Two Planets Around a Dim Neighbor express
The red dwarf Gliese 725 B lies just 3.5 light-years away — by cosmic standards, a neighbor next door. Such stars are small and dim, so planets around them are easier to spot: the star wobbles more noticeably under their gravitational pull. But Earth's own atmosphere gets in the way of detecting that wobble. It adds extra lines to the star's spectrum, like a dirty window adding smudges to a photograph.
The scientists applied a cleaning method called WAPITI. It works like a smart filter that separates the constant "fingerprint" of Earth's atmosphere from the star's genuine oscillations. First, they tested the method on synthetic data, planting planet signals in it, and it found them correctly. Then they applied it to real observations of the star taken with the SPIRou spectrograph. It turned out that two planets orbit Gliese 725 B.
The inner one, Gliese 725 Bb, completes an orbit in 4.8 days, while the outer one, Gliese 725 Bc, takes 37.9 days. The outer planet falls in the habitable zone: not too hot, not too cold, and water could remain liquid. Its mass is about 3.5 times Earth's, most likely a rocky world. The inner planet is lighter, at roughly 1.5 Earth masses.
Red dwarfs flare, and those flares also shake the star. To avoid mistaking them for planets, the scientists modeled the star's activity. This also helped measure its rotation: one spin every 105 days. So the dirty window got cleaned, and behind it were two new planets around our nearest neighbor.
Original abstract
as written by the authors arXiv:2601.22815
M dwarfs are prime targets in the search for exoplanets because of their prevalence and because low-mass planets can be better detected with radial velocity (RV) methods. In particular, the near-infrared (NIR) spectral domain offers an increased RV sensitivity and potentially reduced stellar activity signals. Howevern precise NIR RV measurements can be strongly affected by telluric absorption lines from the Earth's atmosphere. We searched for planets orbiting Gl 725 B, a nearby late-M dwarf at $$3.5$$ pc, using high-precision SPIRou RV observations. We assessed the impact of telluric contamination and evaluated the performance of the weighted principal component analysis reconstruction method (WAPITI), designed to mitigate these systematics and improve planet detectability. Using synthetic and observational SPIRou data, we simulated telluric effects on RVs under varying barycentric Earth radial velocity (BERV) conditions and applied WAPITI to correct line-by-line RVs. The method was tested through injection-recovery experiments and applied to real SPIRou observations of Gl 725 B. WAPITI efficiently corrects telluric contamination in simulated and real datasets, enhancing the detectability and accuracy of planetary signals. We identify a two-planet system around Gl 725 B composed of a candidate inner planet (Gl 725 Bb) with a period of $$4.765 \pm 0.004$$ days and semi-amplitude $$1.4 \pm 0.3$$ m.s$$^{-1}$$, and a confirmed outer planet (Gl 725 Bc) with a period of $$37.90 \pm 0.17$$ days and semi-amplitude $$1.7 \pm 0.3$$ m.s$$^{-1}$$. Their minimum masses are $$1.5 \pm 0.4$$ and $$3.5 \pm 0.7$$ M$$_\oplus$$, respectively, and the outer planet lies in the habitable zone. Using a multi-dimensional Gaussian process framework to model stellar activity, we also recover a stellar rotation period of $$105.1 \pm 3.3$$ days.
Gliese 725 B is one of the closest stars to us: light takes just 3.5 years to reach us, whereas it takes 26,000 years to reach the center of the Galaxy.
In Isaac Asimov's story "Nightfall," a planet around a red dwarf turns out to be in a system with six suns, but Gliese 725 B is more modest: one dim star and two planets.