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Scientists find Earth-sized planet orbiting solar system's closest star Proxima Centauri

The planet called Proxima b is approximately 4.2 light-years away and has a mass of 1.17 earth masses
PUBLISHED JUN 5, 2020
Artistic impression of Proxima b orbiting Proxima Centauri (ESO/M Kornmesser)
Artistic impression of Proxima b orbiting Proxima Centauri (ESO/M Kornmesser)

The existence of an Earth-sized planet around the closest star in the solar system, Proxima Centauri, has been confirmed by an international team of scientists that includes researchers from the University of Geneva (UNIGE). The planet in question, Proxima b, has a mass of 1.17 earth masses and is located in the habitable zone of its star, which it orbits in 11.2 days.

"The Proxima Centauri star is an active red dwarf that bombards its planet with X rays, receiving about 400 times more than the Earth," the research says. While Proxima b is about 20 times closer to its star than the Earth is to the Sun, it receives comparable energy. If there is liquid form on the planet, it could harbor life, said researchers. The team, however, said that even though Proxima b is an ideal candidate for "biomarker research", there is still a long way to go before scientists can suggest that life has been able to develop on its surface. 

According to scientists, the current ‘breakthrough’ has been possible thanks to "radial velocity measurements of unprecedented precision" using Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO), the Swiss-manufactured spectrograph. ESPRESSO became operational in 2017, and is installed on the Very Large Telescope in Chile. Proxima b was first detected four years ago using an older spectrograph, HARPS — also developed by the Geneva-based team — which measured a low disturbance in the star's speed, suggesting the presence of a companion. Previously, scientists using the HARPS measurements said it was 1.3 Earth masses.

The detailed confirmation was made possible by the ESPRESSO spectrograph on the Very Large Telescope in Chile (Getty Images)

The team said in their analysis that ESPRESSO has made it possible to measure the mass of the planet with a precision of over one-tenth of the mass of Earth, which is unheard of. "The ESPRESSO spectrograph has performed radial velocity measurements on the star Proxima Centauri, which is only 4.2 light-years from the Sun, with an accuracy of 30 centimeters a second (cm/s) or about three times more precise than that obtained with HARPS, the same type of instrument but from the previous generation," said the study published in the journal Astronomy & Astrophysics.

"We were already very happy with the performance of HARPS, which has been responsible for discovering hundreds of exoplanets over the last 17 years. We're really pleased that ESPRESSO can produce even better measurements, and it's gratifying and just reward for the teamwork lasting nearly 10 years," said Francesco Pepe, a professor in the Astronomy Department in UNIGE's Faculty of Science and the person in charge of ESPRESSO.

The scientists are next going to tackle important questions such as whether there is an atmosphere that protects the planet from these deadly rays, and if this atmosphere exists, does it contain the chemical elements that promote the development of life. Meanwhile, the precision of the measurements made by ESPRESSO could result in another surprise, said the research team. They have found evidence of a second signal in the data, without being able to establish the definitive cause behind it. "If the signal was planetary in origin, this potential other planet accompanying Proxima b would have a mass less than one-third of the mass of the Earth. It would then be the smallest planet ever measured using the radial velocity method," said Pepe.

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