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Abstract:

Planets with nonzero obliquity and/or orbital eccentricity experience seasonal variations of stellar irradiation at local latitudes. The extent of the atmospheric response can be crudely estimated by the ratio of the orbital timescale to the atmospheric radiative timescale. Given a set of atmospheric parameters, we show that this ratio depends mostly on the stellar properties and is independent of orbital distance and planetary equilibrium temperature. For Jupiter-like atmospheres, this ratio is ≪1 for planets around very low mass M dwarfs and ≳1 when the stellar mass is greater than about 0.6 solar mass. Complications can arise from various factors, including varying atmospheric metallicity, clouds, and atmospheric dynamics. Given the eccentricity and obliquity, the seasonal response is expected to be systematically weaker for gaseous exoplanets around low-mass stars and stronger for those around more massive stars. The amplitude and phase lag of atmospheric seasonal variations as a function of host stellar mass are quantified by idealized analytic models. At the infrared emission level in the photosphere, the relative amplitudes of thermal flux and temperature perturbations are negligible, and their phase lags are closed to −90° for Jupiter-like planets around very low mass stars. The relative amplitudes and phase lags increase gradually with increasing stellar mass. With a particular stellar mass, the relative amplitude and phase lag decrease from low- to high-infrared optical depth. We also present numerical calculations for a better illustration of the seasonal behaviors. Last, we discuss implications for the atmospheric circulation and future atmospheric characterization of exoplanets in systems with different stellar masses.

Abstract:

Tidally locked lava planets are hot, rocky worlds on close-in orbits with a permanent molten dayside. With JWST, their surfaces and atmospheres are beginning to be revealed. This work investigates three-dimensional (3D) magma ocean dynamics, derives scaling laws for the resulting ocean heat transport, and predicts its detectability. For the first time, the ocean circulation driven by the intense momentum and mass exchanges with the supersonic atmosphere is considered in addition to that by thermal forcing. The wind forcing turns out to overwhelmingly dominate the other two mechanisms, driving ocean currents reaching ∼100 m s^−1 and greatly expanding the latitudinal extent of the Matsuno–Gill response. Despite these extreme flow speeds, scaling analysis and 3D simulations consistently demonstrate that magma ocean circulation alone does not produce an observable hot-spot offset. This inefficiency arises because basin geometry and circulation structure fundamentally constrain zonal heat redistribution, suppressing large-scale longitudinal transport even under vigorous flow.

Abstract:

Ultra-hot Jupiters (UHJs) present extreme atmospheric phenomena not found in the solar system. These planets’ daysides experience strong temperature inversions, molecular species (including H2) dissociate, and magnetism effects disrupt atmospheric circulation. On their nightsides, H2 can recombine and clouds may form. Spectroscopic phase curves allow us to measure these spatially inhomogeneous conditions, which can then be interpreted with three-dimensional (3D) models. In this work, we compare the JWST Near Infrared Imager and Slitless Spectrograph (or NIRISS) spectroscopic phase curve of the UHJ WASP-121 b to state-of-the-art 3D models with varying modeling assumptions, including the aforementioned physical phenomena. We demonstrate the importance of accurately accounting for the planet’s radius when comparing data and models, as it changes the implied overall planetary emission. We find that the 3D models predict planetary emission that is ∼12% higher than observed, contributing to the continued tension between measured and predicted hot Jupiter albedos. We identify multiple lines of evidence confirming a strong source of drag operating in this planet’s atmosphere. In addition, the nightside emission spectrum is devoid of strong absorption features, which may be best explained by nightside clouds. One feature of the dataset that is not reproduced by the 3D models is a trend toward increasingly eastward phase offsets at wavelengths shorter than ∼1.4 μm. This result is inconsistent with reflection from dayside clouds, nor can it be explained by removing atmospheric opacity sources. Our analysis highlights the complexities involved in generating 3D models and interpreting observations of UHJs in the JWST era.

Abstract:

We present high-precision chemical abundances for 25 FGK-type stars hosting exoplanets observed in JWST Cycle 3 programs and all Guaranteed Time Observations and Director’s Discretionary Time programs from Cycles 1–3, based on high-resolution, high-signal-to-noise ratio optical spectra from ground-based telescopes. Using a strictly differential, line-by-line analysis relative to the Sun, we derive homogeneous stellar parameters and abundances for 19 elements with an atomic number Z ≤ 30. The sample spans a wide range of stellar properties, with [Fe/H] = −0.6 to +0.4 dex and effective temperatures between 4700 and 6600 K, and includes hosts of terrestrial and giant planets as well as multiplanet systems. We refine carbon and sulfur abundances in cool dwarfs using a spectral synthesis, mitigating systematics from line blending. Several chemically interesting systems are identified, including mildly α-enhanced metal-poor stars and multiplanet hosts with elevated [C/O]. Using isochrone ages, we derive empirical Galactic chemical evolution (GCE) relations and examine condensation temperature (Tcond) trends before and after a GCE correction. The Tcond slopes show no dependence on stellar or planetary properties, indicating that they reflect a mixture of multiple mechanisms, with planet-related signatures entangled in GCE and stellar evolution effects. Thus, Tcond trends require careful interpretation. Several systems with significantly positive or negative Tcond slopes are identified. Together with forthcoming JWST atmospheric measurements, this homogeneous stellar abundance catalog provides a basis for probing star–planet chemical connections and planet formation pathways.

Abstract:

Hot Jupiters have temperature gradients of several hundreds of degrees between their permanent daysides and nightsides. Such a strong gradient creates winds with speeds of the order of kilometres per second, which advect chemical species over the whole planet. When this transport is faster than the time needed for chemical species to react, it holds back the chemical equilibration of the atmospheric carbon reservoir, which would otherwise transition from CO on the dayside to CH4 on the nightside. Direct evidence of this process has remained elusive so far, as it is often degenerate with other atmospheric processes, such as vertical mixing or non-stellar elemental abundances. Here we present observational evidence for such a fast day-to-night horizontal transport of chemical species by observing the full 18-h orbit of the exoplanet NGTS-10A b with the JWST/NIRSpec instrument. We show that the carbon chemistry is dominated by CO in both the dayside and the nightside of the planet, with a strong depletion of CH4 on the nightside compared with expectations from chemical equilibrium. By measuring the atmospheric abundances of all the main carbon and oxygen molecules, we further demonstrate that the lack of CH4 on the planetary nightside cannot be attributed to non-solar elemental abundances or to vertical mixing mechanisms and must, therefore, be due to fast horizontal transport. Our study shows the fundamental role that atmospheric transport plays in shaping the distribution of chemical species on exoplanet atmospheres.