Searching for GEMS: Confirmation of TOI-5573b, a Cool, Saturn-like Planet Orbiting An M-dwarf

We present the confirmation of TOI-5573 b, a Saturn-sized exoplanet on an 8.79-day orbit around an early M-dwarf (3790 K, 0.59 R_⊙, 0.61 M_⊙, 12.30 J mag). TOI-5573 b has a mass of 112+18−19 M_⊕ (0.35±0.06 M_Jup) and a radius of 9.75±0.47 R_⊕ (0.87±0.04 R_Jup), resulting in a density of 0.66+0.16−0.13 g cm⁻³, akin to that of Saturn.

The planet was initially discovered by TESS and confirmed using a combination of 11 transits from four TESS sectors (20, 21, 47 and 74), ground-based photometry from the Red Buttes Observatory, and high-precision radial velocity data from the Habitable-zone Planet Finder (HPF) and NEID spectrographs, achieving a 5σ precision on the planet’s mass.

TOI-5573b is one of the coolest Saturn-like exoplanets discovered around an M-dwarf, with an equilibrium temperature of 528±10 K, making it a valuable target for atmospheric characterization.

Saturn-like exoplanets around M-dwarfs likely form through core accretion, with increased disk opacity slowing gas accretion and limiting their mass. The host star’s super-solar metallicity supports core accretion, but uncertainties in M-dwarf metallicity estimates complicate definitive conclusions.

Compared to other GEMS (Giant Exoplanets around M-dwarf Stars) orbiting metal-rich stars, TOI-5573b aligns with the observed pattern that giant planets preferentially form around M-dwarfs with super-solar metallicity. Further high-resolution spectroscopic observations are needed to explore the role of stellar metallicity in shaping the formation and properties of giant exoplanets like TOI-5573b.

Rachel B Fernandes, Shubham Kanodia, Megan Delamer, Andrew Hotnisky, Te Han, Caleb I Canas, Jessica Libby-Roberts, Varghese Reji, Arvind F Gupta, Jaime A Alvarado-Montes, Chad F Bender, Cullen H Blake, William D Cochran, Zoe L de Beurs, Scott A Diddams, Jiayin Dong, Mark E Everett, Eric B Ford, Samuel Halverson, Jesus Higuera, Henry A Kobulnicky, Daniel M Krolikowski, Alexander Larsen, Andrea SJ Lin, Suvrath Mahadevan, Michael W McElwain, Andrew Monson, Joe P Ninan, Leonardo A Paredes, Yatrik G Patel, Paul Robertson, Gabrielle Ross, Arpita Roy, Christian Schwab, Gudmundur Stefansson, Daniel J Stevens, Andrew M Vanderburg, Jason Wright

Comments: 16 pages, 8 figures, 3 tables; accepted for publication to AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2505.08947 [astro-ph.EP] (or arXiv:2505.08947v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2505.08947
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Submission history
From: Rachel Fernandes
[v1] Tue, 13 May 2025 20:20:40 UTC (3,377 KB)
https://arxiv.org/abs/2505.08947
Astrobiology,