Exoplanets, -moons, -comets

The RoPES Project With HARPS and HARPS-N II. A Third Planet In The Multi-planet System HD 176986

By Keith Cowing

Status Report

astro-ph.EP

January 29, 2026

Filed under astro-ph.EP, Earth-like exoplanet, exoplanet, Habitable Zone, HARPS, HARPS-N, HD 176986, HD 176986 b, HD 176986 c, HD 176986 d, imaging, K-type star, mini-Neptunes, Sun-like star, super-Earth

The RoPES Project With HARPS and HARPS-N II. A Third Planet In The Multi-planet System HD 176986 — Time series of RV and activity indicators. Panel (a): RV time series. Panel (b): GLS periodogram related to the RV time series. We see two prominent peaks in correspondence with the two planets detected in Suárez Mascareño et al. (2018). Panels (c), (e), (g), (i), and (k): Activity indicators time series. Panels (d), (f), (h), (j), and (l): Corresponding GLS periodograms. The red, green, and blue lines in the periodogram indicate a power corresponding to a 10%, 1%, and 0.1% FAP, respectively. Panels (c) and (d): FWHM. We see a strong peak in the GLS periodogram at 2331.89 d. Panels (e) and (f): Bisector. The strongest peak in the GLS periodogram is at 17.9 d period. This peak is likely related to stellar rotation. A weaker peak at FAP ∼ 10 % in correspondence with the magnetic cycle is also visible at a long period. Panels (g) and (h): S index. In panel (h) we see again a strong peak at 2331.89 d, caused by the magnetic cycle. In panels (i) and (j), we see the time series and the GLS periodogram of Hα. We see again a peak at 2331.89 d due to the magnetic cycle of the star. Panels (k) and (l): Time series and the GLS periodogram of Contrast. We can also find in this dataset the signature of the magnetic cycle in the peak at 2331.89 d in the GLS periodogram. FWHM, S index, Hα, and Contrast all show an additional peak at ∼ 35 d. This peak is related to the rotation period of the star as shown in the analysis of stellar activity. — astro-ph.EP

Context. Earth-like planets orbiting in the habitable zone of K- to G-type stars create an RV effect in amplitude of less than 1 m s⁻¹ and have orbital periods of hundreds of days. Only long-term RV surveys with sub-meter per second precision instruments can explore the outer regions of Sun-like stars and look for Earth-like planets and super-Earths.

Detecting Earth-like or super-Earth planets in the habitable zone of Sun-like stars is crucial to provide targets to the next generation of direct imaging facilities. Aims. We present the analysis of the K-type star HD 176986. It has a brightness of V=8.45 mag and a distance from the Sun of d = 27.88 pc. This star hosts a known planetary system of two super-Earths. We utilize historical and recently collected RV measurements to investigate the presence of Earth- and super-Earth-like planets in the habitable zone of HD 176986.

Methods. We monitored the system with HARPS and HARPS-N. We joined historical datasets with new data collected in an ongoing blind search program. We took advantage of recently developed tools for RV extraction and stellar activity filtering. The analysis of activity indicators permits us to determine the period of the magnetic cycle of the star alongside its rotation period. We performed a joint analysis of RVs and activity indicators through multidimensional GPs to better constrain the activity model in RVs and avoid overfitting.

Results. We de tected a new planet orbiting the star and retrieved the two known planets. HD 176986 b has an orbital period of 6.49164+0.00030 −0.00029 d and a minimum mass of 5.36 ± 0.44 M_⊕. HD 176986 c has an orbital period of Pc = 16.8124 ± 0.0015 d and a minimum mass of 9.75+0.65 −0.64 M_⊕. HD 176986 d has an orbital period of 61.376+0.051 −0.049 d and a minimum mass of 6.76+0.91 −0.92 M_⊕. From the analysis of activity indicators, we find evidence of a magnetic cycle with a period of 2432+64 −59 d, along with a rotation period of 36.05 +0.67 −0.71d.

Conclusions. We discover a new planet in the multi-planet system orbiting the K-type star HD 176986. All the planets have minimum masses compatible with super-Earths or mini-Neptunes.

N. Nari, A. Suárez Mascareño, J. I. González Hernández, A. K. Stefanov, R. Rebolo, J. M. Mestre, X. Dumusque, M. Cretignier, V. M. Passegger, L. Mignon

Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2601.20559 [astro-ph.EP](or arXiv:2601.20559v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2601.20559
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Related DOI:
https://doi.org/10.1051/0004-6361/202557287
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Submission history
From: Nicola Nari
[v1] Wed, 28 Jan 2026 12:53:04 UTC (5,881 KB)
https://arxiv.org/abs/2601.20559
Astrobiology

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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