Revisiting the warm sub-Saturn TOI-1710b. The impact of stellar activity on the mass measurement

The Transiting Exoplanet Survey Satellite (TESS) provides a continuous suite of new planet candidates that need confirmation and precise mass determination from ground-based observatories. This is the case for the G-type star TOI-1710, which is known to host a transiting sub-Saturn planet (M_p = 28.3 ± 4.7 M_⊕) in a long-period orbit (P = 24.28 days). Here we combine archival SOPHIE and new and archival HARPS-N radial velocity data with newly available TESS data to refine the planetary parameters of the system and derive a new mass measurement for the transiting planet, taking into account the impact of the stellar activity on the mass measurement. We report for TOI-1710b a radius of R_p = 5.15 ± 0.12 R_⊕, a mass of M_p = 18.4 ± 4.5 M_⊕, and a mean bulk density of ρ_p = 0.73 ± 0.18 g cm⁻³, which are consistent at 1.2σ, 1.5σ, and 0.7σ, respectively, with previous measurements. Although there is not a significant difference in the final mass measurement, we needed to add a Gaussian process component to successfully fit the radial velocity dataset. This work illustrates that adding more measurements does not necessarily imply a better mass determination in terms of precision, even though they contribute to increasing our full understanding of the system. Furthermore, TOI-1710b joins an intriguing class of planets with radii in the range 4-8 R_⊕ that have no counterparts in the Solar System. A large gaseous envelope and a bright host star make TOI-1710b a very suitable candidate for follow-up atmospheric characterization.