A third planet was detected in orbit of the star Proxima Centauri, the closest to the Solar System, according to a study published this Thursday 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.
The star Proxima Centauri is located four light-years away (equivalent to more than 125 million times the distance to the Moon). It is much smaller and twice as cold as it, 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.
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In the case of the system Proxima Centauri, when observed from Earth, the bodies that orbit the star are in another planewhich prevents the application of the so-called “transit” method -the easiest- that detects planets by measuring the variations in luminosity caused by the passage of a body, causing a micro-eclipse.
It has therefore been necessary to resort to the method of radial velocities, which is based on measuring the oscillations of the star due to the micro-effect of gravity of an orbiting body.
This is how Proxima b, with a mass similar to Earth, and located in the “habitable” zone (neither too close nor far from the star), and Proxima c, smaller, were found a few years ago.
Suspicion of a third planet
“When we discovered them, we suspected an influence” of a third planet, Baptiste Lavie, from the astronomy department of the University of Geneva, a member of the team that uses the Very Large Telescope (VLT, literally “very large telescope”), told AFP. of the European Southern Observatory (ESO) in Chile.
But this signal was so weak that it was necessary to continue the observations with the help of the ESPRESSO spectrograph installed on the VLT. These observations confirmed a tiny variation in the speed of the star (1.4 km per hour) caused by a nearby planet.
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Proxima d is 4 million kilometers from its star, less than a tenth of Mercury’s distance from the Sun.
Situated on the edge of the habitable zone, Proxima d takes only five days to complete its revolution.
“Undoubtedly it is a rocky planet, because its mass is too weak to retain the gass” as do the gas giants of the solar system that are Jupiter or Saturnaccording to astronomer Baptiste Lavie.
“This major discovery demonstrates the potential of the radial velocity method to reveal the existence of light planets, like this one (…) capable of harboring life,” according to Pedro Figuiera, head of the ESPRESSO instrument in Chile, quoted in an ESO statement . (I)
Source: Eluniverso
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