TOI-4552 b: A new ultra-short period rocky world revealed by NIRPS and TESS

TL;DR

This paper reports the discovery and detailed characterization of TOI-4552b, an ultra-short period Earth-sized rocky exoplanet orbiting an M dwarf, using TESS, ground-based photometry, speckle imaging, and spectroscopic data.

Contribution

The study confirms TOI-4552b as a new ultra-short period rocky planet and provides its mass, radius, and interior composition estimates, highlighting its potential for atmospheric studies.

Findings

TOI-4552b has a mass of 1.83±0.47 M⊕ and radius of 1.11±0.04 R⊕.

The planet's density suggests a possibly iron-rich interior, with a core mass fraction around 0.54.

TOI-4552b is a promising target for JWST atmospheric and surface composition observations.

Abstract

A particularly intriguing subclass of rocky exoplanets are the ultra-short period (USP) worlds that orbit their host stars in less than a day. These planets are particularly rare around M dwarf stars, with so far only ten that have a constrained mass and radius. We present the validation and characterization of the ultra-short period (0.3-days), Earth-sized planet TOI-4552b orbiting a nearby (27.26-pc away) M4.5V dwarf. Complementing the TESS photometry, ground-based transit observations from LCO, ExTrA and SPECULOOS validated the planetary radius and cleared the field of any contaminants. Speckle imaging with Zorro (Gemini-S) rules out false positive scenarios caused by eclipsing binary sources. Spectroscopic observations with NIRPS and HARPS were used to obtain stellar abundances, constrain the planetary mass, and, in conjunction with the transit observations, estimate the orbital parameters. TOI-4552 is a quiet star exhibiting no short-term stellar variations seen in photometric or radial velocity data that can be associated to stellar rotation. TOI-4552b ($M_p=1.83\pm0.47\,M_e$, $R_p=1.11\pm0.04\,R_e$) lies between the Earth-like and iron-rich composition tracks on the Mass-Radius diagram. The EXOPIE interior structure model, without constraints from refractory abundance ratio, yields a core mass fraction (CMF) of 0.54 and a bulk density of 7.74g/cm$^3$. Since the CMF spans a wide range due to the large uncertainty on the mass, the definitive interior composition cannot be determined with the current dataset. TOI-4552b hints as being marginally more iron-rich compared to the Earth but confirmation of its status requires additional, precise radial velocity measurements. Combined with its high emission spectroscopic metric (ESM=19.5), negligible stellar activity and short orbital period, TOI-4552b emerges as a compelling target for atmospheric and surface composition studies with JWST.