A team of astronomers using the Very Large Telescope at the European Southern Observatory (ESO’s VLT) in Chile has found evidence of another planet orbiting Proxima Centauri, the closest star to our system solar. Proxima Centauri is the closest star to the Sun, located just over four light years away. The newly discovered planet, named Proxima d, orbits Proxima Centauri at a distance of regarding four million kilometers, less than a tenth of Mercury’s distance from the Sun. This candidate planet is the third detected in the system and the lightest ever discovered orbiting this star. At just a quarter of the mass of Earth, the planet is also one of the lightest exoplanets ever discovered. These results are published in the journal Astronomy & Astrophysics.
“The discovery shows that our closest stellar neighbor appears to be teeming with interesting new worlds, within the scope of further study and future exploration,” said Joao Faria, a researcher at the Instituto de Astrofisica e Ciencias do Espaco, in Portugal, in a press release.
Proxima d orbits between the star and the habitable zone – the area around a star where liquid water can exist on a planet’s surface – and takes just five days to orbit Proxima Centauri.
The star system is already known to host two other planets: Proxima b, a planet with a mass comparable to that of Earth that orbits the star every 11 days and is in the habitable zone, and the candidate Proxima c , which is on a longer five-year orbit around the star.
Proxima b was discovered a few years ago using the HARPS instrument on ESO’s 3.6-meter telescope.
The discovery was confirmed in 2020 when scientists observed the Proxima system with a new instrument on ESO’s VLT that had higher precision, the SPectrograph Echelle for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO).
It was during these more recent VLT observations that astronomers spotted the first hints of a signal corresponding to an object with a five-day orbit. Because the signal was so weak, the team had to do follow-up observations with ESPRESSO to confirm it was due to a planet, and not just changes in the star itself.
“After obtaining new observations, we were able to confirm this signal as a new candidate planet,” Faria said.
At just a quarter of Earth’s mass, Proxima d is also the lightest exoplanet ever measured using the radial velocity technique, surpassing a recently discovered planet in the L 98-59 planetary system.
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