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Searches for helium in the exospheres of exoplanets via the metastable near-infrared triplet have yielded 17 detections and 40 nondetections. We performed a comprehensive reanalysis of published studies to investigate the influence of stellar X-ray and extreme-ultraviolet (XUV) flux and orbital parameters on the detectability of helium in exoplanetary atmospheres. We identified a distinct “orbital sweet spot” for helium detection, 0.03 to 0.08 au from the host star, where the majority of detections occurred. This sweet spot is influenced by the stellar luminosity and planet size. Notably, a lower ratio of XUV flux to mid-UV flux is preferred for planets compared to nondetections. We also found that helium detections occur for planets around stars with effective temperatures of 4400–6500 K (i.e., spectral type K and G stars), with a sharp gap between 5400 and 6000 K, where no detections occur. We also report an upper-limit efficiency of 6% for energy-limited atmospheric escape from our analysis. Additionally, our analysis of the cumulative XUV flux versus escape velocity shows planets with helium detections above the “cosmic shoreline,” where atmospheres are not thought to be present, suggesting the shoreline needs revision. The unexpected trends revealed in our meta-analysis can contribute to a better understanding of star–planet interaction and exosphere evolution.

Ultra-hot Jupiters exhibit day-to-night temperature contrasts upwards of 1000 K due to competing effects of strong winds, short radiative timescales, magnetic drag, and H2 dissociation/recombination. Spectroscopic phase curves provide critical insights into these processes by mapping temperature distributions and constraining the planet’s energy budget across different pressure levels. Here, we present the first NIRISS/SOSS phase curve of an ultra-hot Jupiter, WASP-121 b. The instrument’s bandpass [0.6–2.85 μm] captures an estimated 50%–83% of the planet’s bolometric flux, depending on orbital phase, allowing for unprecedented constraints on the planet’s global energy budget; previous measurements with HST/WFC3 and JWST/NIRSpec/G395H captured roughly 20% of the planetary flux. Accounting for the unobserved regions of the spectrum, we estimate effective day- and nightside temperatures of Tday = 2717 ± 17 K and Tnight=1562−19+18 K corresponding to a Bond albedo of AB = 0.277 ± 0.016 and a heat recirculation efficiency of ϵ = 0.246 ± 0.014. Matching the phase-dependent effective temperature with energy balance models yields a similar Bond albedo of 0.3 and a mixed layer pressure of 1 bar consistent with photospheric pressures, but unexpectedly slow winds of 0.2 km s−1, indicative of inefficient heat redistribution. The shorter optical wavelengths of the NIRISS/SOSS Order 2 yield a geometric albedo of Ag=0.093−0.027+0.029 (3σ upper limit of 0.175), reinforcing the unexplained trend of hot Jupiters exhibiting larger Bond than geometric albedos. We also detect near-zero phase curve offsets for wavelengths above 1.5 μm, consistent with inefficient heat transport, while shorter wavelengths potentially sensitive to reflected light show eastward offsets.

Atmospheric escape of close-in exoplanets, driven by stellar irradiation, influences their evolution, composition, and atmospheric dynamics. The near-infrared metastable helium triplet (10833 Å) has become a key probe of this process, enabling mass loss rate measurements for dozens of exoplanets. Only a few studies, however, have detected absorption beyond transit, supporting the presence of hydrodynamic outflows. None have yet precisely identified the physical extent of the out-of-transit signal, either due to non-continuous or short-duration observations. This strongly limits our ability to measure accurate mass-loss rates and to understand how the stellar environment shapes outflows. Here we present the continuous, full-orbit helium phase-curve observation of an exoplanet: the ultra-hot Jupiter WASP-121 b, obtained with the James Webb Space Telescope (JWST) and the Near Infrared Imager and Slitless Spectrograph (NIRISS). We detect significant helium absorption at  > 3 σ over nearly 60% of the orbit, revealing a persistent and large-scale outflow. The signal separates into a dense leading tail moving toward the star and a trailing tail pushed away by stellar irradiation. Both appear to remain collisional far from the planet, implying strong hydrodynamic escape. While qualitatively consistent with theoretical expectations, current models cannot reproduce the full spatial and kinematic structure, limiting precise mass-loss estimates. These results demonstrate JWST’s ability to map exoplanet outflows in detail and highlight its synergy with ground-based spectroscopy. JWST observations of the ultra hot Jupiter WASP 121 b reveal helium escaping for most of its orbit, forming two giant tails moving in opposite directions. The results show how stellar radiation modifies planetary atmospheres.

Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (P orb) of 12.76 days. The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous P orb from TESS data. We confirmed the transit signal and P orb using ground-based photometry with MuSCAT2 and MuSCAT3, and validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host star is inactive, with an X-ray-to-bolometric luminosity ratio of logLX/Lbol≈−5.7 . Joint analysis of the light curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R ⊕, a 3σ mass upper limit of 3.9 M ⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric (TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.

We present the discovery and validation of a temperate sub-Neptune around the nearby mid-M dwarf TIC 470381900 (TOI-1696), with a radius of 3.09 ± 0.11 R ⊕ and an orbital period of 2.5 days, using a combination of Transiting Exoplanets Survey Satellite (TESS) and follow-up observations using ground-based telescopes. Joint analysis of multiband photometry from TESS, Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets (MuSCAT), MuSCAT3, Sinistro, and KeplerCam confirmed the transit signal to be achromatic as well as refined the orbital ephemeris. High-resolution imaging with Gemini/’Alopeke and high-resolution spectroscopy with the Subaru InfraRed Doppler (IRD) confirmed that there are no stellar companions or background sources to the star. The spectroscopic observations with IRD and Infrared Telescope Facility SpeX were used to determine the stellar parameters, and it was found that the host star is an M4 dwarf with an effective temperature of T eff = 3185 ± 76 K and a metallicity of [Fe/H] = 0.336 ± 0.060 dex. The radial velocities measured from IRD set a 2σ upper limit on the planetary mass to be 48.8 M ⊕. The large radius ratio (R p/R ⋆ ∼ 0.1) and the relatively bright near-infrared magnitude (J = 12.2 mag) make this planet an attractive target for further follow-up observations. TOI-1696 b is one of the planets belonging to the Neptunian desert with the highest transmission spectroscopy metric discovered to date, making it an interesting candidate for atmospheric characterizations with JWST.

We report on the discovery of an Earth-sized transiting planet (R p = 1.015 ± 0.051 R ⊕) in a P = 4.02 day orbit around K2-415 (EPIC 211414619), an M5V star at 22 pc. The planet candidate was first identified by analyzing the light-curve data obtained by the K2 mission, and it is here shown to exist in the most recent data from TESS. Combining the light curves with the data secured by our follow-up observations, including high-resolution imaging and near-infrared spectroscopy with IRD, we rule out false-positive scenarios, finding a low false-positive probability of 2 × 10−4. Based on IRD’s radial velocities of K2-415, which were sparsely taken over three years, we obtain a planet mass of 3.0 ± 2.7 M ⊕ (M p < 7.5 M ⊕ at 95% confidence) for K2-415b. Being one of the lowest-mass stars (≈0.16 M ⊙) known to host an Earth-sized transiting planet, K2-415 will be an interesting target for further follow-up observations, including additional radial velocity monitoring and transit spectroscopy.

Searches for helium in the exospheres of exoplanets via the metastable near-infrared triplet have yielded 17 detections and 40 non-detections. We performed a comprehensive re-analysis of published studies to investigate the influence of stellar XUV flux and orbital parameters on the detectability of helium in exoplanetary atmospheres. We identified a distinct 'orbital sweet spot' for helium detection, 0.03 to 0.08 AU from the host star, where the majority of detections occurred. This sweet spot is influenced by the stellar XUV flux and planet size. Notably, a lower ratio of XUV flux to mid-UV flux is preferred for planets compared to non-detections. We also found that helium detections occur for planets around stars with effective temperatures of 4400-6500 K, with a sharp gap at 5400 to 6000 K, where no detections occur. Additionally, our analysis of the cumulative XUV flux versus escape velocity shows planets with helium detections are found above the 'cosmic shoreline', suggesting the shoreline needs revision. The trends we found in our analysis contribute to a deeper understanding of exosphere evolution.

High-resolution thermal emission spectroscopy provides a powerful probe of atmospheric circulation in ultra-hot Jupiters (UHJs), with Doppler shifts encoding information about the 3D wind field across the planet disk. Retrieving these wind properties from phase-dependent emission spectra requires a forward model that is both physically motivated and computationally tractable. We present dopplerkernel, a new forward model that parametrizes the projected line-of-sight velocity field on the planet disk using four wind parameters (an equatorial jet speed \\(v_jet\\) and width \\(_jet\\), a source-to-sink flow speed \\(v_wind\\), and a flow convergence longitude \\(_sink\\)) and constructs a broadening kernel via weighted kernel-density estimation. We apply this framework in a Bayesian retrieval to synthetic \\(K\\)-band emission spectra of WASP-76b generated from three 3D GCM outputs. Our retrievals successfully recover the equatorial jet in the drag-free GCM to within \\(1\\) km/s of the zonal mean and infer day-to-night wind speeds in good agreement with GCM averages at 1-10 mbar for all three drag regimes. We find that spectral resolutions of \\(R 100,000\\) offer an optimal trade-off: sufficient to resolve global wind features while avoiding spurious detections caused by model-data mismatches at higher resolution. Combining pre- and post-eclipse phases yields more reliable constraints than either alone, particularly on the orientation of the source-to-sink flow. Experiments with more complex weight functions reveal a degeneracy between the velocity field and the thermal weighting, cautioning against overparametrization. In conclusion, a parametric broadening-kernel model with a small number of physically interpretable parameters can accurately reproduce the phase-dependent line shifts, shapes, and strengths in UHJ emission spectra.

Ultra-hot Jupiters showcase extreme atmospheric conditions, including molecular dissociation, ionisation, and significant day-to-night temperature contrasts. Their close proximity to host stars subjects them to intense stellar irradiation, driving high temperatures where hydride ions (H\\(^-\\)) significantly contribute to opacity, potentially obscuring metal features in near-infrared transmission spectra. We investigate the atmosphere of WASP-189b, targeting atomic, ionic, and molecular species (H, He, Fe, Ti, V, Mn, Na, Mg, Ca, Cr, Ni, Y, Ba, Sc, Fe\\(^+\\), Ti\\(^+\\), TiO, H\\(_2\\)O, CO, and OH), focusing on (i) the role of H\\(^-\\) as a source of continuum opacity, and (ii) the relative hydride-to-Fe abundance using joint optical and near-infrared data. We present two transits of WASP-189b gathered simultaneously in the optical with HARPS and near-infrared with NIRPS, supported by photometric light curves from EulerCam and ExTrA. Transmission spectra were analysed via cross-correlation to detect absorption features and enhance the signal-to-noise ratio. Atmospheric retrievals quantified relative abundances by fitting overall metallicity and proxies for TiO, H\\(^-\\), and e\\(^-\\). Only atomic iron is detected in HARPS data (S/N ~5.5), but not in NIRPS, likely due to H\\(^-\\) continuum dampening. Retrievals on HARPS-only and HARPS+NIRPS suggest the hydride-to-Fe ratio exceeds equilibrium predictions by about 0.5 dex, hinting at strong hydrogen ionisation. Including NIRPS data helps constrain H\\(^-\\) abundance and set an upper limit on free electron density, unconstrained in HARPS-only data. These results emphasise H\\(^-\\) as a significant continuum opacity source impeding detection of planetary absorption features in WASP-189b's near-infrared transmission spectrum.