Explore the vast range of titles available.

Observations of transiting gas giant exoplanets have revealed a pervasive depletion of methane 1 – 4 , which has only recently been identified atmospherically 5 , 6 . The depletion is thought to be maintained by disequilibrium processes such as photochemistry or mixing from a hotter interior 7 – 9 . However, the interiors are largely unconstrained along with the vertical mixing strength and only upper limits on the CH 4 depletion have been available. The warm Neptune WASP-107b stands out among exoplanets with an unusually low density, reported low core mass 10 , and temperatures amenable to CH 4 , though previous observations have yet to find the molecule 2 , 4 . Here we present a JWST-NIRSpec transmission spectrum of WASP-107b that shows features from both SO 2 and CH 4 along with H 2 O, CO 2 , and CO. We detect methane with 4.2 σ significance at an abundance of 1.0 ± 0.5 ppm, which is depleted by 3 orders of magnitude relative to equilibrium expectations. Our results are highly constraining for the atmosphere and interior, which indicate the envelope has a super-solar metallicity of 43 ± 8 × solar, a hot interior with an intrinsic temperature of T int  = 460 ± 40 K, and vigorous vertical mixing which depletes CH 4 with a diffusion coefficient of K zz  = 10 11.6±0.1  cm 2  s −1 . Photochemistry has a negligible effect on the CH 4 abundance but is needed to account for the SO 2 . We infer a core mass of 11.5 − 3.6 + 3.0 M ⊕ , which is much higher than previous upper limits 10 , releasing a tension with core-accretion models 11 . Observations of the warm Neptune WASP-107b show that the planet has a hot interior with an intrinsic temperature of about 460 K.

Two exoplanet atmospheres examined This paper reports Hubble Space Telescope observations of the inner two of three Earth-sized exoplanets that were recently discovered close to the habitable zone of the nearby ultracool dwarf star TRAPPIST-1. The combined transmission spectrum of TRAPPIST-1 b and c was obtained during their simultaneous transits on 4 May 2016. The lack of features in the combined spectrum effectively rules out cloud-free hydrogen-dominated atmospheres for each planet, but they could have a variety of other types of atmosphere, from one consisting mainly of cloud-free water vapour to a Venus-like atmosphere. Three Earth-sized exoplanets were recently discovered close to the habitable zone 1 , 2 of the nearby ultracool dwarf star TRAPPIST-1 (ref. 3 ). The nature of these planets has yet to be determined, as their masses remain unmeasured and no observational constraint is available for the planetary population surrounding ultracool dwarfs, of which the TRAPPIST-1 planets are the first transiting example. Theoretical predictions span the entire atmospheric range, from depleted to extended hydrogen-dominated atmospheres 4 , 5 , 6 , 7 , 8 . Here we report observations of the combined transmission spectrum of the two inner planets during their simultaneous transits on 4 May 2016. The lack of features in the combined spectrum rules out cloud-free hydrogen-dominated atmospheres for each planet at ≥10 σ levels; TRAPPIST-1 b and c are therefore unlikely to have an extended gas envelope as they occupy a region of parameter space in which high-altitude cloud/haze formation is not expected to be significant for hydrogen-dominated atmospheres 9 . Many denser atmospheres remain consistent with the featureless transmission spectrum—from a cloud-free water-vapour atmosphere to a Venus-like one.

We report on James Webb Space Telescope (JWST) commissioning observations of the transiting exoplanet HAT-P-14 b, obtained using the Bright Object Time Series (BOTS) mode of the NIRSpec instrument with the G395H/F290LP grating/filter combination (3–5 μ m). While the data were used primarily to verify that the NIRSpec BOTS mode is working as expected, and to enable it for general scientific use, they yield a precise transmission spectrum which we find is featureless down to the precision level of the instrument, consistent with expectations given HAT-P-14 b’s small scale-height and hence expected atmospheric features. The exquisite quality and stability of the JWST/NIRSpec transit spectrum—almost devoid of any systematic effects—allowed us to obtain median uncertainties of 50–60 ppm in this wavelength range at a resolution of R = 100 in a single exposure, which is in excellent agreement with pre-flight expectations and close to the (or at the) photon-noise limit for a J = 9.094, F-type star like HAT-P-14. These observations showcase the ability of NIRSpec/BOTS to perform cutting-edge transiting exoplanet atmospheric science, setting the stage for observations and discoveries to be made in Cycle 1 and beyond.

The critical first step in the search for life on exoplanets over the next decade is to determine whether rocky planets transiting small M-dwarf stars possess atmospheres and, if so, what processes sculpt them over time. Because of its broad wavelength coverage and improved resolution compared with previous instruments, spectroscopy with the James Webb Space Telescope (JWST) offers a new capability to detect and characterize the atmospheres of Earth-sized, M-dwarf planets. Here we use the JWST to independently validate the discovery of LHS 475 b, a warm (586 K), 0.99 Earth-radius exoplanet, interior to the habitable zone, and report a precise 2.9–5.3 μm transmission spectrum using the Near Infrared Spectrograph G395H instrument. With two transit observations, we rule out primordial hydrogen-dominated and cloudless pure methane atmospheres. Thus far, the featureless transmission spectrum remains consistent with a planet that has a high-altitude cloud deck (similar to Venus), a tenuous atmosphere (similar to Mars) or no appreciable atmosphere at all (akin to Mercury). There are no signs of stellar contamination due to spots or faculae. Our observations show that the JWST has the requisite sensitivity to constrain the secondary atmospheres of terrestrial exoplanets with absorption features <50 ppm, and that our current atmospheric constraints speak to the nature of the planet itself, rather than instrumental limits.The warm Earth-sized planet LHS 475 b is validated and characterized with two transits observed by the JWST. The absence of evident spectroscopic features excludes a substantial hydrogen envelope and indicates that LHS 475 b has either little or no atmosphere or an optically thick cloud deck at high altitudes.

Numerous Solar System atmospheres possess photochemically generated hazes, including the characteristic organic hazes of Titan and Pluto. Haze particles substantially impact atmospheric temperature structures and may provide organic material to the surface of a world, potentially affecting its habitability. Observations of exoplanet atmospheres suggest the presence of aerosols, especially in cooler (<800 K), smaller (<0.3× Jupiter’s mass) exoplanets. It remains unclear whether the aerosols muting the spectroscopic features of exoplanet atmospheres are condensate clouds or photochemical hazes 1 – 3 , which is difficult to predict from theory alone 4 . Here, we present laboratory haze simulation experiments that probe a broad range of atmospheric parameters relevant to super-Earth- and mini-Neptune-type planets 5 , the most frequently occurring type of planet in our galaxy 6 . It is expected that photochemical haze will play a much greater role in the atmospheres of planets with average temperatures below 1,000 K (ref. 7 ), especially those planets that may have enhanced atmospheric metallicity and/or enhanced C/O ratios, such as super-Earths and Neptune-mass planets 8 – 12 . We explored temperatures from 300 to 600 K and a range of atmospheric metallicities (100×, 1,000× and 10,000× solar). All simulated atmospheres produced particles, and the cooler (300 and 400 K) 1,000× solar metallicity (‘H 2 O-dominated’ and CH 4 -rich) experiments exhibited haze production rates higher than our standard Titan simulation (~10 mg h –1 versus 7.4 mg h –1 for Titan 13 ). However, the particle production rates varied greatly, with measured rates as low as 0.04 mg h –1 (for the case with 100× solar metallicity at 600 K). Here, we show that we should expect great diversity in haze production rates, as some—but not all—super-Earth and mini-Neptune atmospheres will possess photochemically generated haze. Laboratory experiments explore aerosol formation at conditions that can be found on planets with radii between Earth and Neptune that do not exist in the Solar System but are common elsewhere. Photochemically generated hazes are produced in most cases.

Magnificent Failures Brown dwarfs are so-called failed stars that have insufficient mass to sustain nuclear reactions but are too massive to be planets. From this in-between position, brown dwarfs offer unique insights into the nature and origins of both stars and planets. Until now it has not been possible to measure the fundamental physical properties of brown dwarfs directly. But with the discovery of two young brown dwarfs in an eclipsing binary system in the Orion Nebula star-forming region, it has been possible to measure the mass and radius of two in one go. Surprisingly, the less-massive brown dwarf is the hotter of the pair; a finding that runs contrary to the predictions of all current theoretical models of coeval brown dwarfs. This might mean that the two brown dwarfs did not form at the same time, but got together in the recent past. The discovery of a brown-dwarf eclipsing binary system presents a puzzle, as despite both objects having large radii in accordance with current theory the less-massive brown dwarf is the hotter of the pair, contrary to theoretical predictions. Brown dwarfs are considered to be ‘failed stars’ in the sense that they are born with masses between the least massive stars (0.072 solar masses, M ⊙ ) 1 and the most massive planets (∼0.013 M ⊙ ) 2 ; they therefore serve as a critical link in our understanding of the formation of both stars and planets 3 . Even the most fundamental physical properties of brown dwarfs remain, however, largely unconstrained by direct measurement. Here we report the discovery of a brown-dwarf eclipsing binary system, in the Orion Nebula star-forming region, from which we obtain direct measurements of mass and radius for these newly formed brown dwarfs. Our mass measurements establish both objects as brown dwarfs, with masses of 0.054 ± 0.005 M ⊙ and 0.034 ± 0.003 M ⊙ . At the same time, with radii relative to the Sun's of 0.669 ± 0.034 R ⊙ and 0.511 ± 0.026 R ⊙ , these brown dwarfs are more akin to low-mass stars in size. Such large radii are generally consistent with theoretical predictions for young brown dwarfs in the earliest stages of gravitational contraction 4 , 5 . Surprisingly, however, we find that the less-massive brown dwarf is the hotter of the pair; this result is contrary to the predictions of all current theoretical models of coeval brown dwarfs.

Photochemical hazes are important opacity sources in temperate exoplanet atmospheres, hindering current observations from characterizing exoplanet atmospheric compositions. The haziness of an atmosphere is determined by the balance between haze production and removal. However, the material-dependent removal physics of the haze particles are currently unknown under exoplanetary conditions. Here we provide experimentally measured surface energies for a grid of temperate exoplanet hazes to characterize haze removal in exoplanetary atmospheres. We found large variations of surface energies for hazes produced under different energy sources, atmospheric compositions and temperatures. The surface energies of the hazes were found to be the lowest around 400 K for the cold plasma samples, leading to the lowest removal rates. We show a suggestive correlation between haze surface energy and atmospheric haziness with planetary equilibrium temperature. We hypothesize that habitable-zone exoplanets could be less hazy, as they would possess high-surface-energy hazes that can be removed efficiently. Photochemical hazes in exoplanet atmospheres work as opacity barriers, hindering characterization of the atmospheres themselves. Here laboratory experiments quantify the haze surface energies that factor into the removal of hazes from atmospheres, which, when added to existing data on haze production, give a greater understanding of haze properties.

The questions of how planets form and how common Earth-like planets are can be addressed by measuring the distribution of exoplanet masses and orbital periods. We report the occurrence rate of close-in planets (with orbital periods less than 50 days), based on precise Doppler measurements of 166 Sun-like stars. We measured increasing planet occurrence with decreasing planet mass (M). Extrapolation of a power-law mass distribution fitted to our measurements, df/dlogM = 0.39 M⁻⁰.⁴⁸, predicts that 23% of stars harbor a close-in Earth-mass planet (ranging from 0.5 to 2.0 Earth masses). Theoretical models of planet formation predict a deficit of planets in the domain from 5 to 30 Earth masses and with orbital periods less than 50 days. This region of parameter space is in fact well populated, implying that such models need substantial revision.

Near‐ultraviolet spectroscopic data obtained with theHubble Space TelescopeSTIS (Space Telescope Imaging Spectrograph) instrument on the dMe flare star YZ Canis Minoris (YZ CMi) were analyzed. Flare and quiet intervals were identified from the broadband near‐UV light curve, and the spectrum of each flare was separately extracted. Mgiiand Feiiline profiles show similar behavior during the flares. Two large flares allowed time‐resolved spectra to be analyzed, revealing a very broad component to the Mgii kline profile in at least one flare spectrum (F9b). If interpreted as a velocity, this component requires chromospheric material to be moving with FWHM ∼ 250 km s−1, implying kinetic energy far in excess of the radiative energy. The Mgii kflare line profiles were compared to recent radiative hydrodynamic models of flare atmospheres undergoing electron beam heating. The models successfully predict red enhancements in the line profile, with a typical velocity of a few km s−1, but do not reproduce the flares showing blue enhancements, or the strongly broadened line observed in flare F9b. A more complete calculation of redistribution into the line wings, including the effect of collisions with the electron beam, may resolve the origin of the excess line broadening.

The James Webb Space Telescope (JWST) will likely revolutionize transiting exoplanet atmospheric science, due to a combination of its capability for continuous, long duration observations and its larger collecting area, spectral coverage, and spectral resolution compared to existing space-based facilities. However, it is unclear precisely how well JWST will perform and which of its myriad instruments and observing modes will be best suited for transiting exoplanet studies. In this article, we describe a prefatory JWST Early Release Science (ERS) Cycle 1 program that focuses on testing specific observing modes to quickly give the community the data and experience it needs to plan more efficient and successful transiting exoplanet characterization programs in later cycles. We propose a multi-pronged approach wherein one aspect of the program focuses on observing transits of a single target with all of the recommended observing modes to identify and understand potential systematics, compare transmission spectra at overlapping and neighboring wavelength regions, confirm throughputs, and determine overall performances. In our search for transiting exoplanets that are well suited to achieving these goals, we identify 12 objects (dubbed \"community targets\") that meet our defined criteria. Currently, the most favorable target is WASP-62b because of its large predicted signal size, relatively bright host star, and location in JWST's continuous viewing zone. Since most of the community targets do not have well-characterized atmospheres, we recommend initiating preparatory observing programs to determine the presence of obscuring clouds/hazes within their atmospheres. Measurable spectroscopic features are needed to establish the optimal resolution and wavelength regions for exoplanet characterization. Other initiatives from our proposed ERS program include testing the instrument brightness limits and performing phase-curve observations. The latter are a unique challenge compared to transit observations because of their significantly longer durations. Using only a single mode, we propose to observe a full-orbit phase curve of one of the previously characterized, short-orbital-period planets to evaluate the facility-level aspects of long, uninterrupted time-series observations.