The dynamics of Jupiter’s and Saturn’s weather layers: a synthesis after Cassini and Juno

Annual Review of Fluid Mechanics Annual Reviews 56 (2024)

Abstract:

Until recently, observations of the giant planets of our Solar System were confined to sampling relatively shallow regions of their atmospheres, leaving many uncertainties as to the dynamics of deeper layers. The Cassini and Juno missions to Saturn and Jupiter, however, have begun to address these issues, for example, by measuring their gravity and magnetic fields. The results show that the zonally coherent jets and cloud bands extend to levels where the electrical conductivity of the fluid becomes significant, whereas large-scale vortices, such as the Great Red Spot, are relatively shallow but may have deep-seated roots. The polar regions also exhibit intense cyclonic vortices that, on Jupiter, arrange themselves into remarkably regular “vortex crystals.” Numerical models seem able to capture some of this complexity, but many issues remain unresolved, suggesting a need for models that can represent both deep and shallow processes sufficiently realistically to compare with observations.

Near-Infrared Transmission Spectroscopy of HAT-P-18$\,$b with NIRISS: Disentangling Planetary and Stellar Features in the Era of JWST

ArXiv 2310.1495 (2023)

Authors:

Marylou Fournier-Tondreau, Ryan J MacDonald, Michael Radica, David Lafrenière, Luis Welbanks, Caroline Piaulet, Louis-Philippe Coulombe, Romain Allart, Kim Morel, Étienne Artigau, Loïc Albert, Olivia Lim, René Doyon, Björn Benneke, Jason F Rowe, Antoine Darveau-Bernier, Nicolas B Cowan, Nikole K Lewis, Neil James Cook, Laura Flagg, Frédéric Genest, Stefan Pelletier, Doug Johnstone, Lisa Dang, Lisa Kaltenegger, Jake Taylor, Jake D Turner

Atmospheric Reconnaissance of TRAPPIST-1 b with JWST/NIRISS: Evidence for Strong Stellar Contamination in the Transmission Spectra

The Astrophysical Journal Letters American Astronomical Society 955:1 (2023) l22

Authors:

Olivia Lim, Björn Benneke, René Doyon, Ryan J MacDonald, Caroline Piaulet, Étienne Artigau, Louis-Philippe Coulombe, Michael Radica, Alexandrine L’Heureux, Loïc Albert, Benjamin V Rackham, Julien de Wit, Salma Salhi, Pierre-Alexis Roy, Laura Flagg, Marylou Fournier-Tondreau, Jake Taylor, Neil J Cook, David Lafrenière, Nicolas B Cowan, Lisa Kaltenegger, Jason F Rowe, Néstor Espinoza, Lisa Dang, Antoine Darveau-Bernier

Equatorial waves and superrotation in the stratosphere of a Titan general circulation model

Planetary Science Journal IOP Publishing 4:8 (2023) 149

Authors:

Neil Lewis, Nicholas Lombardo, Peter Read, Juan Lora

Abstract:

We investigate the characteristics of equatorial waves associated with the maintenance of superrotation in the stratosphere of a Titan general circulation model. A variety of equatorial waves are present in the model atmosphere, including equatorial Kelvin waves, equatorial Rossby waves, and mixed Rossby–gravity waves. In the upper stratosphere, acceleration of superrotation is strongest around solstice and is due to interaction between equatorial Kelvin waves and Rossby-type waves in winter hemisphere midlatitudes. The existence of this "Rossby–Kelvin"-type wave appears to depend on strong meridional shear of the background zonal wind that occurs in the upper stratosphere at times away from the equinoxes. In the lower stratosphere, acceleration of superrotation occurs throughout the year and is partially induced by equatorial Rossby waves, which we speculate are generated by quasigeostrophic barotropic instability. Acceleration of superrotation is generally due to waves with phase speeds close to the zonal velocity of the mean flow. Consequently, they have short vertical wavelengths that are close to the model's vertical grid scale and therefore likely to be not properly represented. We suggest that this may be a common issue among Titan general circulation models that should be addressed by future model development.

A mineralogical reason why all exoplanets cannot be equally oxidising

Monthly notices of the Royal Astronomical Society (2023) stad2486

Authors:

Claire Marie Guimond, Oliver Shorttle, Sean Jordan, John F Rudge

Abstract:

From core to atmosphere, the oxidation states of elements in a planet shape its character. Oxygen fugacity (⁠fO2⁠) is one parameter indicating these likely oxidation states. The ongoing search for atmospheres on rocky exoplanets benefits from understanding the plausible variety of their compositions, which depends strongly on their oxidation states—and if derived from interior outgassing, on the fO2 at the top of their silicate mantles. This fO2 must vary across compositionally-diverse exoplanets, but for a given planet its value is unconstrained insofar as it depends on how iron (the dominant multivalent element) is partitioned between its 2+ and 3+ oxidation states. Here we focus on another factor influencing how oxidising a mantle is—a factor modulating fO2 even at fixed Fe3+/Fe2+—the planet’s mineralogy. Only certain minerals (e.g., pyroxenes) incorporate Fe3+. Having such minerals in smaller mantle proportions concentrates Fe3+, increasing fO2⁠. Mineral proportions change within planets according to pressure, and between planets according to bulk composition. Constrained by observed host star refractory abundances, we calculate a minimum fO2 variability across exoplanet mantles, of at least two orders of magnitude, due to mineralogy alone. This variability is enough to alter by a hundredfold the mixing ratio of SO2 directly outgassed from these mantles. We further predict that planets orbiting high-Mg/Si stars are more likely to outgas detectable amounts of SO2 and H2O; and for low-Mg/Si stars, detectable CH4, all else equal. Even absent predictions of Fe3+ budgets, general insights can be obtained into how oxidising an exoplanet’s mantle is.