Neptune-like Planets Research Articles

Characterisation of the warm-Jupiter TOI-1130 system with CHEOPS and a photo-dynamical approach

Context. Among the thousands of exoplanets discovered to date, approximately a few hundred gas giants on short-period orbits are classified as ‘lonely’ and only a few are in a multi-planet system with a smaller companion on a close orbit. The processes that formed multi-planet systems hosting gas giants on close orbits are poorly understood, and only a few examples of this kind of system have been observed and well characterised. Aims. Within the contest of a multi-planet system hosting a gas giant on short orbits, we characterise the TOI-1130 system by measuring masses and orbital parameters. This is a two-transiting planet system with a Jupiter-like planet (c) on a 8.35 days orbit and a Neptune-like planet (b) on an inner (4.07 days) orbit. Both planets show strong anti-correlated transit timing variations (TTVs). Furthermore, radial velocity (RV) analysis showed an additional linear trend, a possible hint of a non-transiting candidate planet on a far outer orbit. Methods. Since 2019, extensive transit and radial velocity observations of the TOI-1130 have been acquired using TESS and various ground-based facilities. We present a new photo-dynamical analysis of all available transit and RV data, with the addition of new CHEOPS and ASTEP+ data, which achieve the best precision to date on the planetary radii and masses and on the timings of each transit. Results. We were able to model interior structure of planet b constraining the presence of a gaseous envelope of H/He, while it was not possible to assess the possible water content. Furthermore, we analysed the resonant state of the two transiting planets, and we found that they lie just outside the resonant region. This could be the result of the tidal evolution that the system underwent. We obtained both masses of the planets with a precision of less than 1.5%, and radii with a precision of about 1% and 3% for planet b and c, respectively.

Connections between Planetary Populations and Chemical Characteristics of Their Host Stars

Chemical anomalies in planet-hosting stars (PHSs) are studied in order to assess how the planetary nature and multiplicity affect the atmospheric chemical abundances of their host stars. We employ APOGEE DR17 to select thin-disk stars of the Milky Way, and crossmatch them with the Kepler Input Catalog to identify confirmed PHSs, which results in 227 PHSs with available chemical abundance ratios for six refractory elements. We also examine an ensemble of stars without planet signals, which are equivalent to the selected PHSs in terms of evolutionary stage and stellar parameters, to correct for Galactic chemical evolution effects, and derive the abundance gradient of refractory elements over the condensation temperature for the PHSs. Using the Galactic chemical evolution corrected abundances, we find that our PHSs do not show a significant difference in abundance slope from the stars without planets. However, when we examine the trends of the refractory elements of PHSs, based on the total number of their planets and their planet types, we find that the PHSs with giant planets are more depleted in refractory elements than those with rocky planets. Among the PHSs with rocky planets, the refractory depletion trends are potentially correlated with the terrestrial planets’ radii and multiplicity. In the cases of PHSs with giant planets, sub-Jovian PHSs demonstrate more depleted refractory trends than stars hosting Jovian-mass planets, raising questions on different planetary formation processes for Neptune-like and Jupiter-like planets.

How planets grow by pebble accretion

The characterization of super-Earth- to Neptune-sized exoplanets relies heavily on our understanding of their formation and evolution. In this study, we link a model of planet formation by pebble accretion to the planets’ long-term observational properties by calculating the interior evolution, starting from the dissipation of the protoplanetary disk. We investigate the evolution of the interior structure in 5–20 M⊕ planets, accounting for silicate redistribution caused by convective mixing, rainout (condensation and settling), and mass loss. Specifically, we have followed the fate of the hot silicate vapor that remained in the planet’s envelope after planet formation as the planet cools. We find that disk dissipation is followed by a rapid contraction of the envelope from the Hill or Bondi radius to about one-tenth of that size within 10 Myr. Subsequent cooling leads to substantial growth of the planetary core through silicate rainout accompanied by inflated radii, in comparison to the standard models of planets that formed with core-envelope structure. We examined the dependence of rainout on the planet’s envelope mass, on the distance from its host star, on its silicate mass, and on the atmospheric opacity. We find that the population of planets that formed with polluted envelopes can be roughly divided into three groups based on the mass of their gas envelopes: bare rocky cores that have shed their envelopes, super-Earth planets with a core-envelope structure, and Neptune-like planets with diluted cores that undergo gradual rainout. For polluted planets that formed with envelope masses below 0.4 M⊕, we anticipate that the inflation of the planet’s radius caused by rainout will enhance the mass loss by a factor of 2–8 compared to planets with unpolluted envelopes. Our model bridges the gap between the predicted composition gradients in massive planets and the core-envelope structure in smaller planets.

A 3D picture of moist-convection inhibition in hydrogen-rich atmospheres: Implications for K2-18 b

While small Neptune-like planets are among the most abundant exoplanets, our understanding of their atmospheric structure and dynamics remains sparse. In particular, many unknowns remain regarding the way moist convection works in these atmospheres, where condensable species are heavier than the non-condensable background gas. While it has been predicted that moist convection could cease above some threshold abundance of these condensable species, this prediction is based on simple linear analysis and relies on some strong assumptions regarding the saturation of the atmosphere. To investigate this issue, we developed a 3D cloud-resolving model for hydrogen-dominated atmospheres with large amounts of condensable species and applied it to a prototypical temperate Neptune-like planet – K2-18 b. Our model confirms the inhibition of moist convection above a critical abundance of condensable vapor and the onset of a stably stratified layer in the atmosphere of such planets, which leads to much hotter deep atmospheres and interiors. Our 3D simulations further provide quantitative estimates of the turbulent mixing in this stable layer, which is a key driver of the cycling of condensables in the atmosphere. This allowed us to build a very simple, yet realistic, 1D model that captures the most salient features of the structure of Neptune-like atmospheres. Our qualitative findings on the behavior of moist convection in hydrogen atmospheres go beyond temperate planets and should also apply to regions where iron and silicates condense in the deep interior of hydrogen-dominated planets. Finally, we used our model to investigate the likelihood of a liquid ocean beneath an H2-dominated atmosphere on K2-18 b. We find that the planet would need to have a very high albedo (A > 0.5–0.6) to sustain a liquid ocean. However, due to the spectral type of the star, the amount of aerosol scattering that would be needed to provide such a high albedo is inconsistent with the latest observational data.

Precise photoionisation treatment and hydrodynamic effects in atmospheric modelling of warm and hot Neptunes

Context. Observational breakthroughs in the field of exoplanets in the last decade have motivated the development of numerous theoretical models, such as those describing atmospheres and mass loss, which is believed to be one of the main drivers of planetary evolution. Aims. We outline for which types of close-in planets in the Neptune-mass range the accurate treatment of photoionisation effects is most relevant, particularly with respect to atmospheric mass loss and the parameters relevant for interpreting observations, such as temperature and ion fraction. Methods. We developed the Cloudy e Hydro Ancora INsieme (CHAIN) model, which combines our 1D hydrodynamic upper atmosphere model with the non-local thermodynamical equilibrium (NLTE) photoionisation and radiative transfer code Cloudy accounting for ionisation, dissociation, detailed atomic level populations, and chemical reactions for all chemical elements up to zinc. The hydro-dynamic code is responsible for describing the outflow, while Cloudy solves the photoionisation and heating of planetary atmospheres. We applied CHAIN to model the upper atmospheres of a range of Neptune-like planets with masses between 1 and 50 M⊕, also varying the orbital parameters. Results. For the majority of warm and hot Neptunes, we find slower and denser outflows, with lower ion fractions, compared to the predictions of the hydrodynamic model alone. Furthermore, we find significantly different temperature profiles between CHAIN and the hydrodynamic model alone, though the peak values are similar for similar atmospheric compositions. The mass-loss rates predicted by CHAIN are higher for hot strongly irradiated planets and lower for more moderate planets. All differences between the two models are strongly correlated with the amount of high-energy irradiation. Finally, we find that the hydrodynamic effects significantly impact ionisation and heating. Conclusions. The impact of the precise photoionisation treatment provided by Cloudy strongly depends on the system parameters. This suggests that some of the simplifications typically employed in hydrodynamic modelling might lead to systematic errors when studying planetary atmospheres, even at a population-wide level.

Self-gravity of debris discs can strongly change the outcomes of interactions with inclined planets

ABSTRACT Drastic changes in protoplanets’ orbits could occur in the early stages of planetary systems through interactions with other planets and their surrounding protoplanetary or debris discs. The resulting planetary system could exhibit orbits with moderate to high eccentricities and/or inclinations, causing planets to perturb one another as well as the disc significantly. The present work studies the evolution of systems composed of an initially inclined planet and a debris disc. We perform N-body simulations of a narrow, self-gravitating debris disc, and a single interior Neptune-like planet. We simulate systems with various initial planetary inclinations, from coplanar to polar configurations considering different separations between the planet and the disc. We find that except when the planet is initially on a polar orbit, the planet–disc system tends to reach a quasi-coplanar configuration with low vertical dispersion in the disc. When present, the Zeipel–Kozai–Lidov oscillations induced by the disc pump the planet’s eccentricity and, in turn, affect the disc structure. We also find that the resulting disc morphology in most of the simulations looks very similar in both radial and vertical directions once the simulations are converged. This contrasts strongly with massless disc simulations, where vertical disc dispersion is set by the initial disc-planet inclination and can be high for initially highly inclined planets. The results suggest caution in interpreting an unseen planet’s dynamical history based only on the disc’s appearance.

VaTEST. II. Statistical Validation of 11 TESS-detected Exoplanets Orbiting K-type Stars

NASA’s Transiting Exoplanet Survey Satellite (TESS) is an all-sky survey mission designed to find transiting exoplanets orbiting nearby bright stars. It has identified more than 329 transiting exoplanets, and almost 6000 candidates remain unvalidated. In this manuscript, we discuss the findings from the ongoing Validation of Transiting Exoplanets using Statistical Tools (VaTEST) project, which aims to validate new exoplanets for further characterization. We validated 11 new exoplanets by examining the light curves of 24 candidates using the LATTE and TESS-Plot tools and computing the false-positive probabilities using the statistical validation tool TRICERATOPS. These include planets suitable for atmospheric characterization using transmission spectroscopy (TOI-2194b), emission spectroscopy (TOI-3082b and TOI-5704b) and for both transmission and emission spectroscopy (TOI-672b, TOI-1694b, and TOI-2443b). Our validated planets have one super-Earth (TOI-2194b) orbiting a bright (V = 8.42 mag), metal-poor ([Fe/H] = −0.3720 ± 0.1) star, and one short-period Neptune-like planet (TOI-5704) in the hot-Neptune desert. In total, we validated one super-Earth, seven sub-Neptunes, one Neptune-like, and two sub-Saturn or super-Neptune-like exoplanets. Additionally, we identify five likely planet candidates (TOI-323, TOI-1180, TOI-2200, TOI-2408, and TOI-3913), which can be further studied to establish their planetary nature.

The TESS–Keck Survey. XIII. An Eccentric Hot Neptune with a Similar-mass Outer Companion around TOI-1272

We report the discovery of an eccentric hot Neptune and a non-transiting outer planet around TOI-1272. We identified the eccentricity of the inner planet, with an orbital period of 3.3 days and R p,b = 4.1 ± 0.2 R ⊕, based on a mismatch between the observed transit duration and the expected duration for a circular orbit. Using ground-based radial velocity (RV) measurements from the HIRES instrument at the Keck Observatory, we measured the mass of TOI-1272b to be M p,b = 25 ± 2 M ⊕. We also confirmed a high eccentricity of e b = 0.34 ± 0.06, placing TOI-1272b among the most eccentric well-characterized sub-Jovians. We used these RV measurements to also identify a non-transiting outer companion on an 8.7 day orbit with a similar mass of M p,c sin i = 27 ± 3 M ⊕ and e c ≲ 0.35. Dynamically stable planet–planet interactions have likely allowed TOI-1272b to avoid tidal eccentricity decay despite the short circularization timescale expected for a close-in eccentric Neptune. TOI-1272b also maintains an envelope mass fraction of f env ≈ 11% despite its high equilibrium temperature, implying that it may currently be undergoing photoevaporation. This planet joins a small population of short-period Neptune-like planets within the “Hot Neptune Desert” with a poorly understood formation pathway.

Architecture of Planetary Systems Predicted from Protoplanetary Disks Observed with ALMA. II. Evolution Outcomes and Dynamical Stability

Recent ALMA observations on disk substructures suggest the presence of embedded protoplanets in a large number of disks. The primordial configurations of these planetary systems can be deduced from the morphology of the disk substructure and serve as initial conditions for numerical investigation of their future evolution. Starting from the initial configurations of 12 multiplanetary systems deduced from ALMA disks, we carried out two-stage N-body simulation to investigate the evolution of the planetary systems at the disk stage, as well as the long-term orbital stability after the disk dispersal. At the disk stage, our simulation includes both the orbital migration and pebble/gas accretion effects. We found that a variety of planetary systems are produced and can be categorized into distant giant planets, Jupiter-like planets, Neptune-like planets, and distant small planets. We found that the disk-stage evolution and the final configurations are sensitive to both the initial mass assignments and viscosity. After the disk stage, we implement only mutual gravity between star and planets and introduce stochastic perturbative forces. All systems are integrated for up to 10 Gyr to test their orbital stability. Most planetary systems are found to be stable for at least 10 Gyr, with perturbative force in a reasonable range. Our result implies that a strong perturbation source such as stellar flybys is required to drive the planetary system unstable. We discuss the implications of our results on both the disk and planet observation, which may be confirmed by the next-generation telescopes such as JWST and ngVLA.

Substructures in Protoplanetary Disks Imprinted by Compact Planetary Systems

The substructures observed in protoplanetary disks may be the signposts of embedded planets carving gaps or creating vortices. The inferred masses of these planets often fall in the Jovian regime despite their low abundance compared to lower-mass planets, partly because previous works often assume that a single substructure (a gap or vortex) is caused by a single planet. In this work, we study the possible imprints of compact systems composed of Neptune-like planets (∼10–30 M ⊕) and show that long-standing vortices are a prevalent outcome when their interplanetary separation (Δa) falls below ∼8 times H p—the average disk’s scale height at the planet’s locations. In simulations where a single planet is unable to produce long-lived vortices, two-planet systems can preserve them for at least 5000 orbits in two regimes: (i) fully shared density gaps with elongated vortices around the stable Lagrange points L 4 and L 5 for the most compact planet pairs (Δa ≲ 4.6 H p), and (ii) partially shared gaps for more widely spaced planets (Δa ∼ 4.6–8 H p) forming vortices in a density ring between the planets through the Rossby wave instability. The latter case can produce vortices with a wide range of aspect ratios down to ∼3 and can occur for planets captured into the 3:2 (2:1) mean-motion resonances for disks’ aspects ratios of h ≳ 0.033 (h ≳ 0.057). We suggest that their long lifetimes are sustained by the interaction of spiral density waves launched by the neighboring planets. Overall, our results show that the distinguishing imprint of compact systems with Neptune-mass planets are long-lived vortices inside the density gaps, which in turn are shallower than single-planet gaps for a fixed gap width.

Confirmation of the Long-period Planet Orbiting Gliese 411 and the Detection of a New Planet Candidate

We perform a detailed characterization of the planetary system orbiting the bright, nearby M dwarf Gliese 411 using radial velocities gathered by APF, HIRES, SOPHIE, and CARMENES. We confirm the presence of a signal with a period near 2900 days that has been disputed as either a planet or a long-period stellar magnetic cycle. An analysis of activity metrics including the H α and indices supports the interpretation that the signal corresponds to a Neptune-like planet, GJ 411 c. An additional signal near 215 days was previously dismissed as an instrumental systematic, but we find that a planetary origin cannot be ruled out. With a semimajor axis of 0.5142 ± 0.0042 au, this candidate’s orbit falls between those of its companions and is located beyond the outer edge of the system’s habitable zone (determined using the moist greenhouse and maximum greenhouse limits in Kopparapu et al. 2013). It has a minimum mass of 3.89 ± 0.84 M ⊕, giving a radial-velocity amplitude of 0.81 ± 0.18 m s−1. If confirmed, this would be one of the lowest-amplitude planet detections from any of these four instruments. Our analysis of the joint radial-velocity data set also provides tighter constraints on the orbital parameters for the previously known planets. Photometric data from TESS do not show any signs of a transit event. However, the outermost planet and candidate are prime targets for future direct imaging missions, and GJ 411 c may be detectable via astrometry.

Thermal evolution of Uranus and Neptune

Thermal evolution models suggest that the luminosities of both Uranus and Neptune are inconsistent with the classical assumption of an adiabatic interior. Such models commonly predict Uranus to be brighter and, recently, Neptune to be fainter than observed. In this work, we investigate the influence of a thermally conductive boundary layer on the evolution of Uranus- and Neptune-like planets. This thermal boundary layer (TBL) is assumed to be located deep in the planet and be caused by a steep compositional gradient between a H–He-dominated outer envelope and an ice-rich inner envelope. We investigate the effect of TBL thickness, thermal conductivity, and the time of TBL formation on the planet’s cooling behaviour. The calculations were performed with our recently developed tool based on the Henyey method for stellar evolution. We make use of state-of-the-art equations of state for hydrogen, helium, and water, as well as of thermal conductivity data for water calculated via ab initio methods. We find that even a thin conductive layer of a few kilometres has a significant influence on the planetary cooling. In our models, Uranus’ measured luminosity can only be reproduced if the planet has been near equilibrium with the solar incident flux for an extended period of time. For Neptune, we find a range of solutions with a near constant effective temperature at layer thicknesses of 15 km or larger, similar to Uranus. In addition, we find solutions for thin TBLs of a few km and strongly enhanced thermal conductivity. A ~ 1 Gyr later onset of the TBL reduces the present ΔTby an order of magnitude to only several 100 K. Our models suggest that a TBL can significantly influence the present planetary luminosity in both directions, making it appear either brighter or fainter than the adiabatic case.

Production of warm dense water in the laboratory using intense ion beams at FAIR: Application to planetary physics

This paper presents two-dimensional hydrodynamic simulations of implosion of a water sample, which is enclosed in a cylindrical shell of tungsten that is driven by an intense uranium beam. The considered beam parameters match the characteristics of the beam which will be delivered by the heavy ion synchrotron, SIS100, at the Facility for Antiprotons and Ion Research (FAIR). An experimental scheme based on this concept, which is named LAPLAS, is an important part of the high energy density physics research program at FAIR. The simulations show that the LAPLAS implosion leads to a low-entropy compression of water, which generates core conditions of water-rich planets. The importance of this work is underscored by the fact that more than 30% of the discovered extrasolar planets are Neptune-like water-rich planets. To be able to construct a reliable physical model of the formation and evolution of these planets, it is important to have correct understanding of the equation of state of the exotic states of water that exist in the planetary interior. It is thus expected that the knowledge obtained from the LAPLAS experiments will be a very valuable contribution to the field of planetary physics. We show that x-ray radiographic imaging using a high-intensity laser-driven hard x-ray source would be a suitable diagnostic capable of delivering high-resolution images of the hydrodynamic evolution.

The CARMENES search for exoplanets around M dwarfs

We report the discovery of a Neptune-like planet (LP 714-47 b, P = 4.05204 d, mb = 30.8 ± 1.5M⊕, Rb = 4.7 ± 0.3 R⊕) located in the “hot Neptune desert”. Confirmation of the TESS Object of Interest (TOI 442.01) was achieved with radial-velocity follow-up using CARMENES, ESPRESSO, HIRES, iSHELL, and PFS, as well as from photometric data using TESS, Spitzer, and ground-based photometry from MuSCAT2, TRAPPIST-South, MONET-South, the George Mason University telescope, the Las Cumbres Observatory Global Telescope network, the El Sauce telescope, the TÜBİTAK National Observatory, the University of Louisville Manner Telescope, and WASP-South. We also present high-spatial resolution adaptive optics imaging with the Gemini Near-Infrared Imager. The low uncertainties in the mass and radius determination place LP 714-47 b among physically well-characterised planets, allowing for a meaningful comparison with planet structure models. The host star LP 714-47 is a slowly rotating early M dwarf (Teff = 3950 ± 51 K) with a mass of 0.59 ± 0.02M⊙ and a radius of 0.58 ± 0.02R⊙. From long-term photometric monitoring and spectroscopic activity indicators, we determine a stellar rotation period of about 33 d. The stellar activity is also manifested as correlated noise in the radial-velocity data. In the power spectrum of the radial-velocity data, we detect a second signal with a period of 16 days in addition to the four-day signal of the planet. This could be shown to be a harmonic of the stellar rotation period or the signal of a second planet. It may be possible to tell the difference once more TESS data and radial-velocity data are obtained.

Connecting planet formation and astrochemistry

The chemical composition of planetary atmospheres has long been thought to store information regarding where and when a planet accretes its material. Predicting this chemical composition theoretically is a crucial step in linking observational studies to the underlying physics that govern planet formation. As a follow-up to an earlier study of ours on hot Jupiters, we present a population of warm Jupiters (semi-major axis between 0.5 and 4 AU) extracted from the same planetesimal formation population synthesis model as used in that previous work. We compute the astrochemical evolution of the proto-planetary disks included in this population to predict the carbon-to-oxygen (C/O) and nitrogen-to-oxygen (N/O) ratio evolution of the disk gas, ice, and refractory sources, the accretion of which greatly impacts the resulting C/Os and N/Os in the atmosphere of giant planets. We confirm that the main sequence (between accreted solid mass and the atmospheric C/O) we found previously is largely reproduced by the presented population of synthetic warm Jupiters. As a result, the majority of the population falls along the empirically derived mass-metallicity relation when the natal disk has solar or lower metallicity. Planets forming from disks with high metallicity ([Fe/H] > 0.1) results in more scatter in chemical properties, which could explain some of the scatter found in the mass-metallicity relation. Combining predicted C/Os and N/Os shows that Jupiter does not fall among our population of synthetic planets, suggesting that it likely did not form in the inner 5 AU of the Solar System before proceeding into a Grand Tack. This result is consistent with a recent analysis of the chemical composition of Jupiter’s atmosphere, which suggests that it accreted most of its heavy element abundance farther than tens of AU away from the Sun. Finally, we explore the impact of different carbon refractory erosion models, including the location of the carbon erosion front. Shifting the erosion front has a major impact on the resulting C/Os of Jupiter- and Neptune-like planets, but warm Saturns see a smaller shift in C/Os since their carbon and oxygen abundances are equally impacted by gas and refractory accretion.

Zodiacal exoplanets in time – XI. The orbit and radiation environment of the young M dwarf-hosted planet K2-25b

ABSTRACT M dwarf stars are high-priority targets for searches for Earth-size and potentially Earth-like planets, but their planetary systems may form and evolve in very different circumstellar environments than those of solar-type stars. To explore the evolution of these systems, we obtained transit spectroscopy and photometry of the Neptune-size planet orbiting the ≈650-Myr-old Hyades M dwarf K2-25. An analysis of the variation in spectral line shape induced by the Doppler ‘shadow’ of the planet indicates that the planet’s orbit is closely aligned with the stellar equator ($\lambda =-1.7_{-3.7}^{+5.8}$ deg), and that an eccentric orbit found by previous work could arise from perturbations by another planet on a coplanar orbit. We detect no significant variation in the depth of the He i line at 1083 nm during transit. A model of atmospheric escape as an isothermal Parker wind with a solar composition shows that this non-detection is not constraining compared to escape rate predictions of ∼0.1 M⊕ Gyr−1; at such rates, at least several Gyr are required for a Neptune-like planet to evolve into a rocky super-Earth.

Tidal evolution of exoplanetary systems hosting potentially habitable exoplanets. The cases of LHS-1140 b-c and K2-18 b-c

ABSTRACT We present a model to study secularly and tidally evolving three-body systems composed by two low-mass planets orbiting a star, in the case where the bodies rotation axes are always perpendicular to the orbital plane. The tidal theory allows us to study the spin and orbit evolution of both stiff Earth-like planets and predominantly gaseous Neptune-like planets. The model is applied to study two recently discovered exoplanetary systems containing potentially habitable exoplanets (PHE): LHS-1140 b-c and K2-18 b-c. For the former system, we show that both LHS-1140 b and c must be in nearly circular orbits. For K2-18 b-c, the combined analysis of orbital evolution time-scales with the current eccentricity estimation of K2-18 b allows us to conclude that the inner planet (K2-18 c) must be a Neptune-like gaseous body. Only this would allow for the eccentricity of K2-18 b to be in the range of values estimated in recent works (e = 0.20 ± 0.08), provided that the uniform viscosity coefficient of K2-18 b is greater than 2.4 × 1019 Pa s (which is a value characteristic of stiff bodies) and supposing that such system has an age of some Gyr.

TOI-132 b: A short-period planet in the Neptune desert transiting a V = 11.3 G-type star★

ABSTRACT The Neptune desert is a feature seen in the radius-period plane, whereby a notable dearth of short period, Neptune-like planets is found. Here, we report the Transiting Exoplanet Survey Satellite (TESS) discovery of a new short-period planet in the Neptune desert, orbiting the G-type dwarf TYC 8003-1117-1 (TOI-132). TESS photometry shows transit-like dips at the level of ∼1400 ppm occurring every ∼2.11 d. High-precision radial velocity follow-up with High Accuracy Radial Velocity Planet Searcher confirmed the planetary nature of the transit signal and provided a semi-amplitude radial velocity variation of 11.38 $^{+0.84}_{-0.85}$ m s−1, which, when combined with the stellar mass of 0.97 ± 0.06 M⊙, provides a planetary mass of 22.40$^{+1.90}_{-1.92}$ M⊕. Modelling the TESS light curve returns a planet radius of 3.42$^{+0.13}_{-0.14}$ R⊕, and therefore the planet bulk density is found to be 3.08$^{+0.44}_{-0.46}$ g cm−3. Planet structure models suggest that the bulk of the planet mass is in the form of a rocky core, with an atmospheric mass fraction of 4.3$^{+1.2}_{-2.3}$ per cent. TOI-132 b is a TESS Level 1 Science Requirement candidate, and therefore priority follow-up will allow the search for additional planets in the system, whilst helping to constrain low-mass planet formation and evolution models, particularly valuable for better understanding of the Neptune desert.

Search for Nearby Earth Analogs. II. Detection of Five New Planets, Eight Planet Candidates, and Confirmation of Three Planets around Nine Nearby M Dwarfs*

Abstract Zechmeister et al. surveyed 38 nearby M dwarfs from 2000 to 2007 March with VLT2 and the Ultraviolet and Visual Echelle Spectrograph (UVES) spectrometer. These data have recently been reanalyzed, yielding a significant improvement in the Doppler velocity precision. Spurred by this, we have combined the UVES data with velocity sets from High Accuracy Radial velocity Planet Searcher, Magellan/Planet Finder Spectrograph, and Keck/High Resolution Echelle Spectrometer. Sixteen planet candidates have been uncovered orbiting nine M dwarfs. Five of them are new planets corresponding to radial velocity signals, which are not sensitive to the choice of noise models and are identified in multiple data sets over various time spans. Eight candidate planets require additional observation to be confirmed. We also confirm three previously reported planets. Among the new planets, GJ 180 d and GJ 229A c are super-Earths located in the conservative habitable zones of their host stars. We investigate their dynamical stability using the Monte Carlo approach and find both planetary orbits are robust to the gravitational perturbations of the companion planets. Due to their proximity to the Sun, the angular separation between the host stars and the potentially habitable planets in these two systems is 25 and 59 mas, respectively. They are thus good candidates for future direct imaging by James Webb Space Telescope and E-ELT. In addition, we find GJ 433 c, a cold super-Neptune belonging to an unexplored population of Neptune-like planets. With a separation of 0.″5 from its host star, GJ 433 c is probably the first realistic candidate for the direct imaging of cold Neptunes. A comprehensive survey of these planets is important for the studies of planet formation.

The Escape of the Hydrogen-rich Atmosphere of Exoplanets: Mass-loss Rates and the Absorption of Stellar Lyα

Abstract Because mass-loss rates are the function of the mean density of a planet and the stellar irradiation, we calculated about 450 models covering planets with different densities and stellar irradiation. Our results show that the mass-loss rates are dependent on the stellar irradiation and the mean density. However, the mass-loss rates predicted by the energy-limited equation are higher than those predicted by the hydrodynamic model when the integrated extreme ultraviolet flux is higher than ∼2 × 104 erg cm−2 s−1. The overestimation can be revised if the kinetic and thermal energies of the escaping atmosphere is included in the energy-limited equation. We found that the heating efficiencies are proportional to the product of the gravitational potential of the planet and the stellar irradiation. The mean absorption radii of stellar irradiation are 1.1–1.2 R p for Jupiter-like planets, while they vary in the range of 1.1–1.7 R p for planets with smaller sizes. We evaluated the absorption of stellar Lyα by the planetary atmosphere and found that the deeper Lyα absorptions tend to be located in the high stellar irradiation and low planetary mean density regions, and vice versa. Moreover, planets with mass-loss rates higher than 1011 g s−1 are likely to exhibit obvious absorptions. Finally, we suggest that the absorption levels are related to the inherent properties of exoplanets. The planets with larger sizes (or lower mean density) show strong Lyα absorptions. Neptune-like and Earth-like planets tend to have weak Lyα absorptions because of their small sizes (or high densities).