Kavli Affiliate: Andrew M. Vanderburg
| First 5 Authors: Rachel B Fernandes, Shubham Kanodia, Megan Delamer, Andrew Hotnisky, Te Han
| Summary:
We present the confirmation of TOI-5573b, a Saturn-sized exoplanet on an
8.79-day orbit around an early M-dwarf (3790 K, 0.59 R$odot$, 0.61 M$odot$,
12.30 J mag). TOI-5573b has a mass of $112^{+18}_{-19}$ M$oplus$
(0.35$pm$0.06 M$mathrm{Jup}$) and a radius of $9.75pm0.47$ R$oplus$
(0.87$pm$0.04 R$mathrm{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
5$sigma$ 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 $528pm10$ 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.
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