RedDots: Multiplanet system around M dwarf GJ 887 in the solar neighborhood

¹ Institut für Astrophysik und Geophysik (IAG), Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
² Centre for Exoplanet Science, SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
³ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
⁴ School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
⁵ Private Astronomer
⁶ Institut de Ciències de I’Espai (ICE-CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Cerdanyola del Vallès, Barcelona, Catalonia, Spain
⁷ INAF, Osservatorio Astrofisico di Catania, via Santa Sofia, 78 Catania, Italy
⁸ Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 1 April 2025
Accepted: 23 December 2025

Abstract

GJ 887 is a bright M dwarf in the solar neighborhood with two currently reported nontransiting exoplanets with periods of 9 d and 21 d, along with an additional unconfirmed signal at 50 d. We reanalyzed the system with 101 new HARPS and 12 new ESPRESSO radial velocities (RVs) secured with a cadence to confirm or refute the origin of the 50 d signal. To do so, we searched for signals related to stellar activity in photometric data and spectroscopic indicators. We modeled the stellar activity in the RVs with Gaussian processes (GPs). With the Bayesian analysis, we confirmed a four-planet model, including the two previously known planets at periods of 9.2619 ± 0.0005 d and 21.784 ± 0.004 d, as well as two newly confirmed exoplanets: an Earth-mass planet, with a 4.42490 ± 0.00014 d period and a sub-meter-per-second amplitude, and a super-Earth with a 50.77 ± 0.05 d period located in the habitable zone (HZ). This super-Earth is the second closest planet in the HZ, after Proxima Cen b. We found an additional signal in a 2:1 resonance with the 4.4 d planet at 2.21661 ± 0.00010 d with an amplitude of 0.37 ± 0.09 m/s, which could be related to an additional planet. However, other explanations of its origin are also plausible. This signal remains a candidate, as further investigation is required to confirm its true nature. If the signal is caused by a planet, its minimum mass would be half that of Earth. We measured the stellar rotation period with the characteristic periodic timescale of the GP. We found a period of 38.7 ± 0.5 d, which is consistent with the rotation period determined from photometry and other activity indices.