Planetary Climate Dynamics

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.

Abstract:

Spectroscopic characterization of rocky exoplanets with the James Webb Space Telescope has brought the origin and evolution of their atmospheres into the focus of exoplanet science. Time-evolved models of the feedback between interior and atmosphere are critical to predict and interpret these observations and link them to the solar system terrestrial planets. However, models differ in methodologies and input data, which can lead to significant differences in interpretation. In this paper, we present the experimental protocol of the Coupled atmospHere Interior modeL Intercomparison (CHILI) project. CHILI is an (exo)planet model intercomparison project within the Climates Using Interactive Suites of Intercomparisons Nested for Exoplanet Studies (CUISINES) framework, which aims to support a diverse set of multimodel intercomparison projects in the exoplanet community. The present protocol includes the initial set of participating magma ocean models, divided into evolutionary and static models, and two types of test categories, one focused on solar system planets (Earth and Venus) and the other on exoplanets orbiting low-mass M dwarfs. Both test categories aim to quantify the evolution of key markers of the links between planetary atmospheres and interiors over geological timescales. The proposed tests would allow us to quantify and compare the differences between coupled atmosphere–interior models used by the exoplanet and planetary science communities. Results from the proposed tests will be published in dedicated follow-up papers. To encourage the community to join this comparison effort, and as an example, we present initial test results for the early Earth and TRAPPIST-1 b, conducted with models differing in the treatment of energy transport in the planetary interior and atmosphere, surface boundary layer, geochemistry, and in- and outgassing of volatile compounds.

Abstract:

ABSTRACT While Earth locks much of its carbon in its crust as carbonates, Venus retains a comparable carbon inventory almost entirely in its atmosphere as CO$_2$. On Earth, the geological carbon cycle that has produced this vast crustal carbonate inventory is regulated by biology, liquid water, and plate tectonics, which together have stabilized climate over geological time-scales. Venus presently lacks all these processes. We test whether Venus’s massive CO$_2$ atmosphere is diagnostic of a specific evolutionary pathway by quantifying three routes: primary magma-ocean outgassing, secondary volcanic degassing in a stagnant-lid regime, and remobilization of crustal carbonates after climate destabilization. Using a coupled climate–weathering framework, we find that a past habitable Venus could have stored $\sim$20 bar of CO$_2$ as crustal carbonates. Following the transition to runaway conditions, crustal heating releases this reservoir over tens of Myr. In stagnant-lid secondary-degassing models with a MORB-like mantle, outgassing reaches only $\sim$25 bar CO$_2$, limited by progressive mantle volatile depletion. However, Venus-like inventories can be achieved through: (i) magmatic carbon enrichment, (ii) increased magmatic delivery to the surface (high extrusion or melt production), and (iii) the recycling of undegassed carbon back into the planet’s interior. Primary magma-ocean outgassing can generate $\gt 10^2$ bar CO$_2$, but the retained fraction after early escape remains uncertain. Ultimately, a Venus-like massive CO$_2$ atmosphere is an equifinal outcome and does not uniquely diagnose a temperate past.