune-mass, a Saturn-mass, a Jupiter-mass, and a five-Jupiter-mass planet at 5.2, 30, and 50 au distance from their star. We found that the meridional circulation (Szulágyi et al. 2014; Fung & Chiang 2016) drives a strong vertical flow for the dust as well, hence the dust is not settled in the midplane, even for millimeter-sized grains. The meridional circulation will deliver dust and gas vertically onto the circumplanetary region, efficiently bridging over the gap. The Hill-sphere accretion rates for the dust are ∼10âˆ'8â€"10âˆ'10 M Jup yrâˆ'1, increasing with planet mass. For the gas component, the gain is 10âˆ'6â€"10âˆ'8 M Jup yrâˆ'1. The difference between the dust and gas-accretion rates is smaller with decreasing planetary mass. In the vicinity of the planet, the millimeter-sized grains can get trapped easier than the gas, which means the circumplanetary disk might be enriched with solids in comparison to the circumstellar disk. We calculated the local dust-to-gas ratio (DTG) everywhere in the circumstellar disk and identified the altitude above the midplane where the DTG is 1, 0.1, 0.01, and 0.001. The larger the planetary mass, the more the millimeter-sized dust is delivered and a larger fraction of the dust disk is lifted by the planet. The stirring of millimeter-sized dust is negligible for Neptune-mass planets or below, but significant above Saturn-mass planets. [ABSTRACT FROM AUTHOR]

Planets are born from disks of gas and dust, and observations of protoplanetary disks are used to constrain the initial conditions of planet formation. However, dust mass measurements of Class II disks with ALMA have called into question whether they contain enough solids to build the exoplanets that have been detected to date. In this paper, we calculate the mass and spatial scale of solid material around Sun-like stars probed by transit and radial velocity exoplanet surveys and compare those to the observed dust masses and sizes of Class II disks in the same stellar-mass regime. We show that the apparent mass discrepancy disappears when accounting for observational selection and detection biases. We find a discrepancy only when the planet formation efficiency is below 100%, or if there is a population of undetected exoplanets that significantly contributes to the mass in solids. We identify a positive correlation between the masses of planetary systems and their respective orbital periods, which is consistent with the trend between the masses and the outer radii of Class II dust disks. This implies that, despite a factor 100 difference in spatial scale, the properties of protoplanetary disks seem to be imprinted on the exoplanet population. [ABSTRACT FROM AUTHOR]

Ultra-short-period (USP) planets are an enigmatic subset of exoplanets defined by having orbital periods <1 day. It is still not understood how USP planets form, or to what degree they differ from planets with longer orbital periods. Most USP planets have radii <2 R⊕, while planets that orbit further from their star extend to Jupiter size (>10 R⊕). Several theories attempt to explain the formation and composition of USP planets: they could be remnant cores of larger gas giants that lost their atmospheres due to photoevaporation or Roche-lobe overflow, or they could have developed through mass accretion in the innermost part of the protoplanetary disk. The radius and mass distribution of USP planets could provide important clues to distinguish between potential formation mechanisms. In this study, we first verify and update the Kepler catalog of USP planet host star properties, incorporating new data collected by the Gaia mission where applicable. We then use the transit depths measured by Kepler to derive a radius distribution and present occurrence rates for USP planets. Using spherical and tidally distorted planet models, we then derive a mass distribution for USP planets. Comparisons between the updated USP planet mass distribution and simulated planetary systems offer further insights into the formation and evolutionary processes shaping USP planet populations. [ABSTRACT FROM AUTHOR]

A large fraction of known exoplanets have short orbital periods where tidal excitation of gravity waves within the host star causes the planets' orbits to decay. We study the effects of tidal resonance locking, in which the planet locks into resonance with a tidally excited stellar gravity mode. Because a star's gravity mode frequencies typically increase as the star evolves, the planet's orbital frequency increases in lockstep, potentially causing much faster orbital decay than predicted by other tidal theories. Due to nonlinear mode damping, resonance locking in Sun-like stars likely only operates for low-mass planets (M ≲ 0.1 MJup), but in stars with convective cores it can likely operate for all planetary masses. The orbital decay timescale with resonance locking is typically comparable to the star's main-sequence lifetime, corresponding to a wide range in effective stellar quality factor (103 ≲ Q′ ≲ 109), depending on the planet's mass and orbital period. We make predictions for several individual systems and examine the orbital evolution resulting from both resonance locking and nonlinear wave dissipation. Our models demonstrate how short-period massive planets can be quickly destroyed by nonlinear mode damping, while short-period low-mass planets can survive, even though they undergo substantial inward tidal migration via resonance locking. [ABSTRACT FROM AUTHOR]

We present a detailed analysis for a subset of the high-resolution (∼35 mas, or 5 au) ALMA observations from the Disk Substructures at High Angular Resolution Project (DSHARP) to search for faint 1.3 mm continuum emission associated with dusty circumplanetary material located within the narrow annuli of depleted emission (gaps) in circumstellar disks. This search used the Jennings et al. frank modeling methodology to mitigate contamination from the local disk emission and then deployed a suite of injection–recovery experiments to statistically characterize point-like circumplanetary disks in residual images. While there are a few putative candidates in this sample, they have only marginal local signal-to-noise ratios and would require deeper measurements to confirm. Associating a 50% recovery fraction with an upper limit, we find that these data are sensitive to circumplanetary disks with flux densities ≳50–70 μJy in most cases. There are a few examples where those limits are inflated (≳110 μJy) owing to lingering nonaxisymmetric structures in their host circumstellar disks, most notably for a newly identified faint spiral in the HD 143006 disk. For standard assumptions, this analysis suggests that these data should be sensitive to circumplanetary disks with dust masses. While those bounds are comparable to some theoretical expectations for young giant planets, we discuss how plausible system properties (e.g., relatively low host planet masses or the efficient radial drift of solids) could require much deeper observations to achieve robust detections. [ABSTRACT FROM AUTHOR]

We investigate the properties of the hydrodynamic flow around eccentric protoplanets and compare them with the often assumed case of a circular orbit. To this end, we perform a set of 3D hydrodynamic simulations of protoplanets with small eccentricities (e ≤ 0.1). We adopt an isothermal equation of state and concentrate resolution on the protoplanet to investigate flows down to the scale of the protoplanet's circumplanetary disk (CPD). We find enhanced prograde rotation exterior to the CPD for low planet masses undergoing subsonic eccentric motion. If the eccentricity is made large enough to develop a bow shock, this trend reverses and rotation becomes increasingly retrograde. The instantaneous eccentric flow field is dramatically altered compared to circular orbits. Whereas the latter exhibits a generic pattern of polar inflow and midplane outflow, the flow geometry depends on the orbital phase in the eccentric case. For even the modest eccentricities tested here, the dominant source of inflow can come from the midplane instead of the poles. We find that the amount of inflow and outflow increases for higher e and lower protoplanet masses, thereby recycling more gas through the planet's Bondi radius. These increased fluxes may increase the pebble accretion rate for eccentric planets up to several times that of the circular orbit rate. In response to the eccentric motion, the structure and rotation of the planet's bound CPD remain unchanged. Because the CPD regulates the eventual accretion of gas onto the planet, we predict little change to the gas accretion rates between eccentric and circular planets. [ABSTRACT FROM AUTHOR]

We report the discovery of a circumstellar debris disk viewed nearly edge-on and associated with the young, K1 star BD+45° 598 using high-contrast imaging at 2.2 μm obtained at the W.M. Keck Observatory. We detect the disk in scattered light with a peak significance of ∼5σ over three epochs, and our best-fit model of the disk is an almost edge-on ∼70 au ring, with inclination angle ∼87°. Using the NOEMA interferometer at the Plateau de Bure Observatory operating at 1.3 mm, we find resolved continuum emission aligned with the ring structure seen in the 2.2 μm images. We estimate a fractional infrared luminosity of LIR/Ltot × 10−4, higher than that of the debris disk around AU Mic. Several characteristics of BD+45° 598, such as its galactic space motion, placement in a color–magnitude diagram, and strong presence of lithium, are all consistent with its membership in the β Pictoris Moving Group with an age of 23 ± 3 Myr. However, the galactic position for BD+45° 598 is slightly discrepant from previously known members of the β Pictoris Moving Group, possibly indicating an extension of members of this moving group to distances of at least 70 pc. BD+45° 598 appears to be an example from a population of young circumstellar debris systems associated with newly identified members of young moving groups that can be imaged in scattered light, key objects for mapping out the early evolution of planetary systems from ∼10–100 Myr. This target will also be ideal for northern-hemisphere, high-contrast imaging platforms to search for self-luminous, planetary mass companions residing in this system. [ABSTRACT FROM AUTHOR]

We present analytic estimates of the fractional uncertainties on the mass, radius, surface gravity, and density of a transiting planet, using only empirical or semi-empirical measurements. We first express these parameters in terms of transit photometry and radial velocity (RV) observables, as well as the stellar radius R⋆, if required. In agreement with previous results, we find that, assuming a circular orbit, the surface gravity of the planet (gp) depends only on empirical transit and RV parameters, namely the planet period P, the transit depth δ, the RV semi-amplitude K⋆, the transit duration T, and the ingress/egress duration τ. However, the planet mass and density depend on all these quantities, plus R⋆. Thus, an inference about the planet mass, radius, and density must rely upon an external constraint such as the stellar radius. For bright stars, stellar radii can now be measured nearly empirically by using measurements of the stellar bolometric flux, the effective temperature, and the distance to the star via its parallax, with the extinction AV being the only free parameter. For any given system, there is a hierarchy of achievable precisions on the planetary parameters, such that the planetary surface gravity is more accurately measured than the density, which in turn is more accurately measured than the mass. We find that surface gravity provides a strong constraint on the core mass fraction of terrestrial planets. This is useful, given that the surface gravity may be one of the best measured properties of a terrestrial planet. [ABSTRACT FROM AUTHOR]

This paper constructs a theoretical framework for calculating the distribution of masses for gas giant planets forming via the core accretion paradigm. Starting with known properties of circumstellar disks, we present models for the planetary mass distribution over the range 0.1MJ ≤ Mp < 10MJ. If the circumstellar disk lifetime is solely responsible for the end of planetary mass accretion, the observed (nearly) exponential distribution of disk lifetime would imprint an exponential falloff in the planetary mass function. This result is in apparent conflict with observations, which suggest that the mass distribution has a (nearly) power-law form of , with an index of p ≈ 1.3, over the relevant planetary mass range (and for stellar masses ∼0.5–2M⊙). The mass accretion rate onto the planet depends on the fraction of the (circumstellar) disk accretion flow that enters the Hill sphere, and on the efficiency with which the planet captures the incoming material. Models for the planetary mass function that include distributions for these efficiencies, with uninformed priors, can produce nearly power-law behavior, consistent with current observations. The disk lifetimes, accretion rates, and other input parameters depend on the mass of the host star. We show how these variations lead to different forms for the planetary mass function for different stellar masses. Compared to stars with masses M* = 0.5–2M⊙, stars with smaller masses are predicted to have a steeper planetary mass function (fewer large planets). [ABSTRACT FROM AUTHOR]

Close-in gas giants are expected to have a strong magnetic field of ∼10–100 G. Magnetic fields in extrasolar giant planets are detectable by future radio observations in ≳10 MHz and the spectropolarimetry of atomic lines. In contrast, the elusive interiors of exoplanets remain largely unknown. Here we consider the possibility of inferring the existence of the innermost cores of extrasolar giant planets through the detection of planetary magnetic fields. We simulated the long-term thermal evolution of close-in giant planets with masses of 0.2–10 MJup to estimate their magnetic field strengths. A young, massive gas giant tends to have a strong magnetic field. The magnetic field strength of a hot Jupiter is insensitive to its core mass, whereas the core strongly affects the emergence of a planetary dynamo in a hot Saturn. No dynamo-driven magnetic field is generated in a hot Saturn with no core or a small one until ∼10–100 Myr if metallization of hydrogen occurs at ≳1–1.5 Mbar. The magnetic field strength of an evolved gas giant after ∼100 Myr is almost independent of the stellar incident flux. Detecting the magnetic field of a young, hot Saturn as a good indicator of its core may be challenging because of the weakness of radio signals and the shielding effect of plasma in Earth's ionosphere. Hot Jupiters with ≳0.4 MJup can be promising candidates for future ground-based radio observations. [ABSTRACT FROM AUTHOR]

Inferring planetary parameters from transit timing variations (TTVs) is challenging for small exoplanets because their transits may be so weak that determination of individual transit timing is difficult or impossible. We implement a useful combination of tools that together provide a numerically fast global photodynamical model. This is used to fit the TTV-bearing light curve, in order to constrain the masses of transiting exoplanets in low-eccentricity, multiplanet systems—and small planets in particular. We present inferred dynamical masses and orbital eccentricities in four multi-planet systems from Kepler's complete long-cadence data set. We test our model against Kepler-36/KOI-277, a system with some of the most precisely determined planetary masses through TTV inversion methods, and find masses of 5.56+0.41−0.45 and 9.76+0.79−0.89 for Kepler-36 b and c, respectively—consistent with literature in both value and error. We then improve the mass determination of the four planets in Kepler-79/KOI-152, where literature values were physically problematic to 12.5+4.5−3.6, 9.5+2.3−2.1, 11.3+2.2−2.2 and 6.3+1.0−1.0 for Kepler-79 b, c, d, and e, respectively. We provide new mass constraints where none existed before for two systems. These are 12.5+3.2−2.6 for Kepler-450 c, and 3.3+1.7−1.0 and 17.4+7.1−3.8 for Kepler-595 c (previously KOI-547.03) and b, respectively. The photodynamical code used here, called PyDynamicaLC , is made publicly available. [ABSTRACT FROM AUTHOR]

We calculated hydrogen recombination line luminosities (H-α, Paschen-β and Brackett-γ) from 3D thermohydrodynamical simulations of forming planets from 1 to 10 Jupiter mass (MJup). We explored various opacities to estimate the line emissions with extinction, in each case assuming boundary-layer accretion. When realistic opacities are considered, only lines from planets ≥10 MJup can be detected with current instrumentation, highlighting that most planets do not have detectable emission. This might explain the very low detection rate of H-α from forming planets from observations. While the line emission comes from both the forming planet and its circumplanetary disk, we found that only the disk component could be detected due to extinction. We examined the line variability as well, and found that it is higher for higher-mass planets. Furthermore, we determine for the first time the parametric relationship between the mass of the planet and the luminosity of the hydrogen recombination lines, as well as the equation between the accretion luminosity and hydrogen recombination line luminosities. [ABSTRACT FROM AUTHOR]

Chondrules are crystallized droplets of silicate melt formed by rapid heating to high temperatures (>1800 K) of solid precursors followed by hours or days of cooling. The time interval of chondrule formation is consistent with the formation timescale of Jupiter in the core-accretion model (1–4 Myr). Here we investigate if the shocks generated by a massive planet could generate flash heating episodes necessary to form chondrules using high-resolution 2D simulations with the multifluid code RoSSBi. We use different radiative cooling prescriptions, planet masses, orbits, and disk models. Temperatures reached during flash heating can be deduced from chondrule observations and are achieved in a Minimum Mass Solar Nebula (MMSN) for a massive protoplanet (>0.75 M♃) but only in cases in which radiative cooling is low enough to lead to nearly adiabatic conditions. More realistic thermodynamics undershoot the temperatures required in shocks for chondrule formation. However, these temperatures are reached when considering more massive disks (e.g., five MMSN), but these conditions lead to fast planet migration and too low cooling rates compared to those deduced from chondrule textures. Thus, it seems unlikely that shocks from Jupiter can form chondrules in most cases. Independent of the nebular mass, the simulations demonstrate that a massive planet that forms a gap triggers vortices, which act as dust traps for chondrule precursors. These vortices also provide a high-pressure environment consistent with cosmochemical evidence from chondrules. They only lack the flash heating source for a potential chondrule formation environment. [ABSTRACT FROM AUTHOR]

Observations of bright protoplanetary disks often show annular gaps in their dust emission. One interpretation of these gaps is disk–planet interaction. If so, fitting models of planetary gaps to observed protoplanetary disk gaps can reveal the presence of hidden planets. However, future surveys are expected to produce an ever-increasing number of protoplanetary disks with gaps. In this case, performing a customized fitting for each target becomes impractical owing to the complexity of disk–planet interaction. To this end, we introduce Disk Planet Neural Network (DPNNet), an efficient model of planetary gaps by exploiting the power of machine learning. We train a deep neural network with a large number of dusty disk–planet hydrodynamic simulations across a range of planet masses, disk temperatures, disk viscosities, disk surface density profiles, particle Stokes numbers, and dust abundances. The network can then be deployed to extract the planet mass for a given gap morphology. In this work, first in a series, we focus on the basic concepts of our machine learning framework. We demonstrate its utility by applying it to the dust gaps observed in the protoplanetary disk around HL Tau at 10, 30, and 80 au. Our network predicts planet masses of 80 M⊕, 63 M⊕, and 70 M⊕, respectively, which are comparable to those from other studies based on specialized simulations. We discuss the key advantages of our DPNNet in its flexibility to incorporate new physics as well as any number of parameters and predictions, in addition to its potential to ultimately replace hydrodynamical simulations for disk observers and modelers. [ABSTRACT FROM AUTHOR]

During their formation, emerging protoplanets tidally interact with their natal disks. Proto–gas giant planets, with Hill radii larger than the disk thickness, open gaps and quench gas flow in the vicinity of their orbits. It is usually assumed that their type II migration is coupled to the viscous evolution of the disk. Although this hypothesis provides an explanation for the origin of close-in planets, it also encounters a predicament on the retention of long-period orbits for most gas giant planets. Moreover, numerical simulations indicate that the planets' migrations are not solely determined by the viscous diffusion of their natal disk. Here we carry out a series of hydrodynamic simulations combined with analytic studies to examine the transition between different paradigms of type II migration. We find a range of planetary mass for which gas continues to flow through a severely depleted gap so that the surface density distribution in the disk region beyond the gap is maintained in a quasi-steady state. The associated gap profile modifies the location of corotation and Lindblad resonances. In the proximity of the planet's orbit, high-order Lindblad and corotation torque are weakened by the gas depletion in the gap, while low-order Lindblad torques near the gap walls preserve their magnitude. Consequently, the intrinsic surface density distribution of the disk delicately determines both the pace and direction of the planets' type II migration. We show that this effect might stall the inward migration of giant planets and preserve them in disk regions where the surface density is steep. [ABSTRACT FROM AUTHOR]

Much recent work on planet formation has focused on the growth of planets by accretion of grains whose aerodynamic properties make them marginally coupled to the nebular gas, a theory commonly referred to as "pebble accretion." While the rapid growth rates of pebble accretion can ameliorate some problems in planet formation theory, they raise new concerns as well. A particular issue is the preponderance of observed planets that end their growth as "super-Earths" or "sub-Neptunes," with masses in the range 2–10 M⊕. Once planets reach this mass scale, growth by pebble accretion is so rapid that ubiquitously ending growth at super-Earth masses is difficult unless growth rates drop at this mass scale. In this work, we highlight this issue in detail using our previously published model of pebble accretion, and also propose a reason for this change in growth rate: feedback between the growing planet's atmosphere and the gas disk inhibits accretion of smaller particle sizes by forcing them to flow around the growing planet instead of being accreted. For reasonable fiducial disk parameters, this "flow isolation" will inhibit accretion of all available particle sizes once the planet reaches super-Earth masses. We also demonstrate that the characteristics of this "flow isolation mass" agree with previously published trends identified in the Kepler planets. [ABSTRACT FROM AUTHOR]

The population of exoplanetary systems detected by Kepler provides opportunities to refine our understanding of planet formation. Unraveling the conditions needed to produce the observed exoplanet systems will allow us to make informed predictions as to where habitable worlds exist within the galaxy. In this paper, we examine, using N-body simulations, how the properties of planetary systems are determined during the final stages of assembly, when planets accrete from embryos and planetesimals. While accretion is a chaotic process, trends emerge allowing certain features of an ensemble of planetary systems to provide a memory of the initial distribution of solid mass around a star prior to accretion. We also use epos , the Exoplanet Population Observation Simulator, to account for detection biases and show that different accretion scenarios can be distinguished from observations of the Kepler systems. We show that the period of the innermost planet, the ratio of orbital periods of adjacent planets, and masses of the planets are determined by the total mass and radial distribution of embryos and planetesimals at the beginning of accretion. In general, some amount of orbital damping, via either planetesimals or gas, during accretion is needed to match the whole population of exoplanets. Surprisingly, all simulated planetary systems have planets that are similar in size, showing that the "peas in a pod" pattern can be consistent with both a giant impact scenario and a planet migration scenario. The inclusion of material at distances larger than what Kepler observes (>1 au) has a profound impact on the observed planetary architectures and thus on the formation and delivery of volatiles to possible habitable worlds. [ABSTRACT FROM AUTHOR]

While the solar system contains no planets between the sizes of Uranus and Saturn, our current exoplanet census includes several dozen such planets with well-measured masses and radii. These sub-Saturns exhibit a diversity of bulk densities, ranging from ∼0.1 to 3 g cm−3. When modeled simply as hydrogen/helium envelopes atop rocky cores, this diversity in densities translates to a diversity in planetary envelope fractions, fenv = Menv/Mp, ranging from ∼10% to ∼50%. Planets with fenv ≈ 50% pose a challenge to traditional models of giant planet formation by core-nucleated accretion, which predict the onset of runaway gas accretion when Menv ∼ Mcore. Here, we show that many of these apparent fenv ≈ 50% planets are less envelope-rich than they seem, after accounting for tidal heating. We present a new framework for modeling sub-Saturn interiors that incorporates envelope inflation due to tides, which are driven by the observed nonzero eccentricities, as well as potential obliquities. Consequently, when we apply our models to known sub-Saturns, we infer lower fenv than tides-free estimates. We present a case study of K2-19 b, a moderately eccentric sub-Saturn. Neglecting tides, K2-19 b appears to have fenv ≈ 50%, poised precariously near the runaway threshold; by including tides, however, we find fenv ≈ 10%, resolving the tension. Through a systematic analysis of 4–8 R⊕ planets, we find that most (but not all) of the similarly envelope-rich planets have more modest envelopes of fenv ≈ 10%–20%. Thus, many sub-Saturns may be understood as sub-Neptunes that have undergone significant radius inflation, rather than a separate class of objects. Tidally induced radius inflation likely plays an important role in other size classes of planets including ultra-low-density Jupiter-size planets like WASP-107 b. [ABSTRACT FROM AUTHOR]

We define a second-order moment of the observational differential microlensing curves that can be used to impose constraints on physical properties of lensed quasars. We show that this quantity is sensitive both to variations in the source size and the deflector mass. We formulize a methodology to recover the source size from the observational measurements when the mass spectrum is fixed. As a case study, we test it with a sample of four quadruple lenses, both in simulated scenarios and with real data from the Chandra X-ray Observatory. In our simulations with a uniform stellar population the method works best to detect sources around 0.1 Einstein radii, giving correct upper/lower limits for much smaller/bigger sizes without requiring a big leap in additional computational effort as compared to a single-epoch approach, yet taking advantage of multi-epoch information. We apply the method to a small sample of X-ray data from four objects assuming a range of star masses, and obtain a degeneracy relation between the source size and deflector mass. Combined with previous estimates for the size of the X-ray corona, the degeneracy relation suggests that X-ray microlensing is mainly induced by planetary mass objects. [ABSTRACT FROM AUTHOR]

In current models used to interpret exoplanet atmospheric observations, the planetary mass is treated as a prior and is measured/estimated independently with external methods, such as radial velocity or transit timing variation techniques. This approach is necessary as available spectroscopic data do not have sufficient wavelength coverage and/or signal-to-noise to infer the planetary mass. We examine here whether the planetary mass can be directly retrieved from transit spectra as observed by future space observatories, which will provide higher quality spectra. More in general, we quantify the impact of mass uncertainties on spectral retrieval analyses for a host of atmospheric scenarios. Our approach is both analytical and numerical: we first use simple approximations to extract analytically the influence of each atmospheric/planetary parameter to the wavelength-dependent transit depth. We then adopt a fully Bayesian retrieval model to quantify the propagation of the mass uncertainty onto other atmospheric parameters. We found that for clear-sky, gaseous atmospheres the posterior distributions are the same when the mass is known or retrieved. The retrieved mass is very accurate, with a precision of more than 10%, provided the wavelength coverage and signal-to-noise ratio are adequate. When opaque clouds are included in the simulations, the uncertainties in the retrieved mass increase, especially for high altitude clouds. However, atmospheric parameters such as the temperature and trace-gas abundances are unaffected by the knowledge of the mass. Secondary atmospheres, expected to be present in many super-Earths, are more challenging due to the higher degree of freedom for the atmospheric main component, which is unknown. For broad wavelength range and adequate signal-to-noise observations, the mass can still be retrieved accurately and precisely if clouds are not present, and so are all the other atmospheric/planetary parameters. When clouds are added, we find that the mass uncertainties may impact substantially the retrieval of the mean molecular weight: an independent characterization of the mass would therefore be helpful to capture/confirm the main atmospheric constituent. [ABSTRACT FROM AUTHOR]

We utilize the ability of the Hubble Space Telescope to probe near-infrared water absorption present in the atmosphere of low-mass stars and brown-dwarf and planetary-mass objects to create a pure sample of Orion Nebula Cluster (ONC) members, not affected by contamination from background stars and galaxies that lack water absorption. Thanks to these data, we infer the Initial Mass Function (IMF) of the ONC in the 0.005–1.4M⊙ regime (i.e., down to a few Jupiter masses). The young age of the ONC, ∼1 Myr, provides a snapshot of the outcome of star formation for the present-day conditions (metallicity, temperature, pressure) of typical Milky Way disk molecular clouds. We demonstrate that the IMF of the ONC is well described by either a log-normal function or a broken power law, with parameter values qualitatively in agreement with the canonical Chabrier or Kroupa forms for the Milky Way disk IMF. This continuity in the mass distribution provides clues to the fact that the same physical processes may be regulating the formation of stars, brown dwarfs, and planetary-mass objects. Both the canonical IMF forms underpredict the observed number of very-low-mass members (below 0.1 M⊙), a regime where our data allows more precise constraints. Nevertheless, we do not observe a rise or secondary peak in the brown dwarfs or planetary-mass regimes. Our study thus contradicts findings based on broadband near-infrared ground-based photometry, which predict an extremely high number of free-floating planets, but likely suffer from unaccounted background contamination. [ABSTRACT FROM AUTHOR]

The most widely studied mechanism of mass loss from extrasolar planets is photoevaporation via X-ray and ultraviolet ionization, primarily in the context of highly irradiated planets. However, the extreme ultraviolet dissociation of hydrogen molecules can also theoretically drive atmospheric evaporation on low-mass planets. For temperate planets such as the early Earth, impact erosion is expected to dominate in the traditional planetesimal accretion model, but it would be greatly reduced in pebble accretion scenarios, allowing other mass-loss processes to be major contributors. We apply the same prescription for photoionization to this photodissociation mechanism and compare it to an analysis of other possible sources of mass loss in pebble accretion scenarios. We find that there is no clear path to evaporating the primordial atmosphere accreted by an early Earth analog in a pebble accretion scenario. Impact erosion could remove ∼2300 bars of hydrogen if 1% of the planet's mass is accreted as planetesimals, while the combined photoevaporation processes could evaporate ∼750 bars of hydrogen. Photodissociation is likely a subdominant but significant component of mass loss. Similar results apply to super-Earths and mini-Neptunes. This mechanism could also preferentially remove hydrogen from a planet's primordial atmosphere, thereby leaving a larger abundance of primordial water compared to standard dry formation models. We discuss the implications of these results for models of rocky planet formation, including Earth's formation, and the possible application of this analysis to mass loss from observed exoplanets. [ABSTRACT FROM AUTHOR]

Recent work suggests that many short-period super-Earth and sub-Neptune planets may have significant spin axis tilts ("obliquities"). When planets are locked in high-obliquity states, the tidal dissipation rate may increase by several orders of magnitude. This intensified heat deposition within the planets' interiors should generate significant structural consequences, including atmospheric inflation leading to larger transit radii. Using up-to-date radius estimates from Gaia Data Release 2, we show evidence for ∼50% larger average radii of planets wide of first-order mean-motion resonances, a population of planets with a theorized frequent occurrence of high obliquities. We investigate whether this radius trend could be a signature of obliquity tides. Using an adaptation of the Modules for Experiments in Stellar Astrophysics (MESA) stellar evolution toolkit, we model the atmospheric evolution of sub-Neptune-mass planets in response to additional internal heat from obliquity tides. The degree of radius inflation predicted by the models is ∼10%–100% for tidal luminosities ≳10−5 of the incident stellar power; this degree of inflation is broadly consistent with the observations and can approximately be described by power-law relationships. We present a few case studies of very low density "super-puff" planets—Kepler-79 d, Kepler-31 c, and Kepler-27 b—and show that they are strong candidates for potentially having undergone tidally induced radius inflation. We also discuss how the discrepancy between the two populations of planets with masses derived from radial velocities and transit timing variations is connected to the radius distribution features we have identified. Altogether, the calculations in this work confirm that tidal dissipation has nonnegligible consequences for the structural properties of short-period sub-Neptunes. [ABSTRACT FROM AUTHOR]

The resonant perturbations from planets are able to halt the drag-induced migration, and capture the inwardly drifting planetesimals into mean motion resonances. The equilibrium eccentricity of planetesimals in resonances, and the minimum size of planetesimal that can trigger resonance trapping, have been analyzed and formulated. However, the analytical works based on the assumption that the disk is axisymmetric, which is violated by the asymmetric structures developed by planets. We perform long-term 2D hydrodynamic simulations to study the dynamics of planetesimals in the j: (j + 1) first-order exterior resonances, and reexamine the theoretical expressions. We find the expression of equilibrium eccentricity underestimates the values for resonances with j < 5, in particular the 1:2 resonance that the underestimation can be 30%–40%. Within the parameter space we explored, we find the equilibrium eccentricity and the minimum size are reduced in an asymmetric disk. The amount of discrepancy in eccentricity depends on the degree of asymmetric structures. For cases of Earth-sized planets, where the disk is less disturbed, the planetesimal's eccentricity can reach to the values predicted by our modified expression. For gaseous planets, however, the eccentricity can be 0.01–0.02 smaller in value. We find the minimum size is 10 times smaller, and the factor seems to be independent of the planet's mass. The influences of asymmetric profiles on the eccentricity and the minimum size could affect the outcome of collisions between resonant and nonresonant planetesimals, and the amount of planetesimals migrated into the planet's feeding zone. [ABSTRACT FROM AUTHOR]

We apply our 3D debris disk model, SMACK, to simulate a planet on a circular orbit near a ring of planetesimals that are experiencing destructive collisions. Previous simulations of a planet opening a gap in a collisionless debris disk have found that the width of the gap scales as the planet mass to the 2/7th power (α = 2/7). We find that gap sizes in a collisional disk still obey a power law scaling with planet mass, but that the index a of the power law depends on the age of the system t relative to the collisional timescale tcoll of the disk by α = 0.32(t/tcoll)-0.04, with inferred planet masses up to five times smaller than those predicted by the classical gap law. The increased gap sizes likely stem from the interaction between collisions and the mean motion resonances near the chaotic zone. We investigate the effects of the initial eccentricity distribution of the disk particles and find a negligible effect on the gap size at Jovian planet masses, since collisions tend to erase memory of the initial particle eccentricity distributions. Finally, we find that the presence of Trojan analogs is a potentially powerful diagnostic of planets in the mass range ~ 1-10 MJup. We apply our model to place new upper limits on planets around Fomalhaut, HR 4796 A, HD 202628, HD 181327, and β Pictoris. [ABSTRACT FROM AUTHOR]

We present the BANYAN All-Sky Survey (BASS) catalog, consisting of 228 new late-type (M4-L6) candidate members of nearby young moving groups (YMGs) with an expected false-positive rate of ~13%. This sample includes 79 new candidate young brown dwarfs and 22 planetary-mass objects. These candidates were identified through the first systematic all-sky survey for late-type low-mass stars and brown dwarfs in YMGs. We cross-matched the Two Micron All Sky Survey and AllWISE catalogs outside of the galactic plane to build a sample of 98,970 potential ≥M5 dwarfs in the solar neighborhood and calculated their proper motions with typical precisions of 5-15 mas yr-1. We selected highly probable candidate members of several YMGs from this sample using the Bayesian Analysis for Nearby Young AssociatioNs II tool (BANYAN II). We used the most probable statistical distances inferred from BANYAN II to estimate the spectral type and mass of these candidate YMG members. We used this unique sample to show tentative signs of mass segregation in the AB Doradus moving group and the Tucana-Horologium and Columba associations. The BASS sample has already been successful in identifying several new young brown dwarfs in earlier publications, and will be of great interest in studying the initial mass function of YMGs and for the search of exoplanets by direct imaging; the input sample of potential close-by ≥M5 dwarfs will be useful to study the kinematics of low-mass stars and brown dwarfs and search for new proper motion pairs. [ABSTRACT FROM AUTHOR]

We present multiwavelength photometry, high angular resolution imaging, and radial velocities of the unique and confounding disintegrating low-mass planet candidate KIC 12557548b. Our high angular resolution imaging, which includes space-based Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) observations in the optical (∼0.53 μm and ∼0.77 μm), and ground-based Keck/NIRC2 observations in K′ band (∼2.12 μm), allow us to rule out background and foreground candidates at angular separations greater than 0.″2 that are bright enough to be responsible for the transits we associate with KIC 12557548. Our radial velocity limit from Keck/HIRES allows us to rule out bound, low-mass stellar companions (∼0.2 M☼) to KIC 12557548 on orbits less than 10 yr, as well as placing an upper limit on the mass of the candidate planet of 1.2 Jupiter masses; therefore, the combination of our radial velocities, high angular resolution imaging, and photometry are able to rule out most false positive interpretations of the transits. Our precise multiwavelength photometry includes two simultaneous detections of the transit of KIC 12557548b using Canada-France-Hawaii Telescope/Wide-field InfraRed Camera (CFHT/WIRCam) at 2.15 μm and the Kepler space telescope at 0.6 μm, as well as simultaneous null-detections of the transit by Kepler and HST/WFC3 at 1.4 μm. Our simultaneous HST/WFC3 and Kepler null-detections provide no evidence for radically different transit depths at these wavelengths. Our simultaneous CFHT/WIRCam detections in the near-infrared and with Kepler in the optical reveal very similar transit depths (the average ratio of the transit depths at ∼2.15 μm compared with ∼0.6 μm is: 1.02 ± 0.20). This suggests that if the transits we observe are due to scattering from single-size particles streaming from the planet in a comet-like tail, then the particles must be ∼0.5 μm in radius or larger, which would favor that KIC 12557548b is a sub-Mercury rather than super-Mercury mass planet. [ABSTRACT FROM AUTHOR]

We present the first microlensing candidate for a free-floating exoplanet-exomoon system, MOA-2011-BLG-262, with a primary lens mass of Mhost ∼ 4 Jupiter masses hosting a sub-Earth mass moon. The argument for an exomoon hinges on the system being relatively close to the Sun. The data constrain the product MLπrel where ML is the lens system mass and πrel is the lens-source relative parallax. If the lens system is nearby (large πrel), then ML is small (a few Jupiter masses) and the companion is a sub-Earth-mass exomoon. The best-fit solution has a large lens-source relative proper motion, μrel = 19.6 ± 1.6 mas yr–1, which would rule out a distant lens system unless the source star has an unusually high proper motion. However, data from the OGLE collaboration nearly rule out a high source proper motion, so the exoplanet+exomoon model is the favored interpretation for the best fit model. However, there is an alternate solution that has a lower proper motion and fits the data almost as well. This solution is compatible with a distant (so stellar) host. A Bayesian analysis does not favor the exoplanet+exomoon interpretation, so Occam's razor favors a lens system in the bulge with host and companion masses of and , at a projected separation of AU. The existence of this degeneracy is an unlucky accident, so current microlensing experiments are in principle sensitive to exomoons. In some circumstances, it will be possible to definitively establish the mass of such lens systems through the microlensing parallax effect. Future experiments will be sensitive to less extreme exomoons. [ABSTRACT FROM AUTHOR]