Gas giants transiting bright nearby stars provide crucial insights into planetary system formation and evolution mechanisms. Most of these planets show certain average characteristics, serving as benchmarks for our understanding of planetary systems. However, outliers like the planet we present in this study, WASP-193 b, offer unique opportunities to explore unconventional formation and evolution processes. This planet completes an orbit around its V-band-magnitude 12.2 F9 main-sequence host star every 6.25 days. Our analyses found that WASP-193 b has a mass of 0.139 ± 0.029 M_J and a radius of 1.464 ± 0.058 R_J, translating into an extremely low density of 0.059 ± 0.014g 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 g cm⁻³ and 2 g cm⁻³. The combination of its large transit depth (1.4%), extremely low density, high-equilibrium temperature (1,254 ± 31 K) and the infrared brightness of its host star (K-band magnitude 10.7) makes WASP-193 b an exquisite target for characterization by transmission spectroscopy (transmission spectroscopy metric ~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.

凌日附近明亮恒星的气态巨行星为行星系统的形成和演化机制提供了重要的见解。这些行星大多数都表现出某些平均特征，作为我们理解行星系统的基准。然而，像我们在这项研究中展示的行星 WASP-193 b 这样的异常值，为探索非常规形成和演化过程提供了独特的机会。这颗行星每 6.25 天绕其V波段星等 12.2 F9 主序主恒星运行一周。我们的分析发现，WASP-193 b 的质量为 0.139 ± 0.029  M _J，半径为 1.464 ± 0.058  R _J，换算成极低的密度为 0.059 ± 0.014g cm ^-3，至少比像木星这样的标准气态巨行星。典型的气态巨行星（如木星）的密度范围在 0.2 g cm ^-3和 2 g cm ^-3之间。其大凌星深度 (1.4%)、极低密度、高平衡温度 (1,254 ± 31 K) 及其主星的红外亮度（K波段星等 10.7）的结合使 WASP-193 b 成为观测的绝佳目标。通过透射光谱表征（透射光谱度量〜600）。一次 JWST 凌日观测将详细了解其大气特性和行星质量，提供一个独特的窗口来探索其极低密度背后的机制，并揭示巨行星的多样性性质。