Synthetic atmospheric transmission spectra of Ross 176 b. Left: Fiducial models for clear or hazy H/He atmospheres with scaled solar abundances. Right: Model for a steam H2O atmosphere. Simulated measurements with error bars are shown for the observation of one (left) or ten (right) transits with JWST NIRISS-SOSS, NIRSpec-G395H, and MIRI-LRS configurations. — astro-ph.EP
The case of Ross 176 is a late K-type star that hosts a promising water-world candidate planet. The star has a radius of R∗=0.569±0.020R⊙ and a mass of M⋆ = 0.577 ± 0.024 M⊙.
We constrained the planetary mass using spectroscopic data from CARMENES, an instrument that has already played a major role in confirming the planetary nature of the transit signal detected by TESS.
We used Gaussian Processes (GP) to improve the analysis because the host star has a relatively strong activity that affects the radial velocity dataset. In addition, we applied a GP to the TESS light curves to reduce the correlated noise in the detrended dataset. The stellar activity indicators show a strong signal that is related to the stellar rotation period of ∼ 32 days.
This stellar activity signal was also confirmed on the TESS light curves. Ross 176b is an inner hot transiting planet with a low-eccentricity orbit of e=0.25±0.04, an orbital period of P∼5 days, and an equilibrium temperature of Teq∼682K.
With a radius of Rp=1.84±0.08R⊕ (4% precision), a mass of Mp=4.57+0.89−0.93M⊕ (20% precision), and a mean density of ρp=4.03+0.49−0.81gcm−3, the composition of Ross 176b might be consistent with a water-world scenario. Moreover, Ross 176b is a promising target for atmospheric characterization, which might lead to more information on the existence, formation and composition of water worlds.
This detection increases the sample of planets orbiting K-type stars. This sample is valuable for investigating the valley of planets with small radii around this type of star. This study also shows that the dual detection of space- and ground-based telescopes is efficient for confirm new planets.
S. Geraldía-González, J. Orell-Miquel, E. Pallé, F. Murgas, G. Lacedelli, V. J. S. Béjar, J. A. Caballero, C. Duque-Arribas, J. Lillo-Box, D. Montes, G. Morello, E. Nagel, A. Schweitzer, H. M. Tabernero, Y. Calatayud-Borras, C. Cifuentes, G. Fernández-Rodríguez, A. Fukui, J. de Leon, N. Lodieu, R. Luque, M. Mori, N. Narita, H. Parviainen, E. Poultourtzidis, A. Reiners, I. Ribas, M. Schlecker, S. Seager, K. G. Stassun, T. Trifonov, S. Vanaverbeke, J. N. Winn
Comments: Accepted for publication in A&A. 16 pages. 13 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2507.15763 [astro-ph.EP] (or arXiv:2507.15763v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2507.15763
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Related DOI:
https://doi.org/10.1051/0004-6361/202553719
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Submission history
From: Samuel Geraldía González
[v1] Mon, 21 Jul 2025 16:20:12 UTC (2,559 KB)
https://arxiv.org/abs/2507.15763
Astrobiology,