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A carbon-rich exoplanet The transiting 'hot Jupiter' WASP-12b orbits a star slightly hotter than the Sun in a circular orbit at a distance of only 0.023 astronomical units (AU), making it one of the hottest exoplanets known. An analysis of dayside multi-wavelength photometry of WASP-12b reveals a carbon-rich atmosphere abundant in carbon monoxide. Compared with model predictions, the atmosphere is depleted in water vapour and enhanced in methane content by two orders of magnitude. In addition, the absence of a strong thermal inversion or a prominent stratosphere challenges existing theories about the atmospheres of such exoplanets. A primordial carbon-to-oxygen ratio (C/O) greater than 0.8 in an exoplanet causes a carbide-dominated interior, as opposed to the silicate-dominated composition found on Earth; the atmospheres also can differ from those in the Solar System. The solar C/O is 0.54. This study reports an analysis of spectra from the transiting hot Jupiter WASP-12b that reveals that C/O>1 in its atmosphere, based upon the observed concentrations of the prominent molecules CO, CH 4 and H 2 O. The carbon-to-oxygen ratio (C/O) in a planet provides critical information about its primordial origins and subsequent evolution. A primordial C/O greater than 0.8 causes a carbide-dominated interior, as opposed to the silicate-dominated composition found on Earth 1 ; the atmosphere can also differ from those in the Solar System 1 , 2 . The solar C/O is 0.54 (ref. 3 ). Here we report an analysis of dayside multi-wavelength photometry 4 , 5 of the transiting hot-Jupiter WASP-12b (ref. 6 ) that reveals C/O ≥ 1 in its atmosphere. The atmosphere is abundant in CO. It is depleted in water vapour and enhanced in methane, each by more than two orders of magnitude compared to a solar-abundance chemical-equilibrium model at the expected temperatures. We also find that the extremely irradiated atmosphere ( T  > 2,500 K) of WASP-12b lacks a prominent thermal inversion (or stratosphere) and has very efficient day–night energy circulation. The absence of a strong thermal inversion is in stark contrast to theoretical predictions for the most highly irradiated hot-Jupiter atmospheres 7 , 8 , 9 .

Measurements of a precursor to a low-mass white-dwarf star reveal that such white-dwarf stars probably had a thick hydrogen envelope, which was lost by irradiation or shell flashes in the case of rapidly cooling white-dwarf stars. A pulsating star in red-to-white transition Before becoming low-mass white dwarfs, stripped red-giant stars evolve at nearly constant luminosity towards higher effective temperatures. The system known as J0247-25 was recently found to be a binary in which a star in this unusual evolutionary state (J0247-25B) is totally eclipsed by an apparently normal A-type star (J0247-25A). New spectroscopic and photometric observations have been used to derive precise astrophysical parameters for both stars. The data fit models in which the hotter white-dwarf precursor has a thick hydrogen envelope. This suggests that very cool low-mass white dwarfs have lost their thick hydrogen envelopes by irradiation from pulsar companions or by episodes of unstable hydrogen fusion (shell flashes). The discovery of pulsations in J0247-25B opens up new observational opportunities for the study of the structure of a low-mass white dwarf. Low-mass white-dwarf stars are the remnants of disrupted red-giant stars in binary millisecond pulsars 1 and other exotic binary star systems 2 , 3 , 4 . Some low-mass white dwarfs cool rapidly, whereas others stay bright for millions of years because of stable fusion in thick surface hydrogen layers 5 . This dichotomy is not well understood, so the potential use of low-mass white dwarfs as independent clocks with which to test the spin-down ages of pulsars 6 , 7 or as probes of the extreme environments in which low-mass white dwarfs form 8 , 9 , 10 cannot fully be exploited. Here we report precise mass and radius measurements for the precursor to a low-mass white dwarf. We find that only models in which this disrupted red-giant star has a thick hydrogen envelope can match the strong constraints provided by our data. Very cool low-mass white dwarfs must therefore have lost their thick hydrogen envelopes by irradiation from pulsar companions 11 , 12 or by episodes of unstable hydrogen fusion (shell flashes). We also find that this low-mass white-dwarf precursor is a type of pulsating star not hitherto seen. The observed pulsation frequencies are sensitive to internal processes that determine whether this star will undergo shell flashes.

The EBLM project aims to characterise very-low-mass stars that are companions to solar-type stars in eclipsing binaries. We describe the history and motivation for this project, the methodology we use to obtain the precise mass, radius, and effective temperature estimates for very-low-mass M dwarfs, and review the results of the EBLM study and those from related projects. We show that radius inflation in fully convective stars is a more subtle effect than what was previously thought based on less precise measurements, i.e., the mass–radius–effective temperature relations we observe for fully convective stars in single-line eclipsing binaries show reasonable agreement with the theoretical models, particularly if we account for the M-dwarf metallicity, as inferred from the analysis of the primary star spectrum.

Circumbinary planets, those that orbit around both stars of a central binary star system, challenge our understanding of planet formation. With only 12 binary systems known to host circumbinary planets, identifying more of these planets, along with their physical properties, could help to discern some of the physical processes that govern planet formation. Here we analyse radial-velocity data obtained by the HARPS and ESPRESSO spectrographs and report the detection of BEBOP-1 c, a gas giant planet with a mass of 65.2 ± 11.8 Earth masses (M⊕) orbiting around both stars of an eclipsing binary star system with a period of 215.5 ± 3.3 days. The system TOI-1338, hereafter referred to as BEBOP-1, which also hosts the smaller and inner transiting planet TOI-1338 b, is only the second confirmed multiplanetary circumbinary system. We do not detect TOI-1338 b with radial-velocity data alone, and we can place an upper limit on its mass of 21.8 M⊕ with 99% confidence. TOI-1338 b is amenable to atmospheric characterization using JWST, so the BEBOP-1 system has the potential to act as a benchmark for circumbinary exo-atmospheric studies.The radial-velocity technique could detect a small gas giant orbiting a binary star and determine its mass: 65.2 ± 11.8 Earth masses. The system also hosts a smaller inner planet, making it one of the few known multiplanetary circumbinary systems.

Stars appear darker at their limbs than at their disk centres because at the limb we are viewing the higher and cooler layers of stellar photospheres. Yet, limb darkening derived from state-of-the-art stellar atmosphere models systematically fails to reproduce recent transiting exoplanet light curves from the Kepler, TESS and JWST telescopes—stellar brightness obtained from measurements drops less steeply towards the limb than predicted by models. Previous models assumed stellar atmospheres devoid of magnetic fields. Here we use stellar atmosphere models computed with the three-dimensional radiative magnetohydrodynamic code MURaM to show that a small-scale concentration of magnetic fields on the stellar surface affects limb darkening at a level that allows us to explain the observations. Our findings provide a way forward to improve the determination of exoplanet radii and especially the transmission spectroscopy analysis for transiting planets, which relies on a very accurate description of stellar limb darkening from the visible to the infrared. Furthermore, our findings imply that limb darkening allows estimates of the small-scale magnetic field strength on stars with transiting planets. An outstanding discrepancy between observations and models of stellar limb darkening is resolved here by the inclusion of stellar surface magnetism in models. This will enable an improved characterization of transiting exoplanets.

Exoplanets transiting bright nearby stars are key objects for advancing our knowledge of planetary formation and evolution. The wealth of photons from the host star gives detailed access to the atmospheric, interior and orbital properties of the planetary companions. ν 2 Lupi (HD 136352) is a naked-eye ( V  = 5.78) Sun-like star that was discovered to host three low-mass planets with orbital periods of 11.6, 27.6 and 107.6 d via radial-velocity monitoring 1 . The two inner planets (b and c) were recently found to transit 2 , prompting a photometric follow-up by the brand new Characterising Exoplanets Satellite (CHEOPS). Here, we report that the outer planet d is also transiting, and measure its radius and mass to be 2.56 ± 0.09  R ⊕ and 8.82 ± 0.94  M ⊕ , respectively. With its bright Sun-like star, long period and mild irradiation (~5.7 times the irradiation of Earth), ν 2 Lupi d unlocks a completely new region in the parameter space of exoplanets amenable to detailed characterization. We refine the properties of all three planets: planet b probably has a rocky mostly dry composition, while planets c and d seem to have retained small hydrogen–helium envelopes and a possibly large water fraction. This diversity of planetary compositions makes the ν 2 Lupi system an excellent laboratory for testing formation and evolution models of low-mass planets. Three planets orbit the Sun-like star ν 2 Lupi. CHEOPS data show that all of them are transiting and show remarkable diversity. In particular, dry and gas-poor inner planet b has experienced extensive atmospheric loss, while planets c and d are water rich and have a small gaseous envelope of primordial origin.

Gas giants transiting bright nearby stars provide crucial insights into planetary system formation and evolution mechanisms. Most of these planets show certain average characteristics, serving as benchmarks for our understanding of planetary systems. However, outliers like the planet we present in this study, WASP-193 b, offer unique opportunities to explore unconventional formation and evolution processes. This planet completes an orbit around its V -band-magnitude 12.2 F9 main-sequence host star every 6.25 days. Our analyses found that WASP-193 b has a mass of 0.139 ± 0.029  M J and a radius of 1.464 ± 0.058  R J , translating into an extremely low density of 0.059 ± 0.014g cm −3 , at least one order of magnitude less than standard gas giants like Jupiter. Typical gas giants such as Jupiter have densities that range between 0.2 g cm −3 and 2 g cm −3 . The combination of its large transit depth (1.4%), extremely low density, high-equilibrium temperature (1,254 ± 31 K) and the infrared brightness of its host star ( K -band magnitude 10.7) makes WASP-193 b an exquisite target for characterization by transmission spectroscopy (transmission spectroscopy metric ~600). One single JWST transit observation would yield detailed insights into its atmospheric properties and planetary mass, providing a unique window to explore the mechanisms behind its exceptionally low density and shed light on giant planets’ diverse nature. Precise mass and radius measurements of giant planet WASP-193 b find an extremely low density of 0.059 ± 0.014 g cm −3 . Current evolutionary models cannot fully explain such a low density, but the extended atmosphere makes WASP-193 b very suitable for high-precision characterization via JWST.

One class of binary stars, in which white dwarfs accrete material from low-mass companions, has long been predicted, but their dimness has made observations difficult. Evidence that they exist now comes from the Sloan Digital Sky Survey.

The detection of sodium absorption during primary transit implies the presence of an atmosphere around an extrasolar planet. WASP-17b (Anderson et al. 2010a) is the least dense known planet, with a radius twice that of Jupiter. It orbits an F6-type star, and its low gravity gives its atmosphere a very large scale height. The sodium transit depth is expected to be 4.1 – 5.2 times deeper than for HD 209458b (Seager & Sasselov 2000). We obtained 24 spectra with the GIRAFFE spectrograph on the VLT, 8 during transit. We measured the flux in the sodium doublet at 5889.95 Å and 5895.92 Å using bandpasses 0.75, 1.5, 3.0 and 6.0 Å. We find a transit depth of 0.55±0.13% at 1.5 Å (4.3σ). WASP-17b therefore has an atmosphere which is depleted in sodium compared to predictions.

Planetary systems orbiting close binaries are valuable testing grounds for planet formation and migration models. More detections with good mass measurements are needed. We present a new planet discovered during the BEBOP survey for circumbinary exoplanets using radial velocities. We use data taken with the SOPHIE spectrograph at the Observatoire de Haute-Provence, and perform a spectroscopic analysis to obtain high precision radial velocities. This planet is the first radial velocity detection of a previously unknown circumbinary system. The planet has a mass of \\(0.56\\) \\(M_{Jup}\\) and orbits its host binary in 550 days with an eccentricity of 0.25. Compared to most of the previously known circumbinary planets, BEBOP-3b has a long period (relative to the binary) and a high eccentricity. There also is a candidate outer planet with a \\(\\sim1400\\) day orbital period. We test the stability of potential further candidate signals inside the orbit of BEBOP-3b, and demonstrate that there are stable orbital solutions for planets near the instability region which is where the Kepler circumbinary planets are located. We also use our data to obtain independent dynamical masses for the two stellar components of the eclipsing binary using High Resolution Cross-Correlation Spectroscopy (HRCCS), and compare those results to a more traditional approach, finding them compatible with one another.