HD 20329b: An ultra-short-period planet around a solar-type star found by TESS

Abstract

Context. Ultra-short-period (USP) planets are defined as planets with orbital periods shorter than one day. This type of planets is rare, highly irradiated, and interesting because their formation history is unknown. Aims. We aim to obtain precise mass and radius measurements to confirm the planetary nature of a USP candidate found by the Transiting Exoplanet Survey Satellite (TESS). These parameters can provide insights into the bulk composition of the planet candidate and help to place constraints on its formation history. Methods. We used TESS light curves and HARPS-N spectrograph radial velocity measurements to establish the physical properties of the transiting exoplanet candidate found around the star HD 20329 (TOI-4524). We performed a joint fit of the light curves and radial velocity time series to measure the mass, radius, and orbital parameters of the candidate. Results. We confirm and characterize HD 20329b, a USP planet transiting a solar-type star. The host star (HD 20329, V = 8.74 mag, J = 7.5 mag) is characterized by its G5 spectral type with M = 0.90 ± 0.05 M , R = 1.13 ± 0.02 R , and T eff = 5596 ± 50 K; it is located at a distance d = 63.68 ± 0.29 pc. By jointly fitting the available TESS transit light curves and follow-up radial velocity measurements, we find an orbital period of 0.9261 ± (0.5 × 10 −4 ) days, a planetary radius of 1.72 ± 0.07 R ⊕ , and a mass of 7.42 ± 1.09 M ⊕ , implying a mean density of ρ p = 8.06 ± 1.53 g cm −3 . HD 20329b joins the ∼30 currently known USP planets with radius and Doppler mass measurements.

The TESS-Keck Survey. XII. A Dense 1.8 R ⊕ Ultra-short-period Planet Possibly Clinging to a High-mean-molecular-weight Atmosphere after the First Gigayear

“…With a core mass larger than 10 M ⊕ , TOI-1347 b, along with the USPs TOI-1075 b (Essack et al 2023) and HD 20329 b (Murgas et al 2022), are close to the theoretical limit for runaway accretion (see, e.g., Rafikov 2006). How did these planets evade runaway accretion and not become gas giants?…”

Lava planets interior dynamics govern the long-term evolution of their magma oceans

“…Astronomers have recently discovered a new class of exoplanets that offer a unique window into rocky interiors: lava planets [1][2][3][4][5][6][7][8]. These planets have densities consistent with Earth-like bulk composition but orbit so close to their star, that they are expected to have lost all their volatiles to space [9].…”