Astronomers have found evidence of an Earth-mass planet, with a temperature suitable for the existence of liquid surface water, orbiting in the habitable zone of the star closest to Earth, Proxima Centauri, according to new research published Thursday in the journal Nature.
The newly-discovered planet, designated Proxima b, orbits its cool red host star once every 11 days, is slightly more massive than Earth and is the exoplanet located closest to our homeworld, and Dr. Guillem Anglada-Escudé of Queen Mary University of London and his colleagues said that it might also be the nearest possibly life-bearing planet beyond the solar system.
Proxima Centauri is a red dwarf located just four light-years from the solar system, and while it is too faint to be observed by the naked eye, the study authors explained. However, using a series of instruments including the European Southern Observatory (ESO) 3.6-metre telescope in Chile, the astronomers were able to identify the potentially habitable planet by searching for the minute wobbling from the star indicative of an orbiting world’s gravitational pull.
“The first hints of a possible planet were spotted back in 2013,” Anglada-Escudé explained in a statement, “but the detection was not convincing. Since then we have worked hard to get further observations of the ground with help from ESO and others. The recent Pale Red Dot campaign has been about two years in the planning.”
Discovering ‘the closest potential Earth-analogue’ planet
The Pale Red Dot campaign is the name given to an effort to detect Earth-like planets orbiting Proxima Centauri, and the researchers involved provided regular online updates of their progress through their website and social media. Their data, combined with a previous observation made at ESO observatories and other facilities, was what led to Proxima b’s discovery.
Anglada-Escudé and his colleagues found that, Proxima Centauri sometimes approaches Earth at a speed of about 5 km/hour (3.1 mph) and sometimes moves away at a similar pace. This regular pattern repeats every 11.2 days, and by carefully analyzing the tiny Doppler shifts produced as a result of this activity, the researchers found that they indicated the presence of a planet that had a mass at least 1.3 times that of Earth’s, orbiting approximately 7 million km (4.35 million miles) from Proxima Centauri – a fraction of the distance separating the Earth and the Sun.
“I kept checking the consistency of the signal every single day during the 60 nights of the Pale Red Dot campaign. The first 10 were promising, the first 20 were consistent with expectations, and at 30 days the result was pretty much definitive,” Anglada-Escudé said. While Proxima b orbits its star at a distance closer than that of Mercury, he noted that its host star is much fainter than our sun, and thus the potential habitability of the new world cannot be dismissed.
“Many exoplanets have been found and many more will be found, but searching for the closest potential Earth-analogue and succeeding has been the experience of a lifetime for all of us,” the study author continued. “The search for life on Proxima b comes next,” he added. That search will involve additional observations using both current equipment and next-gen instruments like the forthcoming European Extremely Large Telescope (E-ELT).
Image credit: ESO/M. Kornmesser