A Pair of Dynamically Interacting Sub-Neptunes around TOI-6054
September 2025 • 2025AJ....170..150K
Abstract • We confirm the planetary nature of a pair of transiting sub-Neptune exoplanets orbiting the bright F-type subgiant star TOI-6054 (V = 8.02, K = 6.673) as a part of the OrCAS radial velocity survey using WIYN/NEID observations. We find that TOI-6054b and TOI-6054c have radii of 2.64 ± 0.15R⊕ and 2.82 ± 0.17R⊕, respectively, and masses of 12.5 ± 1.7M⊕ and 9.3 ± 1.9M⊕. The planets have zero-albedo equilibrium temperatures of 1360 ± 32 K and 1143 ± 28 K. The host star has expanded and will evolve off of the main sequence within the next ∼500 Myr, and the resulting increase in stellar luminosity has more than doubled the stellar flux the two planets receive compared to the start of the host star's main-sequence phase. Consequently, TOI-6054b may be losing some of its primordial hydrogen/helium atmosphere—if it has one. Based on dynamical simulations performed using the orbital parameters of the two planets, TOI-6054b, and TOI-6054c are very likely in a 5:3 mean motion resonance. The TOI-6054 system thus has the potential to be an excellent candidate for future atmospheric follow-up observations, with two similarly sized sub-Neptunes around a bright star. We also estimate that if TOI-6054b is currently losing its H/He atmosphere, this should be observable from space and from the ground.
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