Planetary Climate Dynamics

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Volatile-rich evolution of molten super-Earth L 98-59 d

Nature Astronomy Springer Science and Business Media LLC (2026)

Authors:

Harrison Nicholls, Tim Lichtenberg, Richard D Chatterjee, Claire Marie Guimond, Emma Postolec, Raymond T Pierrehumbert

Abstract:

Abstract Small, low-density exoplanets are sculpted by strong stellar irradiation, but their primordial compositions and subsequent evolution are still unknown. Two often-considered scenarios hold that they formed with rocky interiors and H 2 –He atmospheres (‘gas dwarfs’) or alternatively with bulk compositions dominated by H 2 O phases (‘water worlds’). Here we constrain the possible range of evolutionary histories linking the birth conditions of low-density super-Earth L 98-59 d to recent observations using a coupled atmosphere–interior evolutionary model. We find that the observations can be explained by in situ photochemical production of SO 2 in an H 2 background, indicative of a chemically reducing mantle and substantial (>1.8 mass%) early sulfur and hydrogen content, inconsistent with both the gas-dwarf and water-world scenarios. L 98-59 d’s interior comprises a permanent magma ocean, allowing long-term retention of volatiles within its mantle over billions of years, consistent with California-Kepler Survey trends. Our analysis reveals an evolutionary pathway in which planets host volatile-rich atmospheres sustained by long-term magma-ocean degassing, shaped by secular cooling, atmospheric erosion and photochemistry. Internal and environmental processes contribute to the observed diversity of super-Earth and sub-Neptune exoplanets.
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A Stratification-Dependent, Enstrophy-Controlled Regime in Baroclinic Turbulence Experiments in the Laboratory

(2026)

Authors:

Peter Read, Shanshan Ding, Hadrien Bobas, Hélène Scolan, Roland Young

Abstract:

The circulation of the Earth’s atmosphere and those of many other planets is dominated by turbulent interactions in a baroclinically unstable, rotating, stratified flow. Even for the Earth, which has been well observed for many years, the energy spectrum and complex properties of the anisotropic and inhomogeneous turbulent cascades of energy and enstrophy remain poorly understood and difficult to model accurately. Here we measure geostrophic turbulence energised by baroclinic instability in a rotating, differentially heated fluid annulus in the laboratory, which is bounded by convectively-driven warm and cold flows at the outer and inner boundaries, respectively (see Fig. 1a). Horizontal velocity fields (Fig. 1b-c) are obtained via particle image velocimetry of neutrally buoyant particles suspended in the flow, while the temperature structure is sampled using a vertical array of thermocouples located in the middle of the channel. The horizontal kinetic energy spectra exhibit a wavenumber range at relatively large length scales which scales as k−3, where k denotes the horizontal wavenumber (see Fig. 1d-e). Moreover, the spectral amplitude is found to correlate with the square of the Brunt–Vaisala frequency N at the same heights as the velocity measurements. The observed turbulent state exhibits a net forward enstrophy cascade across all scales, along with bidirectional kinetic energy transfer, which is indicated by a reversal in the sign of the spectral energy flux. The change of sign of the kinetic energy cascade occurs at a scale proportional to the internal Rossby radius of deformation Ld. These findings highlight the role of baroclinic instability in shaping the distribution of energy across scales with implications for synoptic- and meso-scale turbulent flows in the atmospheres of the Earth and other terrestrial planet atmospheres and oceans.FIG. 1. (a) Schematic plot of the convective tank. Snapshots of vorticity ζ for thermal Rossby number RoT = 5.41 (b) and RoT = 0.03 (c). On the scale bar, Lid = 2.4 cm and Liid = 22.6 cm are the Rossby radius of deformation for (c) and (b), respectively. (d) Kinetic energy spectra, E(k), for various values of RoT. The arrow indicates the wave number kp corresponding to the peak of E(k) when RoT = 0.03. Inset: radial profiles of temporal- and zonal-averaged azimuthal velocity, Uθ. (e) Kinetic energy spectra compensated by k−3 and normalised by N2 versus LRk. The dashed line indicates the plateau segment for LRk ∈ [2, 10] and has a magnitude of ∼ 0.5. Data are for height h = 0.18 m. 
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Emergence of Robust Zonal Jets in a Differentially Heated Rotating Annulus

(2026)

Authors:

Shanshan Ding, Peter Read

Abstract:

The midlatitude atmospheres of gas giant planets are characteristic of strong and persistent zonal jets; however, the processes governing their formation and the associated energy pathways remain less understood. To investigate these mechanisms, we conducted a laboratory study of zonal jets driven by thermal forcing in an annular cylindrical tank partially filled with distilled water as the working fluid. Heating is applied at the outer boundary, cooling at the inner boundary, the bottom is thermally insulated, and the top is a free surface. An array of laser diodes embedded in the inner cylinder generates an annular laser sheet, enabling the measurement of velocity fields at a fixed height using particle image velocimetry. By systematically varying the rotation rate and the imposed temperature contrast, we adjusted the steepness of the free surface, thus the topographic β effect, and the thermal forcing strength, respectively. The non-dimensional controlling parameter, thermal Rossby number, RoT, ranges from 0.0012 to 0.01 and Taylor number, Ta, from 2.3 × 1010 to1.7 × 1011. We discerned the emergence of robust zonal jets, of which the zonal-mean kinetic energy accounts for up to 70% of the total kinetic energy, corresponding to a zonostrophic index of 2.7. In this regime, two coherent and persistent prograde jets form near the inner and outer boundaries. The radial profile of the potential vorticity develops toward a pronounced staircase-like structure, consistent with previous numerical studies (Scott and Dritschel, J. Fluid Mech., 2012). Analysis of the inter-scale energy transfer reveals a dominant interaction between the zonal-mean flow and eddies, while the kinetic energy spectrum of the zonal-mean component exhibits k−5 (where k denotes the wavenumber), in agreement with the theory of zonostrophic turbulence (Sukoriansky and Galperin, PRL, 2002).                                     Figure 1: A snapshot of azimuthal velocity contour for RoT = 7.1 × 10−3, Ta = 1.44 × 1011 and β =49.7 m−1 s−1. 
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Novel Physics of Escaping Secondary Atmospheres May Shape the Cosmic Shoreline

2026 ApJ 998 236

Authors:

Richard D. Chatterjee, Raymond T. Pierrehumbert

Abstract:

Recent James Webb Space Telescope observations of cool, rocky exoplanets reveal a probable lack of thick atmospheres, suggesting prevalent escape of the secondary atmospheres formed after losing primordial hydrogen. Yet, simulations indicate that hydrodynamic escape of secondary atmospheres, composed of nitrogen and carbon dioxide, requires intense fluxes of ionizing radiation (XUV) to overcome the effects of high molecular weight and efficient line cooling. This transonic outflow of hot, ionized metals (not hydrogen) presents a novel astrophysical regime ripe for exploration. We introduce an analytic framework to determine which planets retain or lose their atmospheres, positioning them on either side of the cosmic shoreline. We model the radial structure of escaping atmospheres as polytropic expansions - power-law relationships between density and temperature driven by local XUV heating. Our approach diagnoses line cooling with a three-level atom model and incorporates how ion-electron interactions reduce mean molecular weight. Crucially, hydrodynamic escape onsets for a threshold XUV flux dependent upon the atmosphere's gravitational binding. Ensuing escape rates either scale linearly with XUV flux when weakly ionized (energy-limited) or are controlled by a collisional-radiative thermostat when strongly ionized. Thus, airlessness is determined by whether the XUV flux surpasses the critical threshold during the star's active periods, accounting for expendable primordial hydrogen and revival by volcanism. We explore atmospheric escape from Young-Sun Mars and Earth, LHS-1140 b and c, and TRAPPIST-1 b. Our modeling characterizes the bottleneck of atmospheric loss on the occurrence of observable Earth-like habitats and offers analytic tools for future studies.
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Diurnal Variability Modulates Episodic Convection in Hothouse Climates Over Ocean and Swamp‐Like Surface Conditions

Journal of Advances in Modeling Earth Systems American Geophysical Union (AGU) 18:2 (2026) e2025MS004992

Authors:

Namrah Habib, Guy Dagan, Nathan Steiger

Abstract:

Abstract Hot and moist “hothouse” climates occurred in Earth's past and are expected in Earth's far future climate, driven by increasing solar luminosity. In hothouse climate regimes, precipitation transitions from a quasi‐steady state, as in present‐day tropical convection, to an “episodic deluge” or relaxation‐oscillator (RO) regime where precipitation occurs in intense bursts separated by multi‐day dry spells. Recent studies suggest that the transition to RO convection regimes is radiatively driven. However, the transition from steady state to RO convection has only been studied with radiative convective equilibrium (RCE) simulations with constant insolation, excluding the diurnal cycle. Precipitation and convection are strongly linked to the diurnal cycle in Earth's present climate over both land and ocean. We explore the impact of the diurnal cycle on the transition from steady state to RO convection using two sets of small‐domain RCE simulations with ocean and swamp‐like surface boundary conditions. Our RCE simulations with ocean boundary conditions show convection transitions to an episodic deluge regime at 322 K and the diurnal cycle modulates precipitation to occur during late‐night or near dawn, when convective inhibition is the weakest. Our RCE simulations with swamp‐like boundary conditions, which allow for mean surface temperature variations, show that as RO states emerge, the diurnal cycle modulates precipitation to primarily occur during the late‐afternoon to about dusk; but as the mean SST increases, precipitation occurs during the late‐night to dawn. These results show that the diurnal cycle strongly influences the timing of convection and precipitation patterns in extreme climates.
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