An extended low-density atmosphere around the Jupiter-sized planet WASP-193 b

TL;DR

WASP-193b is a highly unusual, extremely low-density gas giant orbiting a bright star, offering a prime target for atmospheric characterization and insights into planetary formation and evolution.

Contribution

This study reports the discovery and detailed characterization of WASP-193b, an outlier gas giant with an unprecedentedly low density, highlighting its potential for atmospheric studies with JWST.

Findings

WASP-193b has a mass of 0.139 MJup and a radius of 1.464 RJup.

Its density is approximately 0.059 g/cm^3, much lower than typical gas giants.

The planet is an excellent target for transmission spectroscopy with JWST.

Abstract

Gas giants transiting bright nearby stars provide crucial insights into planetary system formation and evolution mechanisms. Most of these planets exhibit certain average characteristics, serving as benchmarks for our understanding of planetary systems. However, outliers like the planet we present in this study, WASP-193b, offer unique opportunities to explore unconventional formation and evolution processes. This planet completes an orbit around its Vmag=12.2 F9 main-sequence host star every 6.25 d. Our analyses found that WASP-193b has a mass of Mp=0.139+/-0.029 MJup and a radius of Rp=1.464+/-0.058 RJup, translating into an extremely low density of rho_p = 0.059+/-0.014 g/cm^3, at least one order of magnitude less than standard gas giants like Jupiter. Typical gas giants such as Jupiter have densities that range between 0.2 and 2 g/cm^3. The combination of its large transit depth (dF~1.4%), its extremely-low density, its high-equilibrium temperature (Teq = 1254+/-31 K), and the infrared brightness of its host star (magnitude Kmag=10.7) makes WASP-193b an exquisite target for characterization by transmission spectroscopy (transmission spectroscopy metric: TSM~600). One single JWST transit observation would yield detailed insights into its atmospheric properties and planetary mass, providing a unique window to explore the mechanisms behind its exceptionally low density and shed light on giant planets' diverse nature.