Company for the ultra-high density, ultra-short period sub-Earth GJ 367 b: discovery of two additional low-mass planets at 11.5 and 34 days

Abstract

GJ 367 is a bright (V $\approx$ 10.2) M1 V star that has been recently found to host a transiting ultra-short period sub-Earth on a 7.7 hr orbit. With the aim of improving the planetary mass and radius and unveiling the inner architecture of the system, we performed an intensive radial velocity follow-up campaign with the HARPS spectrograph -- collecting 371 high-precision measurements over a baseline of nearly 3 years -- and combined our Doppler measurements with new TESS observations from sectors 35 and 36. We found that GJ 367 b has a mass of $M_{\mathrm{b}}$ = 0.633 $\pm$ 0.050 M${}_{\oplus }$ and a radius of $R_{\mathrm{b}}$ = 0.699 $\pm$ 0.024 R${}_{\oplus }$, corresponding to precisions of 8% and 3.4%, respectively. This implies a planetary bulk density of ${\rho }_{\mathrm{b}}$ = 10.2 $\pm$ 1.3 g cm${}^{-3}$, i.e., 85% higher than Earth's density. We revealed the presence of two additional non transiting low-mass companions with orbital periods of $\sim$11.5 and 34 days and minimum masses of $M_{\mathrm{c}}\sin i_{\mathrm{c}}$ = 4.13 $\pm$ 0.36 M${}_{\oplus }$ and $M_{\mathrm{d}}\sin i_{\mathrm{d}}$ = 6.03 $\pm$ 0.49 M${}_{\oplus }$, respectively, which lie close to the 3:1 mean motion commensurability. GJ 367 b joins the small class of high-density planets, namely the class of super-Mercuries, being the densest ultra-short period small planet known to date. Thanks to our precise mass and radius estimates, we explored the potential internal composition and structure of GJ 367 b, and found that it is expected to have an iron core with a mass fraction of 0.91${}_{-0.23}^{+0.07}$. How this iron core is formed and how such a high density is reached is still not clear, and we discuss the possible pathways of formation of such a small ultra-dense planet.

arXiv comment28 pages, 11 figures. Accepted for publication in ApJL

References in corpus (83)

• Analytic Lightcurves for Planetary Transit Searches
• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• Kepler Presearch Data Conditioning II - A Bayesian Approach to Systematic Error Correction
• The Revised TESS Input Catalog and Candidate Target List
• The Occurrence and Architecture of Exoplanetary Systems
• Kepler Presearch Data Conditioning I - Architecture and Algorithms for Error Correction in Kepler Light Curves
• How to Constrain Your M Dwarf: measuring effective temperature, bolometric luminosity, mass, and radius
• The TESS Input Catalog and Candidate Target List
• Understanding the Mass-Radius Relation for Sub-Neptunes: Radius as a Proxy for Composition
• Homogeneous studies of transiting extrasolar planets. IV. Thirty systems with space-based light curves
• Masses, Radii, and Orbits of Small Kepler Planets: The Transition from Gaseous to Rocky Planets
• Spectrum radial velocity analyser (SERVAL). High-precision radial velocities and two alternative spectral indicators
• Large-scale magnetic topologies of mid-M dwarfs
• Mass-Radius Relation for Rocky Planets based on PREM
• Collisions Between Gravity-Dominated Bodies: 1. Outcome Regimes and Scaling Laws
• Collisions between Gravity-Dominated Bodies: 2. The Diversity of Impact Outcomes during the End Stage of Planet Formation
• A Gaussian process framework for modelling stellar activity signals in radial velocity data
• Least squares deconvolution of the stellar intensity and polarization spectra
• How to Constrain Your M dwarf II: the mass-luminosity-metallicity relation from 0.075 to 0.70$M_{\odot }$
• The Updated BaSTI Stellar Evolution Models and Isochrones: I. Solar Scaled Calculations
• On the age of the $\beta$ Pictoris moving group
• Gaia Early Data Release 3: The Gaia Catalogue of Nearby Stars
• Large-scale magnetic topologies of early M dwarfs
• Limb and gravity-darkening coefficients for the TESS satellite at several metallicities, surface gravities, and microturbulent velocities
• A new list of thorium and argon spectral lines in the visible
• Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library
• The inner regions of protoplanetary disks
• A Study of the Shortest-Period Planets Found With Kepler
• Revisited Mass-Radius relations for exoplanets below 120 Earth masses
• A lithium depletion boundary age of 21 Myr for the Beta Pictoris moving group
• A generalized bayesian inference method for constraining the interiors of super Earths and sub-Neptunes
• Six transiting planets and a chain of Laplace resonances in TOI-178
• Magnetic activity in the HARPS M-dwarf sample. The rotation-activity relationship for very low-mass stars through R'HK
• Angular Momentum Loss from Cool Stars: An Empirical Expression and Connection to Stellar Activity
• Testing the recovery of stellar rotation signals from Kepler light curves using a blind hare-and-hounds exercise
• Chromospheric activity as age indicator
• CARMENES input catalogue of M dwarfs V. Luminosities, colours, and spectral energy distributions
• Minimum Radii of Super-Earths: Constraints from Giant Impacts
• The HARPS search for southern extra-solar planets XLI. A dozen planets around the M dwarfs GJ 3138, GJ 3323, GJ 273, GJ 628, and GJ 3293
• On the Mass of CoRoT-7b
• Transiting extrasolar planetary candidates in the Galactic bulge
• From stellar nebula to planets: the refractory components
• WASP-30b: a 61 Mjup brown dwarf transiting a V=12, F8 star
• Magnetic fields of M dwarfs
• Magnetospheric Truncation, Tidal Inspiral, and the Creation of Short and Ultra-Short Period Planets
• Collisional Stripping and Disruption of Super-Earths
• Elemental ratios in stars vs planets
• Kepler-78 and the Ultra-Short-Period Planets
• A giant impact as the likely origin of different twins in the Kepler-107 exoplanet system
• An Investigation into the Radial Velocity Variations of CoRoT-7
• An Earth-sized exoplanet with a Mercury-like composition
• Pyaneti: a fast and powerful software suite for multi-planet radial velocity and transit fitting
• pyaneti II: A multidimensional Gaussian process approach to analysing spectroscopic time-series
• From planetesimals to planets: volatile molecules
• Exoplanets around Low-mass Stars Unveiled by K2
• Ultra-short-period planets from secular chaos
• Low-Eccentricity Migration of Ultra-Short Period Planets in Multi-Planet Systems
• The transiting multi-planet system HD3167: a 5.7 MEarth Super-Earth and a 8.3 MEarth mini-Neptune
• GJ 367b: A dense ultra-short period sub-Earth planet transiting a nearby red dwarf star
• Larger mutual inclinations for the shortest-period planets
• Formation of Ultra-Short-Period Planets by Obliquity-Driven Tidal Runaway
• K2-141 b: A 5-M${}_{\oplus }$ super-Earth transiting a K7 V star every 6.7 hours
• One year of AU Mic with HARPS: II -- stellar activity and star-planet interaction
• A Population of Very-Hot Super-Earths in Multiple-Planet Systems Should be Uncovered by Kepler
• The BAyesian STellar Algorithm (BASTA): a fitting tool for stellar studies, asteroseismology, exoplanets, and Galactic archaeology
• K2-106, a system containing a metal-rich planet and a planet of lower density
• Calibration of the Halpha Age-Activity relation for M dwarfs
• A study of the performance of the transit detection tool DST in space-based surveys. Application of the CoRoT pipeline to Kepler data
• A Compact Multi-Planet System With A Significantly Misaligned Ultra Short Period Planet
• One year of AU Mic with HARPS: I -- measuring the masses of the two transiting planets
• Rocklines as Cradles for Refractory Solids in the Protosolar Nebula
• TKS X: Confirmation of TOI-1444b and a Comparative Analysis of the Ultra-short-period Planets with Hot Neptunes
• HD 23472: A multi-planetary system with three super-Earths and two potential super-Mercuries
• Characterization of the K2-38 planetary system. Unraveling one of the densest planets known to date
• Three-dimensional magnetic and abundance mapping of the cool Ap star HD 24712 I. Spectropolarimetric observations in all four Stokes parameters
• The TIME Table: Rotation and Ages of Cool Exoplanet Host Stars
• Magnetic Field of the Active Planet-hosting M Dwarf AU Mic
• Forming Iron-rich Planets with Giant Impacts
• Ultra Short Period Planets in K2 with companions: a double transiting system for EPIC 220674823
• A low-eccentricity migration pathway for a 13-h-period Earth analogue in a four-planet system
• The HD 137496 system: A dense, hot super-Mercury and a cold Jupiter
• The Gaia-ESO survey: A lithium depletion boundary age for NGC 2232
• High-contrast, high-angular resolution view of the GJ 367 exoplanet system

Cited by in corpus (15)

• From super-Earths to sub-Neptunes: Observational constraints and connections to theoretical models
• GJ 367b is a dark, hot, airless sub-Earth
• WIde Separation Planets In Time (WISPIT): A Gap-clearing Planet in a Multi-ringed Disk around the Young Solar-type Star WISPIT 2
• Unveiling the internal structure and formation history of the three planets transiting HIP 29442 (TOI-469) with CHEOPS
• Population-level Hypothesis Testing with Rocky Planet Emission Data: A Tentative Trend in the Brightness Temperatures of M-Earths
• Constraining exoplanet interiors using observations of their atmospheres
• Characterizing WASP-43b's interior structure: unveiling tidal decay and apsidal motion
• Validation of a Third Planet in the LHS 1678 System
• The high-energy environment of the heavy sub-Earth GJ 367 b indicates likely complete evaporation of its atmosphere
• Two neighbours of the ultra-short-period Earth-sized planet K2-157 b in the warm Neptunian savanna
• Homogeneous planet masses I: Reanalysis of archival HARPS radial velocities
• Partial disruption of a planet around a white dwarf: the effect of perturbation from the remnant planet on the accretion
• No Robust Statistical Evidence for a Population of Water Worlds in a 2025 Sample of Planets Orbiting M Stars
• A Validated Low-to-Intermediate Mass Planetary Interior Structure Model and New Mass-Radius Relations
• The role of inner disk edges in shaping ultra-short-period planet systems around late M dwarfs