Courtney D. Dressing

We characterize the radius-dependent observed transiting eccentricity distribution of 219 warm ( P = 8–50 days) systems with only one transiting planetary candidate identified during Sectors 1–69 of the Transiting Exoplanet Survey Satellite (TESS) mission. Using the “photoeccentric effect” in a hierarchical Bayesian framework, we first model the population using discrete planetary size bins (sub-Neptunes, sub-Saturns, and Jovians). We then develop a continuous mixture model with weights governed by a logistic sigmoid function of radius. We find that the warm-single population is best described by two components: a dominant low-eccentricity mode (〈 e _low 〉 = 0.03 9 − 0.038 + 0.018 ) and a secondary dynamically excited mode (〈 e _high 〉 = 0.46 6 − 0.068 + 0.067 ). The fraction of planets belonging to this high-eccentricity component increases strongly with planet radius, characterized by a transition at a break radius of R _br = 9 . 2 − 1.1 + 1.9 R _⊕ . This trend places warm sub-Saturns predominantly on the same low-eccentricity track as sub-Neptunes. In contrast, warm Jovians (8–16 R _⊕ ) are frequently eccentric, with 6 5 − 12 + 13 % of the population in the high-eccentricity mode. Under the assumption of a two-component model, we see tentative evidence for a bimodal Jovian distribution at ∼2.7 σ . Finally, we identify a nonnegligible tail of highly eccentric sub-Neptunes (1–4 R _⊕ ), which comprise 16 . 2 − 6.4 + 5.2 % of the population, consistent with excitation by nontransiting external companions.

M dwarfs are the most common sites of planet formation in the Milky Way. Planet occurrence and composition are closely linked with the availability of metals in protoplanetary disks, which can be probed by measuring the metallicity of planet host stars. In this work, we measure the metallicities ([M/H] and [Fe/H]) of 59 M dwarfs hosting 76 planets and candidates using medium-resolution near-infrared spectra collected with IRTF/SpeX. We combine these results with literature metallicity measurements for planet-hosting cool dwarfs, and present a sample of 86 stars hosting 142 candidate, validated, and confirmed planets with homogeneously derived stellar parameters. Using our updated stellar radii, we calculate planet radii from TESS transit depths for both the confirmed ( N = 51, 0.6–12.5 R _⊕ , median R _p = 1.8 R _⊕ ) and candidate ( N = 25, 0.6–7.2 R _⊕ , median R _p = 2.1 R _⊕ ) planets. We compare the metallicity distributions of super-Earth and sub-Neptune host stars, finding that M dwarfs hosting sub-Neptunes are statistically more metal-rich than those hosting super-Earths. This result is robust to the radius valley prescription used and is likely not due to differences in the stellar samples considered. This result supports the hypothesized formation pathway whereby sub-Neptunes form beyond the water ice line where they can accrete volatiles before migrating inward to their observed locations. The enhanced inventories of refractory elements throughout the disk and of volatiles beyond the ice line in metal-rich disks around low-mass stars may contribute to the preference seen in the observed planet sample for sub-Neptunes to orbit metal-rich M dwarfs.

The present-day architecture of planetary systems contains information about their formation and migration histories. The origin of hot Jupiters (HJs; P łesssim 10 d, R_ ̊m p > 8 R_⊕) has long been a matter of debate. While most of them are found to be `lonely', there is a rare population of HJs hosting small inner-orbit companions (eight known as of May 2026). Their peculiar architecture suggests a gentle disc-migration mechanism. In this study, we present the discovery and characterisation of the multi-planet system TOI-1533, comprising an inner sub-Neptune (TOI-1533 b, P_ ̊m orb = 3.63 d, R_ ̊m p = 3.15 R_⊕) and an outer hot giant planet (TOI-1533 c, P_ ̊m orb = 8.06 d, R_ ̊m p > 7.5 R_⊕) with substantial H/He by mass (ρ_ ̊m p < 0.48 g cm -3 $), both transiting an active K-dwarf star (T_ ̊m eff ≈ 5130 K; V (mag) ≈ 11). Our joint modelling of stellar activity and planetary signals from radial velocities (HARPS-N) and transits (TESS) allowed us to detect the planetary Keplerian signals (approximately 10 σ) and isolate the stellar modulation. The inclusion of simultaneous photometry in the multi-dimensional Gaussian processes formalism was a fundamental addition to the spectroscopic activity indicators, enabling the disentanglement of stellar activity from planetary signals. The mass ratio of the two confirmed planets (M_ ̊m b / M_ ̊m c about 0.8), together with the super-Neptune mass of the large outer companion ($M_ ̊m c ≈ 40 M_⊕), makes this system unusual compared to the other known HJs with low-mass inner companions.

The radii of small exoplanets form two populations, super-Earths and sub-Neptunes, separated by a gap known as the radius valley. This feature could be produced by the removal of atmospheres by stellar or internal heating or by the lack of an initial envelope. We used transit photometry and radial velocity measurements to detect and characterize four exoplanets orbiting LHS 1903, a red dwarf star in the Milky Way’s thick disk. These four planets have orbital periods ranging from 2.2 to 29.3 days and span the radius valley within a single planetary system. The derived densities indicate that LHS 1903 b is rocky, whereas LHS 1903 c and LHS 1903 d have extended atmospheres. The most distant planet from the host star, LHS 1903 e, has no gaseous envelope, indicating that it formed from gas-depleted material.

Unresolved stellar companions can cause both underestimations in the radii of transiting planets and overestimations of their detectability, affecting our ability to reliably measure planet occurrence rates. To quantify the latter, we identified a control sample of 198 Kepler stars with sensitivity to Earth-like planets if they were single stars, and imaged them with adaptive optics. In 20% of systems, we detected stellar companions that were close enough to go unresolved in Kepler observations. We calculated the distribution of planet radius correction factors needed to adjust for these observed companions, along with simulations of undetected companions to which our observations were not sensitive. We then used these correction factors to optimize an occurrence rate model for small, close-in planets while correcting Kepler’s detection efficiency for the presence of unresolved companions, and quantified how this correction affects occurrence estimates. Median occurrence rates for small planets between 2 and 100 days increased by an average factor of 1.08–1.19 (depending on statistical treatments), with the largest differences found for smaller planets at larger orbital periods. We found that the frequency of Earth-sized planets in the habitable zone ( η _⊕ ) increased by a factor of 1.18 − 0.66 + 0.43 – 1.46 − 0.83 + 0.53 when accounting for the effect of unresolved companions on Kepler’s detection sensitivity.

A goal of the future Habitable Worlds Observatory (HWO) is to directly image and spectroscopically characterize true Earth-analogs. However, if a large fraction of HWO target stars host unknown dynamically disruptive giant planets in their habitable zones (HZs), then additional targets that are farther away will need to be surveyed, potentially requiring a larger-aperture telescope and a coronagraph with a smaller inner working angle. Therefore, the sooner we constrain the presence of massive planets orbiting potential HWO target stars, the easier and less costly it will be to adjust key aspects of HWO’s architecture. In this work, we uniformly analyze over 153,000 public radial velocity (RV) observations of 120 potential HWO target stars to derive mass limits on planetary companions. The RVs were measured by 23 spectrographs located at 15 observatories around the world, with the first observations going back to 1987. Based on empirical search completeness tests, we determine that undetected Jupiter-mass (Saturn-mass) planets may be hiding in up to 38% (53%) of the HZs of targets in the ExEP Mission Star List. The median mass sensitivity limit in the middle of the conservative HZ is approximately 48 M _⊕ . We also provide updated parameters for 53 known companions, and we detect at least 26 additional RV signals corresponding to stellar activity and 4 signals that are planet candidates. We note that 44 of the ExEP stars lack substantial RV monitoring history, and we advocate for community-coordinated observing campaigns of these stars using moderate-precision RV facilities.

We present the discovery of 30 transiting giant planets that were initially detected using data from NASA’s Transiting Exoplanet Survey Satellite mission. These new planets orbit relatively bright (G ≤ 12.5) FGK host stars with orbital periods between 1.6 and 8.2 days, and have radii between 0.9 and 1.7 Jupiter radii. We performed follow-up ground-based photometry, high angular resolution imaging, high-resolution spectroscopy, and radial velocity monitoring for each of these objects to confirm that they are planets and determine their masses and other system parameters. The planets’ masses span more than an order of magnitude (0.17 M _J < M _p < 3.3 M _J). For two planets, TOI-3593 b and TOI-4961 b, we measured significant nonzero eccentricities of 0.1 1 − 0.03 + 0.05 and 0.1 8 − 0.05 + 0.04 , respectively, while for the other planets, the data typically provide a 1σ upper bound of 0.15 on the eccentricity. These discoveries represent a major step toward assembling a complete, magnitude-limited sample of transiting hot Jupiters around FGK stars.

We confirm the planetary nature of a pair of transiting sub-Neptune exoplanets orbiting the bright F-type subgiant star TOI-6054 (V = 8.02, K = 6.673) as a part of the OrCAS radial velocity survey using WIYN/NEID observations. We find that TOI-6054b and TOI-6054c have radii of 2.64 ± 0.15R _⊕ and 2.82 ± 0.17R _⊕, respectively, and masses of 12.5 ± 1.7M _⊕ and 9.3 ± 1.9M _⊕. The planets have zero-albedo equilibrium temperatures of 1360 ± 32 K and 1143 ± 28 K. The host star has expanded and will evolve off of the main sequence within the next ∼500 Myr, and the resulting increase in stellar luminosity has more than doubled the stellar flux the two planets receive compared to the start of the host star’s main-sequence phase. Consequently, TOI-6054b may be losing some of its primordial hydrogen/helium atmosphere—if it has one. Based on dynamical simulations performed using the orbital parameters of the two planets, TOI-6054b, and TOI-6054c are very likely in a 5:3 mean motion resonance. The TOI-6054 system thus has the potential to be an excellent candidate for future atmospheric follow-up observations, with two similarly sized sub-Neptunes around a bright star. We also estimate that if TOI-6054b is currently losing its H/He atmosphere, this should be observable from space and from the ground.

We characterize the atmosphere of the hot super-Neptune WASP-166b (P = 5.44 days, R _p = 6.9 ± 0.3 R _⊕, M _p = 32.1 ± 1.6 M _⊕, T _eq = 1270 ± 30 K) orbiting an F9V star using JWST transmission spectroscopy with NIRISS and NIRSpec (0.85–5.17 μm). With this broad wavelength range, NIRISS provides strong constraints on H₂O and clouds (where NIRSpec performs poorly) while NIRSpec captures CO₂ and NH₃ (where NIRISS performs poorly). Our POSEIDON free chemistry retrievals confirm the detection of H₂O (15.2σ significance) and detect CO₂ (14.7σ) for the first time. We also find a possible hint of NH₃ (2.3σ) and an intermediate pressure cloud deck (2.6σ). Finally, we report inconclusive support for the presence of SO₂, CO, and Na, as well as nondetections of CH₄, C₂H₂, HCN, H₂S, and K. We verify our results using a TauREx free chemistry retrieval. We also measure with POSEIDON equilibrium chemistry retrievals a superstellar planetary atmospheric metallicity ( log ( Z ) = 1.5 7 − 0.18 + 0.17 , Z = 3 7 − 13 + 18 ) and planetary C/O ratio ( C / O = 0.28 2 − 0.053 + 0.078 ) consistent with the stellar C/O ratio (C/O_* = 0.41 ± 0.08). These results are compatible with various planetary formation pathways, especially those that include planetesimal accretion followed by core erosion or photoevaporation. WASP-166b also resides near the edge of the Hot Neptune Desert, a sparse population of intermediate-sized planets at high insolation fluxes; thus, these results and further atmospheric observations of Hot Neptunes will help determine the driving processes in the formation of the Hot Neptune Desert.