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With dayside temperatures hot enough to sustain a magma ocean and a silicate atmosphere, lava planets are the best targets to study the atmosphere of a rocky world. In the absence of nightside heating, the entire atmosphere collapses near the day-night terminator, so condensation seems inevitable, but the impact of clouds on radiative transfer, dynamics, and observables has not yet been studied in the non-global atmospheric regime. Therefore, we simulate cloud formation and determine which lava planets should be most affected by clouds. We find that despite the scattering of visible light by clouds, heat advection compensates for the cooling effect of clouds in the atmosphere. On the other hand, surface temperatures are significantly affected and can drop 100-200 K under a cloudy sky. We find that among our targets, HD213885b and HD20329b are most affected by cloud formation: there is a discernable difference between having clouds and not having them, but the precision required to make such an inference is at the limit of current instruments., Comment: 15 pages, 7 figures; revised manuscript under review

High-eccentricity gas giant planets serve as unique laboratories for studying the thermal and chemical properties of H/He-dominated atmospheres. One of the most extreme cases is HD 80606b -- a hot Jupiter orbiting a sun-like star with an eccentricity of $0.93$ -- which experiences an increase in incident flux of nearly three orders of magnitude as the star-planet separation decreases from $0.88\,{\rm au}$ at apoastron to $0.03\,{\rm au}$ at periastron. We observed the planet's periastron passage using \emph{JWST}'s NIRSpec/G395H instrument ($2.8-5.2\,{\rm \mu m}$) during a $21\,{\rm hr}$ window centered on the eclipse. We find that, as the planet passes through periastron, its emission spectrum transitions from a featureless blackbody to one in which CO and CH$_4$ absorption features are visible. We obtain significant detections of CH$_4$ during post-periapse phases at $3.7-4.8\sigma$ depending on the phase. Following periapse, CO and H$_2$O are also detected at $3.4\sigma$ and $3.1\sigma$, respectively. Furthermore, we rule out the presence of a strong temperature inversion near the IR photosphere -- predicted by GCMs to form temporarily during periapse passage -- based on the lack of obvious emission features throughout the observing window. Our study demonstrates the feasibility of studying hot Jupiter atmospheres using partial phase curves obtained with NIRSpec/G395H., Comment: 25 pages, 19 figures, 2 tables. Submitted to ApJ

Super-Earths orbiting M-dwarf stars may be the most common habitable planets in the Universe. However, their habitability is threatened by intense irradiation from their host stars, which drives the escape of water to space and can lead to surface desiccation. We present simulation results of a box model of water cycling between interior and atmosphere and loss to space, for terrestrial planets of mass 1--8 $M_\oplus$ orbiting in the habitable zone of a late M-dwarf. Energy-limited loss decreases with planetary mass, while diffusion-limited loss increases with mass. Depending on where it orbits in the habitable zone, a 1 $M_\oplus$ planet that starts with 3--8 Earth Oceans can end up with an Earth-like surface of oceans and exposed continents; for an 8 $M_\oplus$ super-Earth, that range is 3--12 Earth Oceans. Planets initialized with more water end up as waterworlds with no exposed continents, while planets that start with less water have desiccated surfaces by 5 Gyr. Since the mantles of terrestrial planets can hold much more water than is currently present in Earth's atmosphere, none of our simulations result in Dune planets -- such planets may be less common than previously thought. Further, more water becomes sequestered within the mantle for larger planets. A super-Earth at the inner edge of the habitable zone tends to end up as either a waterworld or with a desiccated surface; only a narrow range of initial water inventory yields an Earth-like surface., Comment: 12 pages, 5 figures; revisions submitted to The Astrophysical Journal

LHS 1140 b is the second-closest temperate transiting planet to the Earth with an equilibrium temperature low enough to support surface liquid water. At 1.730$\pm$0.025 R$_\oplus$, LHS 1140 b falls within the radius valley separating H$_2$-rich mini-Neptunes from rocky super-Earths. Recent mass and radius revisions indicate a bulk density significantly lower than expected for an Earth-like rocky interior, suggesting that LHS 1140 b could either be a mini-Neptune with a small envelope of hydrogen ($\sim$0.1% by mass) or a water world (9--19% water by mass). Atmospheric characterization through transmission spectroscopy can readily discern between these two scenarios. Here, we present two JWST/NIRISS transit observations of LHS 1140 b, one of which captures a serendipitous transit of LHS 1140 c. The combined transmission spectrum of LHS 1140 b shows a telltale spectral signature of unocculted faculae (5.8 $\sigma$), covering $\sim$20% of the visible stellar surface. Besides faculae, our spectral retrieval analysis reveals tentative evidence of residual spectral features, best-fit by Rayleigh scattering from an N$_2$-dominated atmosphere (2.3 $\sigma$), irrespective of the consideration of atmospheric hazes. We also show through Global Climate Models (GCM) that H$_2$-rich atmospheres of various compositions (100$\times$, 300$\times$, 1000$\times$solar metallicity) are ruled out to $>$10 $\sigma$. The GCM calculations predict that water clouds form below the transit photosphere, limiting their impact on transmission data. Our observations suggest that LHS 1140 b is either airless or, more likely, surrounded by an atmosphere with a high mean molecular weight. Our tentative evidence of an N$_2$-rich atmosphere provides strong motivation for future transmission spectroscopy observations of LHS 1140 b., Comment: 26 pages, 14 figures, 3 tables, accepted for publication in ApJL

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., Comment: 10 pages, 8 figures. Submitted to ApJ

The hot-Neptune desert is one of the most sparsely populated regions of the exoplanet parameter space, and atmosphere observations of its few residents can provide insights into how such planets have managed to survive in such an inhospitable environment. Here, we present transmission observations of LTT 9779 b, the only known hot-Neptune to have retained a significant H/He-dominated atmosphere, taken with JWST NIRISS/SOSS. The 0.6-2.85$\mu$m transmission spectrum shows evidence for muted spectral features, rejecting a perfectly flat line at >5$\sigma$. We explore water and methane-dominated atmosphere scenarios for LTT 9779 b's terminator, and retrieval analyses reveal a continuum of potential combinations of metallicity and cloudiness. Through comparisons to previous population synthesis works and our own interior structure modelling, we are able to constrain LTT 9779 b's atmosphere metallicity to 20-850x solar. Within this range of metallicity, our retrieval analyses prefer solutions with clouds at mbar pressures, regardless of whether the atmosphere is water- or methane-dominated -- though cloud-free atmospheres with metallicities >500x solar cannot be entirely ruled out. By comparing self-consistent atmosphere temperature profiles with cloud condensation curves, we find that silicate clouds can readily condense in the terminator region of LTT 9779 b. Advection of these clouds onto the day-side could explain the high day-side albedo previously inferred for this planet and be part of a feedback loop aiding the survival of LTT 9779 b's atmosphere in the hot-Neptune desert., Comment: Accepted for publication in ApJL