Proxima Centauri is the nearest star to our solar system, and a team of astronomers using the European Southern Observatory’s (ESO’s) Very Large Telescope (VLT) in Chile has discovered evidence of another planet around it.
This candidate planet, which has been found to orbit this star three times, is the lightest one to date. The planet is also one of the lightest exoplanets yet discovered, weighing only around a fourth of Earth’s mass.
“The discovery shows that our closest stellar neighbor seems to be packed with interesting new worlds, within reach of further study and future exploration,” explains João Faria, a researcher at the Instituto de Astrofísica e Ciências do Espaço, Portugal, and lead author of the study published today in Astronomy & Astrophysics.
The star Proxima Centauri, which is a little over four light-years from the Sun, is the nearest one. Less than a tenth of Mercury’s distance from the Sun, the newly discovered planet Proxima d orbits Proxima Centauri at a distance of around four million kilometers.
It takes only five days to complete one orbit around Proxima Centauri and circles between the star and the habitable zone the region around a star where liquid water can exist on the surface of a planet.
The star is already known to be home to two other planets: candidate Proxima c, which is on a longer five-year orbit around the star, and Proxima b, an Earth-mass planet that orbits the star every 11 days and is in the habitable zone.
This achievement is extremely important. It shows that the radial velocity technique has the potential to unveil a population of light planets, like our own, that are expected to be the most abundant in our galaxy and that can potentially host life as we know it.
Pedro Figueira
A few years ago, Proxima b was found using the HARPS instrument on the 3.6-meter ESO telescope. The Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO), a new instrument on ESO’s VLT with improved precision, was used to investigate the Proxima system in 2020, confirming the discovery.
The first indications of a signal belonging to an object with a five-day orbit were discovered during these more recent VLT studies. The signal was so feeble that the scientists needed to make additional observations with ESPRESSO to be certain it was coming from a planet and not just because the star had changed.
“After obtaining new observations, we were able to confirm this signal as a new planet candidate,” Faria says. “I was excited by the challenge of detecting such a small signal and, by doing so, discovering an exoplanet so close to Earth.”
Proxima d surpasses a planet recently found in the L 98-59 planetary system to become the lightest exoplanet ever measured using the radial velocity technique, with a mass of only one-fourth that of Earth.
The method detects minute jitters in a star’s velocity brought on by the gravitational pull of an orbiting planet. Proxima D’s gravitational pull is so negligible that it barely moves Proxima Centauri back and forth at a rate of about 40 centimeters per second (1.44 kilometers per hour).
“This achievement is extremely important,” says Pedro Figueira, ESPRESSO instrument scientist at ESO in Chile. “It shows that the radial velocity technique has the potential to unveil a population of light planets, like our own, that are expected to be the most abundant in our galaxy and that can potentially host life as we know it.”
“This result clearly shows what ESPRESSO is capable of and makes me wonder about what it will be able to find in the future,” Faria adds. ESO’s Extremely Large Telescope (ELT), now being built in the Atacama Desert, will be essential to finding and researching many more planets around neighboring stars, complementing ESPRESSO’s hunt for extraterrestrial life.
