They discover a third planet in the closest star, Alpha Centauri.

They find a hot, rocky planet in our neighboring star, in which two other planets had already been discovered. It is

much smaller than Earth, and they still do not know if it has an atmosphere or is potentially habitable.

The closest star to the Sun, Alpha Centauri, hosts the third planet. It's called Proxima d, and it's much smaller than Earth, at a quarter of its mass. This new world, discovered by an international team made up of Spanish researchers, joins the other two exoplanets found around that star located just 4.3 light-years away: Proxima b and Proxima c. And everything seems to indicate that they are not the only ones in our closest galactic neighborhood.

"The discovery of Proxima d shows how little we know about planetary systems, even those so close to our own," María Rosa Zapatero Osorio, a researcher at the Center for Astrobiology (CAB, CSIC-INTA) and an of the discoverers of this world that they present today in the journal Astronomy & Astrophysics.

The big question, like every time an exciting and nearby exoplanet is discovered, is whether it could have liquid water and be habitable: "We still don't have the scientific answer to this question. Everything depends on the existence of a protective atmosphere since the life on Earth as we know it today is protected by our atmosphere", details the scientist.

As the researcher explains, "Proxima d orbits around its star within the habitable zone, an astrophysical term by which the region of interplanetary space in which water could be in liquid phase is known. Its equilibrium temperature is about 90 degrees warmer than the average temperature of the Earth. This makes it a "hot" world, but we don't know if it has an atmosphere."

A STAR COLDER AND SMALLER THAN THE SUN

As the author's detail, Proxima d is a rocky plant and is about four million kilometers from its star, which takes only five days to orbit: "It is very close to its star and the duration of "its year" is barely five days Let's not forget that the star Proxima Centauri is cooler and smaller than our Sun, so the Proxima planetary system is "scaled" to the size of the star, "he reviews.

To discover Proxima d, the researchers used the ESPRESSO high-precision spectrograph installed on the VLT telescope at Chile's European Southern Observatory (ESO). During observations to study Proxima b in detail, they found evidence of what turned out to be another planet. Researchers from the Institute of Astrophysics of the Canary Islands (IAC) have also participated in this research.

Finding a world with a mass like this says Zapatero, has been a challenge: "In this field of study, discovering planets as small as Proxima d is an arduous mission because its signal is very weak, and very specific instrumentation is required In the case of Proxima d, the amplitude of its signal is four times slower than the walking speed of the human being or only about 30 times faster than the speed of the garden snail", he compares.

The researcher does not doubt that the neighboring star hosts more worlds yet to be discovered. "In my popular science presentations I always insist that planets are the remnants of star formation (this also applies to Earth and the other planets in the Solar System). The clouds of gas and dust from which we come they collapse and fragment to form stars. The process is not entirely efficient, and the material that remains and remains around the stars ends up giving rise to planets, moons, comets and asteroids," he says.

ESO's future Extremely Large Telescope (ELT), currently under construction in Chile's Atacama Desert, will enable them to characterize the most exciting exoplanets in detail.

Will they use the James Webb Space Telescope to study the Proxima Centauri system? "Proxima d is too small even for James Webb, but it is possible that it will target Proxima in order to search for other higher-mass planets in orbits farther away than Proxima d," she says.