SPIRou: The second closest exoplanet in the habitable zone discovered just 11.4 light-years away

Just 11.4 light-years away, two exoplanets have been detected around a nearby star. One of them, Gl725Bc, is located in the habitable zone and is now the second closest potentially habitable planet to Earth. The other planet, Gl725Bb, is currently only a candidate exoplanet, meaning that more data is needed to confirm its detection. This breakthrough was made possible by SPIRou, a high-precision infrared spectropolarimeter developed by an international consortium led by IRAP in Toulouse, and a new innovative method for correcting disturbances caused by the Earth’s atmosphere.

M-type stars, or red dwarfs, are the most numerous stars in the Galaxy. Small, cold, and dim, they are ideal targets for detecting exoplanets, as their low mass makes the movements induced by orbiting planets more noticeable. It is around one of these stars, Gliese 725 B, located 11.4 light-years from Earth, that a system of two exoplanets has been discovered thanks to SPIRou, a very high-precision infrared spectropolarimeter installed on the Canada-France-Hawaii Telescope and developed by an international consortium led by IRAP in Toulouse.

The discovery is based on the radial velocity method, which measures the oscillations of a star under the effect of orbiting planets. This technique is particularly effective in infrared for red dwarfs, which emit most of their light in this range. But observing in infrared from the ground is complicated: water vapor and other components of the Earth’s atmosphere leave traces in the data that can mask planetary signals. To overcome this obstacle, researchers have developed an innovative method, called Wapiti, capable of correcting these disturbances. Using this approach, a first, relatively weak planetary signal has been detected with an orbital period of 4.8 days.

However, this signal is not statistically significant enough to confirm the existence of a planet. The associated object, Gl 725 Bb, is therefore currently considered only a candidate exoplanet. The Wapiti method has also revealed a more massive and better characterized planet, Gl 725 Bc, whose mass is at least 3.4 times greater than that of Earth and whose orbital period is 37.9 days. This planet is located in the habitable zone of its star, which means that if this planet is rocky and there is water in its composition, then this water must be in liquid form on its surface, one of the essential prerequisites for the possible formation of life. Gl 725 Bc receives an amount of energy comparable to that received by Mars, a planet on which water was present before the loss of most of its atmosphere, and is now the second closest planet in the habitable zone to Earth.

Although it does not transit in front of its star, which limits direct study of its atmosphere, its proximity and characteristics make it a prime target for next-generation instruments. This planet has characteristics that make it the second potentially rocky planet in the habitable zone that is least complex to study, after Proxima Centauri b, which is our closest exoplanet in the habitable zone.

For example, an instrument such as LIFE could enable such observations. LIFE is a space telescope project designed to directly study the atmospheres of nearby exoplanets by analyzing their infrared radiation, with the aim of searching for signatures of molecules such as water or other potential indicators of conditions favorable to life.

The study of this planet will, in the near future, provide a better understanding of the diversity of exoplanets capable of harboring liquid water on their surfaces, an essential prerequisite for the possible emergence of life elsewhere than on Earth. This discovery highlights the potential of high-precision infrared measurements in the search for habitable worlds around the nearest stars.

CNRS Laboratories involves

• Institut de Recherche en Astrophysique et planétologie (IRAP – OMP). Tutelles : CNRS / CNES / Université de Toulouse
• Institut de planétologie et d’astrophysique de Grenoble (IPAG – OSUG). Tutelles : CNRS / UGA
• Laboratoire d’astrophysique de Marseille (LAM – OSU Pythéas). Tutelles : CNRS / CNES / AMU
• Institut Univers, Théorie, Interfaces, Nanostructures, Atmosphère et environnement, Molécules (UTINAM – THETA). Tutelles :  CNRS / Univ Franche – Comté
• Institut d’astrophysique de Paris (IAP). Tutelles : CNRS / Sorbonne Université

Further Resource

• Scientific paper : M. Ould-Elhkim, C. Moutou, J.-F. Donati, P. Cortés-Zuleta, X. Delfosse, É. Artigau, C. Cadieux, P. Charpentier, A. Carmona, I. Boisse, C. Reylé, E. Gaidos, R. Cloutier, G. Hébrard, L. Arnold, J.-D. do Nascimento, N. J. Cook and R. Doyon, The SPIRou Legacy Survey – Detection of a nearby world orbiting in the habitable zone of Gl 725B achieved by correcting strong telluric contamination in near-infrared radial velocities with wapiti, A&A, 705 (2026) A234. 

IRAP Contacts

• Claire Moutou, claire.mourou@irap.omp.eu
• Jean-François Donati, Jean-Francois.Donati@irap.omp.eu