Neptune-mass Planet Research Articles

Formation of Close-in Neptunes around Low-mass Stars through Breaking Resonant Chains

Conventional planet formation theories predict a paucity of massive planets around small stars, especially very low-mass (0.1−0.3 M ⊙) mid-to-late M dwarfs. Such tiny stars are expected to form planets of terrestrial sizes but not much bigger. However, this expectation is challenged by the recent discovery of LHS 3154 b, a planet with period of 3.7 days and minimum mass of 13.2 M ⊕ orbiting a 0.11 M ⊙ star. Here, we propose that close-in Neptune-mass planets like LHS 3154 b formed through an anomalous series of mergers from a primordial compact system of super-Earths. We perform simulations within the context of the “breaking the chains” scenario, in which super-Earths initially form in tightly spaced chains of mean-motion resonances before experiencing dynamical instabilities and collisions. Planets as massive and close-in as LHS 3154 b (M p ∼ 12−20 M ⊕, P < 7 days) are produced in ∼1% of simulated systems, in broad agreement with their low observed occurrence. These results suggest that such planets do not require particularly unusual formation conditions but rather are an occasional by-product of a process that is already theorized to explain compact multiplanet systems. Interestingly, our simulated systems with LHS 3154 b-like planets also contain smaller planets at around ∼30 days, offering a possible test of this hypothesis.

The CARMENES search for exoplanets around M dwarfs. Revisiting the GJ 581 multi-planetary system with new Doppler measurements from CARMENES, HARPS, and HIRES

GJ\,581 is a nearby M dwarf known to host a packed multiple planet system composed of two super-Earths and a Neptune-mass planet. We present new orbital analyses of the GJ\,581 system, utilizing recent radial velocity (RV) data obtained from the CARMENES spectrograph combined with newly reprocessed archival data from the HARPS and HIRES spectrographs. Our aim was to analyze the post-discovery spectroscopic data of GJ\,581, which were obtained with CARMENES. In addition, we used publicly available HIRES and HARPS spectroscopic data to seek evidence of the known and disputed exoplanets in this system. We aimed to investigate the stellar activity of GJ\,581 and update the planetary system's orbital parameters using state-of-the-art numerical models and techniques. We performed a periodogram analysis of the available precise CARMENES, HIRES, and HARPS RVs and of stellar activity indicators. We conducted detailed orbital analyses by testing various orbital configurations consistent with the RV data. We studied the posterior probability distribution of the parameters fit to the data and we explored the long-term stability and overall orbital dynamics of the GJ\,581 system. We refined the orbital parameters of the GJ\,581 system using the most precise and complete set of Doppler data available. Consistent with the existing literature, our analysis confirms that the system is unequivocally composed of only three planets detectable in the present data, dismissing the putative planet GJ\,581\,d as an artifact of stellar activity. Our N-body fit reveals that the system's inclination is $i = $\,deg, which implies that the planets could be up to 30&lt;!PCT!&gt; more massive than their previously reported minimum masses. Furthermore, we report that the GJ\,581 system exhibits long-term stability, as indicated by the posterior probability distribution, characterized by secular dynamical interactions without the involvement of mean motion resonances.

Astrometric detection of a Neptune-mass candidate planet in the nearest M-dwarf binary system GJ65 with VLTI/GRAVITY

The detection of low-mass planets orbiting the nearest stars is a central stake of exoplanetary science, as they can be directly characterized much more easily than their distant counterparts. Here, we present the results of our long-term astrometric observations of the nearest binary M-dwarf Gliese 65 AB (GJ65), located at a distance of only 2.67 pc. We monitored the relative astrometry of the two components from 2016 to 2023 with the VLTI/GRAVITY interferometric instrument. We derived highly accurate orbital parameters for the stellar system, along with the dynamical masses of the two red dwarfs. The GRAVITY measurements exhibit a mean accuracy per epoch of 50−60 ms in 1.5 h of observing time using the 1.8 m Auxiliary Telescopes. The residuals of the two-body orbital fit enable us to search for the presence of companions orbiting one of the two stars (S-type orbit) through the reflex motion they imprint on the differential A–B astrometry. We detected a Neptune-mass candidate companion with an orbital period of p = 156 ± 1 d and a mass of mp = 36 ± 7 M⊕. The best-fit orbit is within the dynamical stability region of the stellar pair. It has a low eccentricity, e = 0.1 − 0.3, and the planetary orbit plane has a moderate-to-high inclination of i &gt; 30° with respect to the stellar pair, with further observations required to confirm these values. These observations demonstrate the capability of interferometric astrometry to reach microarcsecond accuracy in the narrow-angle regime for planet detection by reflex motion from the ground. This capability offers new perspectives and potential synergies with Gaia in the pursuit of low-mass exoplanets in the solar neighborhood.

OGLE-2017-BLG-0448Lb: A Low Mass–Ratio Wide-orbit Microlensing Planet?

The gravitational microlensing technique is most sensitive to planets in a Jupiter-like orbit and has detected more than 200 planets. However, only a few wide-orbit (s > 2) microlensing planets have been discovered, where s is the planet-to-host separation normalized to the angular Einstein ring radius, θ E. Here, we present the discovery and analysis of a strong candidate wide-orbit microlensing planet in the event OGLE-2017-BLG-0448. The whole light curve exhibits long-term residuals to the static binary-lens single-source model, so we investigate the residuals by adding the microlensing parallax, microlensing xallarap, an additional lens, or an additional source. For the first time, we observe a complex degeneracy between all four effects. The wide-orbit models with s ∼ 2.5 and a planet-to-host mass ratio of q ∼ 10−4 are significantly preferred, but we cannot rule out the close models with s ∼ 0.35 and q ∼ 10−3. A Bayesian analysis based on a Galactic model indicates that, despite the complicated degeneracy, the surviving wide-orbit models all contain a super-Earth-mass to Neptune-mass planet at a projected planet-host separation of ∼6 au and the surviving close-orbit models all consist of a Jovian-mass planet at ∼1 au. The host star is probably an M or K dwarf. We discuss the implications of this dimension-degeneracy disaster on microlensing light-curve analysis and its potential impact on statistical studies.

Free-floating or Wide-orbit? Keck Adaptive-optics Observations of Free-floating Planet Candidates Detected with Gravitational Microlensing

Recent detections of extremely short-timescale microlensing events imply the existence of a large population of Earth- to Neptune-mass planets that appear to have no host stars. However, it is currently unknown whether these objects are truly free-floating planets or whether they are in wide orbits around a distant host star. Here, we present an analysis of high-resolution imaging observations of five free-floating planet candidates collected with the Keck telescope. If these candidates were actually wide-orbit planets, then the light of the host would appear at a separation of 40–60 mas from the microlensing source star. No such stars are detected. We carry out injection and recovery simulations to estimate the sensitivity to putative host stars at different separations. Depending on the object, the presented observations rule out 11%–36% of potential hosts assuming that the probability of hosting a planet does not depend on the host mass. The results are sensitive to the latter assumption, and the probability of detecting the host star in the analyzed images may be a factor of 1.9 ± 0.1 larger, if the exoplanet hosting probability scales as the first power of the host star mass, as suggested by recent studies of planetary microlensing events. We argue that deeper observations, for example with JWST, are needed to confidently confirm or refute the free-floating planet hypothesis.

A Neptune-mass exoplanet in close orbit around a very low-mass star challenges formation models.

Theories of planet formation predict that low-mass stars should rarely host exoplanets with masses exceeding that of Neptune. We used radial velocity observations to detect a Neptune-mass exoplanet orbiting LHS 3154, a star that is nine times less massive than the Sun. The exoplanet's orbital period is 3.7 days, and its minimum mass is 13.2 Earth masses. We used simulations to show that the high planet-to-star mass ratio (>3.5 × 10-4) is not an expected outcome of either the core accretion or gravitational instability theories of planet formation. In the core-accretion simulations, we show that close-in Neptune-mass planets are only formed if the dust mass of the protoplanetary disk is an order of magnitude greater than typically observed around very low-mass stars.

A Wolf 359 in Sheep's Clothing: Hunting for Substellar Companions in the Fifth-closest System Using Combined High-contrast Imaging and Radial Velocity Analysis

Wolf 359 (CN Leo, GJ 406, Gaia DR3 3864972938605115520) is a low-mass star in the fifth-closest neighboring system (2.41 pc). Because of its relative youth and proximity, Wolf 359 offers a unique opportunity to study substellar companions around M stars using infrared high-contrast imaging and radial velocity monitoring. We present the results of Ms-band (4.67 μm) vector vortex coronagraphic imaging using Keck-NIRC2 and add 12 Keck-HIRES and 68 MAROON-X velocities to the radial velocity baseline. Our analysis incorporates these data alongside literature radial velocities from CARMENES, the High Accuracy Radial velocity Planet Searcher, and Keck-HIRES to rule out the existence of a close (a < 10 au) stellar or brown dwarf companion and the majority of large gas giant companions. Our survey does not refute or confirm the long-period radial velocity candidate, Wolf 359 b (P ∼ 2900 days), but rules out the candidate's existence as a large gas giant (>4 M Jup) assuming an age of younger than 1 Gyr. We discuss the performance of our high-contrast imaging survey to aid future observers using Keck-NIRC2 in conjunction with the vortex coronagraph in the Ms band and conclude by exploring the direct imaging capabilities with JWST to observe Jupiter- and Neptune-mass planets around Wolf 359.

Revisiting the Transit Timing and Atmosphere Characterization of the Neptune-mass Planet HAT-P-26 b

We present a transit-timing variation (TTV) and planetary atmosphere analysis of the Neptune-mass planet HAT-P-26 b. We present a new set of 13 transit light curves from optical ground-based observations and combine them with light curves from the Wide Field Camera 3 on the Hubble Space Telescope, the Transiting Exoplanet Survey Satellite, and previously published ground-based data. We refine the planetary parameters of HAT-P-26 b and undertake a TTV analysis using 33 transits obtained over seven years. The TTV analysis shows an amplitude signal of 1.98 ± 0.05 minutes, which could result from the presence of an additional ∼0.02 M Jup planet at a 1:2 mean-motion resonance orbit. Using a combination of transit depths spanning optical to near-infrared wavelengths, we find that the atmosphere of HAT-P-26 b contains % H2O with a derived temperature of K.

Terrestrial- and Neptune-mass Free-Floating Planet Candidates from the MOA-II 9 yr Galactic Bulge Survey

We report the discoveries of low-mass free-floating planet (FFP) candidates from the analysis of 2006–2014 MOA-II Galactic bulge survey data. In this data set, we found 6111 microlensing candidates and identified a statistical sample consisting of 3535 high-quality single-lens events with Einstein radius crossing times in the range 0.057 < t E/days < 757, including 13 events that show clear finite-source effects with angular Einstein radii of 0.90 < θ E/μas < 332.54. Two of the 12 events with t E < 1 day have significant finite-source effects, and one event, MOA-9y-5919, with t E = 0.057 ± 0.016 days and θ E = 0.90 ± 0.14 μas, is the second terrestrial-mass FFP candidate to date. A Bayesian analysis indicates a lens mass of M ⊕ for this event. The low detection efficiency for short-duration events implies a large population of low-mass FFPs. The microlensing detection efficiency for low-mass planet events depends on both the Einstein radius crossing times and the angular Einstein radii, so we have used image-level simulations to determine the detection efficiency dependence on both t E and θ E. This allows us to use a Galactic model to simulate the t E and θ E distribution of events produced by the known stellar populations and models of the FFP distribution that are fit to the data. Methods like this will be needed for the more precise FFP demographics determinations from Nancy Grace Roman Space Telescope data.

Discovery and characterization of two Neptune-mass planets orbiting HD 212729 with TESS

ABSTRACT We report the discovery of two exoplanets orbiting around HD 212729 (TOI 1052, TIC 317060587), a Teff = 6146 K star with V = 9.51 observed by TESS in Sectors 1 and 13. One exoplanet, TOI-1052b, is Neptune-mass and transits the star, and an additional planet TOI-1052c is observed in radial velocities but not seen to transit. We confirm the planetary nature of TOI-1052b using precise radial velocity observations from HARPS and determined its parameters in a joint RV and photometry analysis. TOI-1052b has a radius of $2.87^{+0.29}_{-0.24}$ R⊕, a mass of 16.9 ± 1.7 M⊕, and an orbital period of 9.14 d. TOI-1052c does not show any transits in the TESS data, and has a minimum mass of $34.3^{+4.1}_{-3.7}$ M⊕ and an orbital period of 35.8 d, placing it just interior to the 4:1 mean-motion resonance. Both planets are best fit by relatively high but only marginally significant eccentricities of $0.18^{+0.09}_{-0.07}$ for planet b and $0.24^{+0.09}_{-0.08}$ for planet c. We perform a dynamical analysis and internal structure model of the planets as well as deriving stellar parameters and chemical abundances. The mean density of TOI-1052b is $3.9^{+1.7}_{-1.3}$ g cm−3 consistent with an internal structure similar to Neptune. A nearby star is observed in Gaia DR3 with the same distance and proper motion as TOI-1052, at a sky projected separation of $\scriptstyle \sim$1500 au, making this a potential wide binary star system.

TOI-179: A young system with a transiting compact Neptune-mass planet and a low-mass companion in outer orbit

Context. Transiting planets around young stars are key benchmarks for our understanding of planetary systems. One such candidate, TOI-179, was identified around the K dwarf HD 18599 by TESS. Aims. We present the confirmation of the transiting planet and the characterization of the host star and of the TOI-179 system over a broad range of angular separations. Methods. We exploited the TESS photometric time series, intensive radial velocity monitoring performed with HARPS, and deep high-contrast imaging observations obtained with SPHERE and NACO at VLT. The inclusion of Gaussian process regression analysis was effective to properly model the magnetic activity of the star and identify the Keplerian signature of the transiting planet. Results. The star, with an age of 400±100 Myr, is orbited by a transiting planet with period 4.137436 days, mass 24±7 M⊕, radius 2.62−0.12+0.15 R⊕, and significant eccentricity (0.34−0.09+0.07). Adaptive optics observations identified a low-mass companion at the boundary between brown dwarfs and very low-mass stars (mass derived from luminosity 83−6+4 MJ) at a very small projected separation (84.5 mas, 3.3 au at the distance of the star). Coupling the imaging detection with the long-term radial velocity trend and the astrometric signature, we constrained the orbit of the low-mass companion, identifying two families of possible orbital solutions. Conclusions. The TOI-179 system represents a high-merit laboratory for our understanding of the physical evolution of planets and other low-mass objects and of how the planet properties are influenced by dynamical effects and interactions with the parent star.

TOI-5678b: A 48-day transiting Neptune-mass planet characterized with CHEOPS and HARPS

Context. A large sample of long-period giant planets has been discovered thanks to long-term radial velocity surveys, but only a few dozen of these planets have a precise radius measurement. Transiting gas giants are crucial targets for the study of atmospheric composition across a wide range of equilibrium temperatures and, more importantly, for shedding light on the formation and evolution of planetary systems. Indeed, compared to hot Jupiters, the atmospheric properties and orbital parameters of cooler gas giants are unaltered by intense stellar irradiation and tidal effects. Aims. We aim to identify long-period planets in the Transiting Exoplanet Survey Satellite (TESS) data as single or duo-transit events. Our goal is to solve the orbital periods of TESS duo-transit candidates with the use of additional space-based photometric observations and to collect follow-up spectroscopic observations in order to confirm the planetary nature and measure the mass of the candidates. Methods. We use the CHaracterising ExOPlanet Satellite (CHEOPS) to observe the highest-probability period aliases in order to discard or confirm a transit event at a given period. Once a period is confirmed, we jointly model the TESS and CHEOPS light curves along with the radial velocity datasets to measure the orbital parameters of the system and obtain precise mass and radius measurements. Results. We report the discovery of a long-period transiting Neptune-mass planet orbiting the G7-type star TOI-5678. Our spectroscopic analysis shows that TOI-5678 is a star with a solar metallicity. The TESS light curve of TOI-5678 presents two transit events separated by almost two years. In addition, CHEOPS observed the target as part of its Guaranteed Time Observation program. After four non-detections corresponding to possible periods, CHEOPS detected a transit event matching a unique period alias. Follow-up radial velocity observations were carried out with the ground-based high-resolution spectrographs CORALIE and HARPS. Joint modeling reveals that TOI-5678 hosts a 47.73 day period planet, and we measure an orbital eccentricity consistent with zero at 2σ. The planet TOI-5678 b has a mass of 20 ± 4 Earth masses (M⊕) and a radius of 4.91 ± 0.08 R⊕ Using interior structure modeling, we find that TOI-5678 b is composed of a low-mass core surrounded by a large H/He layer with a mass of 3.2±1.7−1.3 M⊕. Conclusions. TOI-5678 b is part of a growing sample of well-characterized transiting gas giants receiving moderate amounts of stellar insolation (11 S⊕). Precise density measurement gives us insight into their interior composition, and the objects orbiting bright stars are suitable targets to study the atmospheric composition of cooler gas giants.

Transit Depth Variations Reveal TOI-216 b to be a Super-puff

The planets of the TOI-216 system have been previously observed to exhibit large transit-timing variations, which enabled precise mass characterization of both transiting planets. In the first year of TESS observations, TOI-216 b exhibited grazing transits, precluding a measurement of its radius. In new observations, we demonstrate the orbit of the planet has precessed and it is now fully transiting, so we can accurately measure its radius. TOI-216 b is a puffy Neptune-mass planet, with a much larger radius that is now well constrained to R ⊕ and a density of 0.201 ± 0.017 g cm−3. We numerically integrate the system across the TESS observations to update and refine the masses and orbits of both planets, finding the uncertainty in the masses are now dominated by uncertainties in the stellar parameters. TOI-216 b represents a growing class of super-puff planets in orbital resonances and with a companion in a nearly circular orbit, suggesting the early evolution of these planets is driven by smooth disk migration.

TOI-2525 b and c: A Pair of Massive Warm Giant Planets with Strong Transit Timing Variations Revealed by TESS* ∗ Based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere under MPG program 0104.A-9007. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

The K-type star TOI-2525 has an estimated mass of M = M ⊙ and radius of R = R ⊙ observed by the TESS mission in 22 sectors (within sectors 1 and 39). The TESS light curves yield significant transit events of two companions, which show strong transit timing variations (TTVs) with a semiamplitude of ∼6 hr. We performed TTV dynamical and photodynamical light-curve analysis of the TESS data combined with radial velocity measurements from FEROS and PFS, and we confirmed the planetary nature of these companions. The TOI-2525 system consists of a transiting pair of planets comparable to Neptune and Jupiter with estimated dynamical masses of m b = and m c = M Jup, radii of r b = and r c = R Jup, and orbital periods of P b = and P c = days for the inner and outer planet, respectively. The period ratio is close to the 2:1 period commensurability, but the dynamical simulations of the system suggest that it is outside the mean-motion resonance (MMR) dynamical configuration. Object TOI-2525 b is among the lowest-density Neptune-mass planets known to date, with an estimated median density of ρ b = g cm−3. The TOI-2525 system is very similar to the other K dwarf systems discovered by TESS, TOI-2202 and TOI-216, which are composed of almost identical K dwarf primaries and two warm giant planets near the 2:1 MMR.

Magnesium oxide-water compounds at megabar pressure and implications on planetary interiors

Magnesium Oxide (MgO) and water (H2O) are abundant in the interior of planets. Their properties, and in particular their interaction, significantly affect the planet interior structure and thermal evolution. Here, using crystal structure predictions and ab initio molecular dynamics simulations, we find that MgO and H2O can react again at ultrahigh pressure, although Mg(OH)2 decomposes at low pressure. The reemergent MgO-H2O compounds are: Mg2O3H2 above 400 GPa, MgO3H4 above 600 GPa, and MgO4H6 in the pressure range of 270–600 GPa. Importantly, MgO4H6 contains 57.3 wt % of water, which is a much higher water content than any reported hydrous mineral. Our results suggest that a substantial amount of water can be stored in MgO rock in the deep interiors of Earth to Neptune mass planets. Based on molecular dynamics simulations we show that these three compounds exhibit superionic behavior at the pressure-temperature conditions as in the interiors of Uranus and Neptune. Moreover, the water-rich compound MgO4H6 could be stable inside the early Earth and therefore may serve as a possible early Earth water reservoir. Our findings, in the poorly explored megabar pressure regime, provide constraints for interior and evolution models of wet planets in our solar system and beyond.

Search for planets around stars with wide brown dwarfs

Aims. This work aims to better understand the role of wide brown dwarf companions in planetary systems.Methods. We obtained high-resolution spectra of six bright stars with co-moving wide substellar companions with the high-resolution SONG, CARMENES, and STELLA spectrographs. We used these spectra to derive radial velocities together with a complete set of physical stellar parameters. We then investigated radial velocity signals and discuss the fraction of planets in such systems. We also re-analysed the ages of our targets, which were used to derive the physical parameters of wide brown dwarf companions. Finally, a compilation of systems with known planets from the literature was considered along with our sample to search for possible peculiarities in their parameter distributions.Results. Based on the derived ages of six observed systems, we re-computed the masses of the wide companions, confirming their substellar nature. We confirm planets in the HD 3651 and HIP 70849 systems and find a new planetary candidate in the HD 46588 system. In our survey, which is mostly sensitive to Neptune-mass planets at short periods of a few days and Saturn-mass planets at longer periods of hundreds of days, we derived a fraction of planets orbiting stars with wide brown dwarf companions below 70%, with the uncertainties included. Comparing the parameter distributions of our sample with those of single stars, we observe the enhancement of planets with short periods below six days in systems with a wide stellar companion. Finally, planets in systems with wide brown dwarf companions follow their own eccentricity distribution with a maximum at ~0.65 and have periods longer than 40 days, masses higher than 0.1MJ, and eccentricities greater than 0.4.

The GAPS programme at TNG

Context. Neptunes represent one of the main types of exoplanets and have chemical-physical characteristics halfway between rocky and gas giant planets. Therefore, their characterization is important for understanding and constraining both the formation mechanisms and the evolution patterns of planets. Aims. We investigate the exoplanet candidate TOI-1422 b, which was discovered by the TESS space telescope around the high proper-motion G2 V star TOI-1422 (V = 10.6 mag), 155 pc away, with the primary goal of confirming its planetary nature and characterising its properties. Methods. We monitored TOI-1422 with the HARPS-N spectrograph for 1.5 yr to precisely quantify its radial velocity (RV) variation. We analyse these RV measurements jointly with TESS photometry and check for blended companions through high-spatial resolution images using the AstraLux instrument. Results. We estimate that the parent star has a radius of R⋆ = 1.019−0.013+0.014 R⊙, and a mass of M⋆ = 1.019−0.013+0.014 M⊙. Our analysis confirms the planetary nature of TOI-1422 b and also suggests the presence of a Neptune-mass planet on a more distant orbit, the candidate TOI-1422 c, which is not detected in TESS light curves. The inner planet, TOI-1422 b, orbits on a period of Pb = 12.9972 ± 0.0006 days and has an equilibrium temperature of Teq,b = 867 ± 17 K. With a radius of Rb = 3.96−0.11+0.13 R⊕, a mass of Mb = 9.0−2.0+2.3 M⊕ and, consequently, a density of ρb = 0.795−0.235+0.290g cm−3, it can be considered a warm Neptune-sized planet. Compared to other exoplanets of a similar mass range, TOI-1422 b is among the most inflated, and we expect this planet to have an extensive gaseous envelope that surrounds a core with a mass fraction around 10% – 25% of the total mass of the planet. The outer non-transiting planet candidate, TOI-1422 c, has an orbital period of Pc = 29.29−0.20+0.21 days, a minimum mass, Mcsin i, of 11.1−2.3+2.6 M⊕, an equilibrium temperature of Teq,c = 661 ± 13 K and, therefore, if confirmed, could be considered as another warm Neptune.

Solid Accretion onto Neptune-mass Planets. I. In Situ Accretion and Constraints from the Metallicity of Uranus and Neptune

The currently available, detailed properties (e.g., isotopic ratios) of solar system planets may provide guides for constructing better approaches to exoplanet characterization. With this motivation, we explore how the measured values of the deuterium-to-hydrogen (D/H) ratio of Uranus and Neptune can constrain their formation mechanisms. Under the assumption of in situ formation, we investigate three solid accretion modes: a dominant accretion mode switches from pebble accretion to drag-enhanced three-body accretion and to canonical planetesimal accretion, as the solid radius increases. We consider a wide radius range of solids that are accreted onto (proto)Neptune-mass planets and compute the resulting accretion rate as a function of both the solid size and the solid surface density. We find that for small-sized solids, the rate becomes high enough to halt concurrent gas accretion if all the solids have the same size. For large-sized solids, the solid surface density needs to be enhanced to accrete enough amounts of solids within the gas disk lifetime. We apply these accretion modes to the formation of Uranus and Neptune and show that if the minimum-mass solar nebula model is adopted, solids with a radius of ∼1 m to ∼10 km should have contributed mainly to their deuterium enrichment; a tighter constraint can be derived if the full solid size distribution is determined. This work therefore demonstrates that the D/H ratio can be used as a tracer of solid accretion onto Neptune-mass planets. Similar efforts can be made for other atomic elements that serve as metallicity indicators.

The GAPS Programme at TNG

Context. The measurement of the spin-orbit alignment of hot Jupiters, including a range of orbital and physical properties, can provide information about the evolution of the orbits of this special class of giant planets. Aims. We aim to refine the orbital and physical parameters and determine the sky-projected planet orbital obliquity λ of five eccentric (e ≅ 0.1–0.3) transiting planetary systems: HAT-P-15, HAT-P-17, HAT-P-21, HAT-P-26, and HAT-P-29, whose parent stars have an effective temperature between 5100 K &lt; Teff &lt; 6200 K. Each of the systems hosts a hot Jupiter, except for HAT-P-26, which hosts a Neptune-mass planet. Methods. We observed transit events of these planets with the HARPS-N spectrograph, obtaining high-precision radial velocity measurements that allow us to measure the Rossiter–McLaughlin effect for each of the target systems. We used these new HARPS-N spectra and archival data, including those from Gaia, to better characterise the stellar atmospheric parameters. The photometric parameters for four of the hot Jupiters were recalculated using 17 new transit light curves, obtained with an array of medium-class telescopes, and data from the TESS space telescope. HATNet time-series photometric data were checked for the signatures of rotation periods of the target stars and their spin axis inclination. Results. From the analysis of the Rossiter-McLaughlin effect, we derived a sky-projected obliquity of λ = 13° ± 6°, λ = −26.3° ± 6.7°, λ = −0.7° ± 12.5°, λ = −26° ± 16°, for HAT-P-15 b, HAT-P-17 b, HAT-P-21 b, and HAT-P-29 b, respectively. Based on theoretical considerations, these small values of λ should be of primordial origin, with the possible exception of HAT-P-21. Due to the quality of the data, we were not able to fully constrain λ for HAT-P-26 b, although a prograde orbit is favoured (λ = 18° ± 49°). The stellar activity of HAT-P-21 indicates a rotation period of 15.88 ± 0.02 days, which allowed us to determine its true misalignment angle ψ = 25° ± 16°. Our new analysis of the physical parameters of the five exoplanetary systems returned values compatible with those existing in the literature. Using TESS and the available transit light curves, we reviewed the orbital ephemeris for the five systems and confirmed that the HAT-P-26 system shows transit timing variations, which may tentatively be attributed to the presence of a third body.

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.