A low-eccentricity migration pathway for a 13-h-period Earth analogue in a four-planet system

Abstract

OI-500 (also known as HIP 34269, TIC 134200185 and CD-47 2804) is a high-proper-motion star (Table 1) with a radial velocity of 55.6 km s −1 (ref. 1 ) and a V-band magnitude of 10. 54 (ref. 2 ) located at a distance of 47.39 pc from the Sun 1 . The National Aeronautics and Space Administration's (NASA's) Transiting Exoplanet Survey Satellite 3 (TESS) observed TOI-500 for the first time in sectors 6, 7 and 8 between 11 December 2018 and 28 February 2019. The TESS Science Processing Operations Center 4 (SPOC) identified the signature of a possible Earth-sized transiting planet with an orbital period of nearly 13 hours. The candidate was subsequently designated as TOI-500.01 by the TESS Science Office and announced on 8 March 2019. We performed an independent analysis of the TESS light curves with the codes Détection Spécialisée de Transits 5 and Transit Least Square 6 , which confirmed the presence of the candidate (Fig. 1) and excluded additional significant transit signals. We used the Las Cumbres Observatory Global Telescope 7 (LCOGT) to perform photometric observations of the 78 neighbouring stars up to about Δmag ≈ 10 at angular separation between 12″ and 2.5′ from TOI-500 (Extended Data Fig. 1). The analysis of the retrieved light curves allowed us to exclude that those sources are contaminating eclipsing binaries mimicking the transit signal detected in the TESS light curves. Speckle images acquired with the 4.1 m Southern Astrophysical Research (SOAR) telescope (Cerro Tololo Inter-American Observatory, Chile) and the 8.1 m Gemini South telescope (Cerro Pachón, Chile) excluded the presence of nearby stars up to about Δmag ≈ 7, as close as 0.02″ (Zorro@Gemini speckle inner working angle; Extended Data Fig. 2) and out to 3″ (SOAR outer limit; Extended Data Fig. 3). Finally, we confirmed the planetary nature of the transit signal with an intensive radial velocity (RV) follow-up campaign carried out with the High-Accuracy Radial Velocity Planet Searcher 8 (HARPS) spectrograph mounted at the 3.6 m telescope of the European Southern Observatory (ESO, La Silla, Chile). We collected nearly 200 HARPS spectra of TOI-500 between 22 March 2019 and 23 March 2020. Our RV measurements also unveiled the presence of three additional Doppler signals that have no counterpart in any of the stellar activity indicators, providing strong evidence that they are induced by three additional planets . TOI-500 is thus orbited by (at least) four planets, three of which are not seen to transit their host star. To determine the planetary parameters, we

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*

“…In these models, planet migration occurs after the dissipation of the protoplanetary disk, by a combination of eccentricity forcing from the planetary companions and tidal dissipation in the innermost planet's interior, although the precise dynamical forcing mechanisms are debated. Serrano et al (2022) showed, for TOI-500, that the low-eccentricity secular forcing proposed by Pu & Lai (2019) can explain the migration of that system's USP planet from a formation radius of ∼0.02 au to its observed location. For GJ 367 b, we tested this migration scenario with similar initial conditions (USP planet starting at 0.02 au, initial eccentricities of all planets set to 0.2), and found only modest migration of planet b, from 0.02 au to ∼0.01 au, short of the observed 0.007 au.…”

“…The formation process of USP planets is still not fully understood, and different scenarios have been proposed to explain their short-period orbits: dynamical interactions in multiplanet systems (Schlaufman et al 2010); low-eccentricity migration due to secular planet-planet interactions (Pu & Lai 2019); high-eccentricity migration due to secular dynamical chaos (Petrovich et al 2019); tidal orbital decay of USP planets formed in situ (Lee & Chiang 2017); and obliquity-driven tidal migration (Millholland & Spalding 2020). Intensive follow-up observations of systems hosting USP planets can help us to understand the formation and evolution mechanisms of shortperiod objects and other phenomena related to star-planet interactions (Serrano et al 2022). Sanchis-Ojeda et al (2014), Adams et al (2017), andWinn et al (2018) found that most USP planets have nearby planetary companions.…”

TOI-1075 b: A Dense, Massive, Ultra-short-period Hot Super-Earth Straddling the Radius Gap

“…The presence of a second planet candidate motivates us to collect additional RV data for this system in order to determine the period and measure the mass of the second planet candidate while also improving the uncertainty on the mass measurement of TOI-1075 b. Additionally, there are currently a handful of systems consisting of a USP planet and a close-in companion with periods ranging from a few days to tens of days, e.g., K2-106 (Guenther et al 2017), K2-141 (Malavolta et al 2018), K2-229 (Santerne et al 2018, and TOI-500 (Serrano et al 2022). These close-in companions could be responsible for migrating the USP planets to their current positions (Pu & Lai 2019;Millholland & Spalding 2020;Serrano et al 2022). The possible existence of such a close-in companion in the TOI-1075 system serves as additional motivation for further RV follow-up of the system.…”

Fizzy Super-Earths: Impacts of Magma Composition on the Bulk Density and Structure of Lava Worlds

“…Within our planet sample, TOI-561 b, CoRoT-7 b, and TOI-500 b have the lowest bulk densities with densities of 3.00 ± 0.80 g cm −3 , 5 ± 1.5 g cm −3 , and -+ -4.9 g cm 0.88 1.03 3 , respectively (Léger et al 2011;Lacedelli et al 2021;Serrano et al 2022). However, we find that the lowest bulk density produced by our models for the same planet mass is only consistent with the measurements for TOI-500 b.…”