The existence of an Earth-sized exoplanet around the closest star to our sun, Proxima Centauri, has been confirmed by an international team of astronomers, including researchers from the University of Geneva.

The findings, which were published in the journal Astronomy & Astrophysics, reveal that Proxima b has a mass of 1.17 Earth masses and is located in the habitable zone of its star, located 4.2 light-years from our sun. The planet completes one orbit every 11.2 Earth days.

This breakthrough was possible thanks to the radial velocity measurements of ESPRESSO, an ultra-powerful spectrograph that is part of the Very Large Telescope in Chile. ESPRESSO stands for Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations.

The ESPRESSO instrument can be three times more precise in its measurements than HARPS, which is a previous-gen model.

“We were already very happy with the performance of HARPS, which has been responsible for discovering hundreds of exoplanets over the last 17 years,” the study’s co-author Francesco Pepe, a University of Geneva professor in the astronomy department, said in a statement.

“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.”

Although Proxima b is about 20 times closer to its star than Earth is to its sun, it still receives a comparable amount of energy, which means that there is a chance that water could exist in liquid form. For scientists, any environment with water is a strong candidate for life.

“Confirming the existence of Proxima b was an important task, and it’s one of the most interesting planets known in the solar neighborhood,” the study’s main author Alejandro Suarez Mascareño said in a statement.

Astronomers, however, are keeping in mind that Proxima Centauri is an active red dwarf that bombards its planet with X-rays at levels that are 400 times higher than on Earth.

In the meantime, ESPRESSO has given astronomers another surprise. The team has found evidence of a second signal in the data, although they have yet 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,” Pepe said. “It would then be the smallest planet ever measured using the radial velocity method.”

Ethen Kim Lieser is a Science and Tech Editor for the National Interest.