Paris. A third planet was detected in the orbit of the star Proxima Centauri, the closest to the solar system, according to a study published yesterday in Astronomy & Astrophysics.
With barely a quarter of the mass of Earth, Proxima D is one of the lightest in the catalog of exoplanets, which has about 5,000 bodies orbiting other stars.
Proxima Centauri is located four light years away (more than 125 million times the distance to the Moon) and belongs to the category of “red dwarfs”.
The detection of exoplanets is very difficult, since they are very far away and are very dim.
In the case of the Proxima Centauri system, when observed from Earth, the bodies that orbit it are in another plane, which prevents the application of the so-called “transit” method –the easiest one– that detects planets by measuring the variations in luminosity caused by the passage of a body, causing a microeclipse.
It has been necessary to resort to the method of radial velocities, which is based on measuring the oscillations of the star due to the microeffect of gravity of a body that orbits it.
This is how Proxima B, with a mass similar to Earth, located in the “habitable” zone, and Proxima C, smaller, were found a few years ago.
“When we discovered them, we suspected the influence” of a third planet, said Baptiste Lavie, from the astronomy department at the University of Geneva, a member of the team using the European Southern Observatory’s Very Large Telescope (VLT). in Chile.
However, this signal was so weak that it was necessary to continue the observations with the help of the spectrograph. espresso installed on the VLT. These observations confirmed a minute variation in the speed of the star (1.4 kilometers per hour) caused by a nearby planet.
Proxima D is 4 million kilometers from its star, less than a tenth of the distance between Mercury and the Sun.
Situated on the edge of the habitable zone, it takes only five days to complete its revolution.
“It is a rocky planet, because its mass is too weak to retain gas” as do the giants of the solar system: Jupiter or Saturn, according to Baptiste Lavie.
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