(Paris) It is only six light years away, a year lasts three Earth days and it is 125°C. Astronomers have discovered an exoplanet around Barnard’s star, one of the closest to our Sun.
The discovery, published Tuesday in the journal Astronomy and Astrophysics, is the result of five years of observations carried out using the Very Large Telescope (VLT) in the Atacama Desert (Chile).
The team of astronomers from the European Southern Observatory (ESO) was looking for signals from possible exoplanets located in the “habitable zone” of Barnard’s star, that is to say the zone where water can exist in a liquid state on the surface of the planet. A condition considered essential for the emergence of life.
This is, however, not the case for “Barnard b”, the name given to the new exoplanet. Twenty times closer to its star than Mercury is to our Sun, it completes its year by circling its star in 3.15 days and its surface temperature is around 125°C.
“Barnard b is one of the least massive exoplanets known and one of the few with a mass less than that of Earth. But the planet is too close to the host star” to be in the habitable zone, underlines in an ESO press release, Jonay González Hernández, researcher at the Canary Islands Institute of Astrophysics (Spain) and lead author of the ‘study.
“Even though the star is cooler than our Sun by about 2,500 degrees, it is too hot to maintain liquid water on the surface,” he adds.
Red dwarf
Located in the constellation Slytherin, Barnard’s star is the second closest star system to us after the group of three stars of Alpha Centauri, about six light years away, or 56.8 trillion kilometers. .
In addition to its proximity, this star constitutes a privileged target in the search for exoplanets similar to Earth, because it is a red dwarf, a cold star.
Its “habitable zone” is much closer to it than that of hotter stars, like the Sun. Planets in this zone therefore have shorter orbital periods, allowing astronomers to monitor them for a few days or weeks, rather than for years.
Because red dwarfs are much less massive than the Sun, they are more easily disrupted by the gravitational pull of the planets around them, causing them to wobble more strongly.
When a planet orbits a star, it exerts a small gravitational force on the latter which causes it to oscillate and move closer or further away from our planet, which can be measured from Earth with spectrographs.
It is this “radial velocities” method that was used to detect “Barnard b”. These observations were then confirmed by data from other instruments dedicated to the hunt for exoplanets.
In addition to “Barnard b”, the research team found evidence of three other potential exoplanets orbiting the same star, which will need additional observations to be confirmed.
“The discovery of this planet, as well as other previous discoveries such as Proxima b and d (two exoplanets orbiting Proxima Centauri, Editor’s note), shows that our cosmic backyard is full of low-mass planets,” notes Alejandro Suárez Mascareño, researcher at the Canary Islands Institute of Astrophysics and co-author of the study, cited in the press release.
Since the discovery of the first exoplanet, 51-Pegasi-b, in 1995 at the Haute-Provence Observatory (south-east of France), some 5,700 planets have been identified outside our solar system. But only a handful are considered to be located in their star’s habitable zone.