A low-eccentricity migration pathway for a 13-h-period Earth analogue in a four-planet system (original) (raw)
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 (Extended Data Figs. 4-6). 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
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