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.