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Abstract The “Neptunian ridge” is a recently identified peak in the frequency of planets with sizes between that of Neptune and Saturn orbiting their host stars with periods between 3 and 6 days. These planets may have formed similarly to their larger, hot Jupiter counterparts in the “3 day pileup,” through a dynamically excited migration pathway. The distribution of stellar obliquities in hot Neptune systems may therefore provide a vital clue as to their origin. We report a new stellar obliquity measurement for TOI-2374b, a planet in the Neptunian ridge (P= 4.31 days,R_p = 7.5R_⊕). We observed a spectroscopic transit of TOI-2374b with the Keck Planet Finder, detecting the Rossiter–McLaughlin (RM) anomaly with an amplitude of 3 m s⁻¹, and measured a sky-projected obliquity of $\lambda ={81°}_{-22^{\circ }}^{+23^{\circ }}$ , indicating an orbit significantly misaligned with the spin axis of its host star. A reloaded RM analysis of the cross-correlation functions confirms this misalignment, measuring $\lambda ={65°}_{-24^{\circ }}^{+32^{\circ }}$ . Additionally, we measured a stellar rotation period of $P_{\mathrm{rot}}=26.4_{-0.8}^{+0.9}$ days with photometry from theTierrasobservatory, allowing us to deduce the three-dimensional stellar obliquity of $\psi ={85\stackrel{°}{.}9}_{-9\stackrel{°}{.}2}^{+8\stackrel{°}{.}6}$ . TOI-2374b joins a growing number of hot Neptunes on polar orbits. The high frequency of misaligned orbits for Neptunian ridge and desert planets, compared with their longer period counterparts, is reminiscent of patterns seen for the giant planets and may suggest a similar formation mechanism. 

Abstract We present a ground-based transit detection of HIP 41378 f, a long-period (P= 542 days), extremely low-density (0.09 ± 0.02 g cm⁻³) giant exoplanet in a dynamically complex system. Using photometry fromTierras, TRAPPIST-North, and multiple Las Cumbres Observatory Global Telescope sites, we constrain the transit center time toT_C,6 = 2460438.891 ± 0.052 BJD TDB. This marks only the second ground-based detection of HIP 41378 f, currently the longest-period and longest-duration transiting exoplanet observed from the ground. We use this new detection, along with a recently published transit time from Rossiter–McLaughlin observations, to update the transit timing variation (TTV) solution for HIP 41378 f. We predict the next two transits will occur at $T_{C,7}=2460980.793_{-0.129}^{+0.098}$ BJD TDB (2025 November 1) and $T_{C,8}=2461522.653_{-0.238}^{+0.213}$ BJD TDB (2027 April 27). Incorporating new TESS Sector 88 data, we also rule out the 101 days orbital period alias for HIP 41378 d, and find that the remaining viable solutions are centered on the 278, 371, and 1113 days aliases. The latter two imply dynamical configurations that challenge the canonical view of planet e as the dominant perturber of planet f. Our results suggest that HIP 41378 d may instead play the leading role in shaping the TTV of HIP 41378 f. 

Abstract We present the discovery and characterization of TOI-4364b, a young mini-Neptune in the tidal tails of the Hyades cluster, identified through TESS transit observations and ground-based follow-up photometry. The planet orbits a bright M dwarf (K= 9.1 mag) at a distance of 44 pc, with an orbital period of 5.42 days and an equilibrium temperature of $488_{-7}^{+9}$ K. The host star's well-constrained age of 710 Myr makes TOI-4364b an exceptional target for studying early planetary evolution around low-mass stars. We determined a planetary radius of $2.01_{-0.08}^{+0.10}{R}_{\oplus }$ , indicating that this planet is situated near the upper edge of the radius valley. This suggests that the planet retains a modest H/He envelope. As a result, TOI-4364b provides a unique opportunity to explore the transition between rocky super-Earths and gas-rich mini-Neptunes at the early stages of evolution. Its radius, which may still evolve as a result of ongoing atmospheric cooling, contraction, and photoevaporation, further enhances its significance for understanding planetary development. Furthermore, TOI-4364b’s moderately high transmission spectroscopy metric of 44.2 positions it as a viable candidate for atmospheric characterization with instruments such as JWST. This target has the potential to offer crucial insights into atmospheric retention and loss in young planetary systems. 

Abstract Young planets with mass measurements are particularly valuable in studying atmospheric mass-loss processes, but these planets are rare and their masses difficult to measure due to stellar activity. We report the discovery of a planetary system around TOI-6109, a young, 75 Myr-old Sun-like star in the Alpha Persei cluster. It hosts at least two transiting Neptune-like planets within 10 day orbital periods. Using three TESS sectors, 30 CHEOPS orbits, and photometric follow-up observations from the ground, we confirm the signals of the two planets. TOI-6109 b has an orbital period ofP= $5.6904_{-0.0004}^{+0.0004}$ days and a radius ofR= $4.87_{-0.12}^{+0.16}$ R_⊕. The outer planet, TOI-6109 c has an orbital period ofP= $8.5388_{-0.0005}^{+0.0006}$ days and a radius ofR= $4.83_{-0.06}^{+0.07}$ R_⊕. These planets orbit just outside a 3:2 mean motion resonance. The near-resonant configuration presents the opportunity to measure the planet’s mass via TTV measurements and to bypass difficult RV measurements. Measuring the masses of the planets in this system will allow us to test theoretical models of atmospheric mass loss. 

ABSTRACT Transit timing variations (TTVs) can be induced by a range of physical phenomena, including planet–planet interactions, planet–moon interactions, and stellar activity. Recent work has shown that roughly half of moons would induce fast TTVs with a short period in the range of 2–4 orbits of its host planet around the star. An investigation of the Kepler TTV data in this period range identified one primary target of interest, Kepler-1513 b. Kepler-1513 b is a $$8.05^{+0.58}_{-0.40}$$ R⊕ planet orbiting a late G-type dwarf at $$0.53^{+0.04}_{-0.03}$$ au. Using Kepler photometry, this initial analysis showed that Kepler-1513 b’s TTVs were consistent with a moon. Here, we report photometric observations of two additional transits nearly a decade after the last Kepler transit using both ground-based observations and space-based photometry with TESS. These new transit observations introduce a previously undetected long period TTV, in addition to the original short period TTV signal. Using the complete transit data set, we investigate whether a non-transiting planet, a moon, or stellar activity could induce the observed TTVs. We find that only a non-transiting perturbing planet can reproduce the observed TTVs. We additionally perform transit origami on the Kepler photometry, which independently applies pressure against a moon hypothesis. Specifically, we find that Kepler-1513 b’s TTVs are consistent with an exterior non-transiting ∼Saturn mass planet, Kepler-1513 c, on a wide orbit, $$\sim 5~{{\ \rm per \, cent}}$$ outside a 5:1 period ratio with Kepler-1513 b. This example introduces a previously unidentified cause for planetary interlopers in the exomoon corridor, namely an insufficient baseline of observations. 

Abstract We present the discovery of 11 new transiting brown dwarfs (BDs) and low-mass M dwarfs from NASA’s Transiting Exoplanet Survey Satellite (TESS) mission: TOI-2844, TOI-3122, TOI-3577, TOI-3755, TOI-4462, TOI-4635, TOI-4737, TOI-4759, TOI-5240, TOI-5467, and TOI-5882. They consist of five BD companions and six very-low-mass stellar companions ranging in mass from 25M_Jto 128M_J. We used a combination of photometric time-series, spectroscopic, and high-resolution imaging follow-up as a part of the TESS Follow-up Observing Program (or TFOP) to characterize each system. With over 50 transiting BDs confirmed, we now have a large enough sample to directly test different formation and evolutionary scenarios. We provide a renewed perspective on the transiting “brown dwarf desert” and its role in differentiating between planetary and stellar formation mechanisms. Our analysis of the eccentricity distribution for the transiting BD sample does not support previous claims of a transition between planetary and stellar formation at ∼42M_J. We also contribute a first look into the metallicity distribution of transiting companions in the range 7–150M_J, showing that this does not support a ∼42M_Jtransition too. Finally, we also detect a significant lithium absorption feature in one of the BD hosts (TOI-5882). However, we determine that the host star is likely old based on rotation, kinematic, and photometric mdeasurements. We therefore claim that TOI-5882 may be a candidate for planetary engulfment. 

ABSTRACT Growing numbers of exoplanet detections continue to reveal the diverse nature of planetary systems. Planet formation around late-type M dwarfs is of particular interest. These systems provide practical laboratories to measure exoplanet occurrence rates for M dwarfs, thus testing how the outcomes of planet formation scale with host mass, and how they compare to Sun-like stars. Here, we report the discovery of TOI-6478 b, a cold ($$T_{\text{eq}}=204\,$$ K) Neptune-like planet orbiting an M5 star ($$R_\star =0.234\pm 0.012\, \text{R}_\odot$$, $$M_\star =0.230\pm 0.007\, \text{M}_\odot$$, $$T_{\text{eff}}=3230\pm 75\,$$ K) that is a member of the Milky Way’s thick disc. We measure a planet radius of $$R_b=4.6\pm 0.24\, \text{R}_{\oplus }$$ on a $$P_b=34.005019\pm 0.000025\,$$ d orbit. Using radial velocities, we calculate an upper mass limit of $$M_b\le 9.9\, \text{M}_{\oplus }$$ ($$M_b\le 0.6\, \text{M}_{\text{Nep}})$$, with $$3\, \sigma$$ confidence. TOI-6478 b is a milestone planet in the study of cold Neptune-like worlds. Due to its large atmospheric scale height, it is amenable to atmospheric characterization with facilities such as JWST, and will provide an excellent probe of atmospheric chemistry in this cold regime. It is one of very few transiting exoplanets that orbit beyond their system’s ice-line whose atmospheric chemical composition can be measured. Based on our current understanding of this planet, we estimate TOI-6478 b’s spectroscopic features (in transmission) can be $$\sim 2.5\times$$ as high as the widely studied planet K2-18 b. 

Astronomers have found more than a dozen planets transiting stars that are 10–40 million years old1, but younger transiting planets have remained elusive. The lack of such discoveries may be because planets have not fully formed at this age or because our view is blocked by the protoplanetary disk. However, we now know that many outer disks are warped or broken2; provided the inner disk is depleted, transiting planets may thus be visible. Here we report observations of the transiting planet IRAS 04125+2902 b orbiting a 3-million-year-old, 0.7-solar-mass, pre-main-sequence star in the Taurus Molecular Cloud. The host star harbours a nearly face-on (30 degrees inclination) transitional disk3 and a wide binary companion. The planet has a period of 8.83 days, a radius of 10.7 Earth radii (0.96 Jupiter radii) and a 95%-confidence upper limit on its mass of 90 Earth masses (0.3 Jupiter masses) from radial-velocity measurements, making it a possible precursor of the super-Earths and sub-Neptunes frequently found around main-sequence stars. The rotational broadening of the star and the orbit of the wide (4 arcseconds, 635 astronomical units) companion are both consistent with edge-on orientations. Thus, all components of the system are consistent with alignment except the outer disk; the origin of this misalignment is unclear. 

Abstract We report the validation of multiple planets transiting the nearby (d= 12.8 pc) K5V dwarf HD 101581 (GJ 435, TOI–6276, TIC 397362481). This system consists of at least two Earth-size planets whose orbits are near a mutual 4:3 mean-motion resonance, HD 101581 b ( $R_p={0.956}_{-0.061}^{+0.063}{R}_{\oplus }$ ,P= 4.47 days) and HD 101581c ( $R_p={0.990}_{-0.070}^{+0.070}{R}_{\oplus }$ ,P= 6.21 days). Both planets were discovered in Sectors 63 and 64 TESS observations and statistically validated with supporting ground-based follow-up. We also identify a signal that probably originates from a third transiting planet, TOI-6276.03 ( $R_p={0.982}_{-0.098}^{+0.114}{R}_{\oplus }$ ,P= 7.87 days). These planets are remarkably uniform in size and their orbits are evenly spaced, representing a prime example of the “peas-in-a-pod” architecture seen in other compact multiplanet systems. AtV= 7.77, HD 101581 is the brightest star known to host multiple transiting planets smaller than 1.5R_⊕. HD 101581 is a promising system for atmospheric characterization and comparative planetology of small planets.