Cloud Formation and Dynamics in Cool Dwarf and Hot Exoplanetary Atmospheres

TL;DR

This review discusses the observational evidence, challenges, and modeling of cloud formation and atmospheric dynamics in cool dwarf stars, brown dwarfs, and hot exoplanets, highlighting their complexity and importance for understanding these objects.

Contribution

It provides a comprehensive summary of current observational findings, theoretical challenges, and the role of 3D models in studying clouds and dynamics in low-temperature atmospheres.

Findings

Cloud formation varies rapidly in brown dwarfs.

Exoplanets exhibit asymmetric, time-variable atmospheres.

Clouds influence thermal energy balance through albedo effects.

Abstract

The lowest-mass stars, brown dwarfs and extrasolar planets present challenges and opportunities for understanding dynamics and cloud formation processes in low-temperature atmospheres. For brown dwarfs, the formation, variation and rapid depletion of photospheric clouds in L- and T-type dwarfs, and spectroscopic evidence for non-equilibrium chemistry associated with vertical mixing, all point to a fundamental role for dynamics in vertical abundance distributions and cloud/grain formation cycles. For exoplanets, azimuthal heat variations and the detection of stratospheric and exospheric layers indicate multi-layered, asymmetric atmospheres that may also be time-variable (particularly for systems with highly elliptical orbits). Dust and clouds may also play an important role in the thermal energy balance of exoplanets through albedo effects. For all of these cases, 3D atmosphere models are becoming an increasingly essential tool for understanding spectral and temporal properties. In this review, I summarize the observational evidence for clouds and dynamics in cool dwarf and hot exoplanetary atmospheres, outstanding problems associated with these processes, and areas where effective synergy can be achieved.