Large-amplitude Variability Driven by Giant Dust Storms on a Planetary-mass Companion

TL;DR

This paper reveals that giant dust storms driven by planetary-scale weather patterns cause large-amplitude variability in a planetary-mass companion, challenging existing models of substellar atmospheres.

Contribution

It introduces a general circulation model showing that dust storms and patchy clouds explain observed variability and spectral features in VHS 1256B, a highly variable exoplanet-mass object.

Findings

Dust storms persist for tens of days

Large patchy clouds propagate with equatorial waves

Explains irregular light curve evolution and spectral features

Abstract

Large-amplitude variations are commonly observed in the atmospheres of directly imaged exoplanets and brown dwarfs. VHS 1256B, the most variable known planet-mass object, exhibits a near-infrared flux change of nearly 40%, with red color and silicate features revealed in recent JWST spectra, challenging current theories. Using a general circulation model, we demonstrate that VHS 1256B's atmosphere is dominated by planetary-scale dust storms persisting for tens of days, with large patchy clouds propagating with equatorial waves. This weather pattern, distinct from the banded structures seen on solar system giants, simultaneously explains the observed spectra and critical features in the rotational light curves, including the large amplitude, irregular evolution, and wavelength dependence, as well as the variability trends observed in near-infrared color-magnitude diagrams of dusty substellar atmospheres.