Planetary Climate Dynamics

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:

Sub-Neptunes are the most common type of detected exoplanet, yet their observed masses and radii are degenerate with several interior structures. One possibility is that sub-Neptunes have silicate/iron interiors and H-dominated atmospheres ( < 3.8 g mol), i.e., they are ‘gas dwarfs’. If gas dwarfs have molten interiors, interactions between their magma oceans and atmospheres will produce distinct observational signatures. These signatures may break the degeneracy in interior structure, while providing insight into their interior processes, history, and population trends. We expect all such planets are born molten, but under what conditions do they remain molten today? We use the coupled interior-climate evolution model, proteus, to estimate the ‘solidification shoreline’: the instellation flux boundary (as a function of stellar ) that separates molten gas dwarfs from solidified ones. Our results show that 98 per cent of detected sub-Neptunes occupy a region of parameter space consistent with their having permanent magma oceans, if they are gas dwarfs. While mantle and bulk volatile C/H ratio both influence magma ocean cooling, planets with oxidizing mantles and carbon-rich atmospheres are likely to have high mean-molecular weight atmospheres ( > 3.8 g mol) and are thus outside the scope of this study. Therefore, most detected sub-Neptunes, if they are gas dwarfs, have permanent magma oceans. This result motivates further research into the interactions between molten interiors and overlying atmospheres, and campaigns to identify unambiguous signatures of these interactions.

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:

Abstract The impact of anthropogenic aerosols on the mean, spatial, and temporal distribution of precipitation remains a persistent source of uncertainty in climate research. In particular, absorbing aerosols are known to influence cloud formation and precipitation in ways that are not yet fully understood. On average, warming induced by absorbing aerosols is balanced by reduced latent heating from precipitation, so the atmospheric energy budget constrains mean precipitation. This constraint does not apply to spatial or temporal patterns, making the impact of absorbing aerosols on these aspects more uncertain. A recent idealized study suggests that absorbing aerosols can trigger a transition to episodic precipitation, where rainfall occurs in intense, short‐lived events followed by extended dry periods. This transition resembles a previously reported shift under hothouse climate conditions. Specifically, lower tropospheric radiative heating from absorbing aerosols decouples the lower and upper troposphere, suppressing convection for multiple days. During these dry periods, instability builds up until a strong rain event occurs. In this paper, we build on this previous work to further investigate the effects of absorbing aerosols on precipitation characteristics and extremes. We conduct a hierarchy of model simulations that incorporate online aerosol–radiation coupling, the diurnal cycle of solar radiation, convective aggregation in a large‐domain, and large‐scale tropical circulation in a mock Walker simulation. Our results show that the transition to episodic precipitation events under absorbing aerosol perturbation is robust and occurs across all model configurations. We also examine the role of diurnal solar radiation variations and large‐scale circulation in shaping this transition.