Water/Hycean Worlds & Oceanography

TOI-544 b: A Potential Water-world Inside The Radius Valley In A Two-planet System

By Keith Cowing

Status Report

astro-ph.EP

October 24, 2023

Filed under astro-ph.EP, atmosphere, Earth-like Planet, exoplanet, HARPS, HARPS-N, HD 290498, JWST, K star, rocky planet, Spectroscopy, TESS, TOI-544, TOI-544b, TOI-544c

TOI-544 b: A Potential Water-world Inside The Radius Valley In A Two-planet System — Mass-radius diagram showing confirmed planets with mass uncertainties < 20% in grey circles, with TOI-544 b shown as the black circle. Left: the coloured tracks show different potential planet compositions from Zeng et al. (2019), assuming a planetary equilibrium temperature of 1000 K. The dashed lines show compositions of an Earth-like rocky core surrounded by a layer of H-He in varying percentages by mass, the solid lines show water world compositions with varying water mass fractions, the dotted lines show rocky and Earth-like rocky compositions. TOI-544 b is closest to the tracks with 100% H2O and 50% H2O with 50% rock. Right: the same as the left panel but the the dashed lines show compositions of an Earth-like rocky core surrounded by a layer of H-He in varying percentages by mass from Lopez & Fortney (2014) using the models for a 10Gyr planet, with solar metalicity and flux of 10F⊕, the solid lines show compositions from Aguichine et al. (2021) of irradiated ocean worlds with varying water mass fractions, and the dotted lines show the same rocky and Earth-like rocky compositions from Zeng et al. (2019). TOI-544 b is closest to models with either 30% water mass fraction, or a rocky core with a Hydrogen envelope of between 0.5 - 1%. The data is downloaded from the NASA Exoplanet Archive. -- astro-ph.EP

We report on the precise radial velocity follow-up of TOI-544 (HD 290498), a bright K star (V=10.8), which hosts a small transiting planet recently discovered by the Transiting Exoplanet Survey Satellite (TESS). We collected 122 high-resolution HARPS and HARPS-N spectra to spectroscopically confirm the transiting planet and measure its mass.

The nearly 3-year baseline of our follow-up allowed us to unveil the presence of an additional, non-transiting, longer-period companion planet. We derived a radius and mass for the inner planet, TOI-544b, of 2.018 ± 0.076 R⊕ and 2.89 ± 0.48 M⊕ respectively, which gives a bulk density of 1.93+0.30−0.25 g cm−3.

TOI-544c has a minimum mass of 21.5 ± 2.0 M⊕ and orbital period of 50.1 ± 0.2 days. The low density of planet-b implies that it has either an Earth-like rocky core with a hydrogen atmosphere, or a composition which harbours a significant fraction of water. The composition interpretation is degenerate depending on the specific choice of planet interior models used.

Additionally, TOI-544b has an orbital period of 1.55 days and equilibrium temperature of 999 ± 14 K, placing it within the predicted location of the radius valley, where few planets are expected. TOI-544b is a top target for future atmospheric observations, for example with JWST, which would enable better constraints of the planet composition.

H. L. M. Osborne, V. Van Eylen, E. Goffo, D. Gandolfi, G. Nowak, C. M. Persson, J. Livingston, A. Weeks, E. Pallé, R. Luque, C. Hellier, I. Carleo, S. Redfield, T. Hirano, M. Garbaccio Gili, J. Alarcon, O. Barragán, N. Casasayas-Barris, M. R. Díaz, M. Esposito, J. S. Jenkins, E. Knudstrup, F. Murgas, J. Orell-Miquel, F. Rodler, L. Serrano, M. Stangret, S. H. Albrecht, A. Alqasim, W. D. Cochran, H. J. Deeg, M. Fridlund, A. Hatzes, J. Korth, K. W. F. Lam

Comments: Re-submitted to MNRAS following moderate review, 23 October 2023
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2310.14908 [astro-ph.EP] (or arXiv:2310.14908v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2310.14908
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Submission history
From: Hannah Osborne
[v1] Mon, 23 Oct 2023 13:17:50 UTC (3,757 KB)
https://arxiv.org/abs/2310.14908
Astrobiology

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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