Astronomers have discovered a "super-Earth" located just six light-years from our planet, orbiting the nearest lone star to our Sun. Named for its parent star, the exoplanet Barnard's Star b has a mass roughly 3.2 times that of the Earth, and a frigid surface temperature of -170 °C (-274 °F), making it an unlikely prospect in the search for extraterrestrial life.
The international team of astronomers behind the new discovery located the exoplanet using a massive dataset collected by seven cutting-edge instruments mounted on telescopes spread across the globe. The dataset, which is one of the most extensive of its kind ever compiled, spans 20 years of observations.
Barnard's Star is the fastest moving star in the night sky. To figure out whether the stellar speedster hosted an orbiting exoplanet, the scientists combed through the treasure trove of data in search of subtle shifts in the spectrum, or light, emitted by the star.
These shifts in wavelength could indicate a wobble in the star's trajectory created by the gravitational influence of a large rocky planet. A wobble away from Earth would be denoted by a shift toward a longer wavelength, while a wobble toward our Blue Marblewould be recorded in shorter wavelengths of emitted light.
These tiny perturbances can be measured with incredible accuracy. Data collected by the ESO's HARPS spectrograph – one of the instruments used to observe Barnard's Star – was able to track changes in velocity as small as 3.5 km/h (2.2 mph).
Observations made of Barnard's Star by HARPS and the six other instruments often overlapped. Having more than one eye on the wobbling giant allowed the team to compare and verify the findings made by individual telescopes.
"After a very careful analysis, we are 99 percent confident that the planet is there," said the team's lead scientist, Ignasi Ribas of the Institute of Space Studies of Catalonia and the Institute of Space Sciences in Spain. "However, we'll continue to observe this fast-moving star to exclude possible, but improbable, natural variations of the stellar brightness which could masquerade as a planet."
Based on their analysis, the astronomers conclude that Barnard's Star plays host to a large rocky exoplanet with a mass roughly 3.2 times that of the Earth. This would make the imaginatively-named Barnard's Star b the second-closest exoplanet to our Sun. Earth's closest exoplanet neighbor orbits four light-years away in the nearest stellar system to ours, Proxima Centauri.
Barnard's Star b orbits its parent star once every 233 days at a distance the equivalent of just 0.4 percent of the space separating the Earth and Sun. Despite its tight orbit, the enormous exoplanet receives just 2 percent of the energy that our home world receives from the Sun.
This is because Barnard's Star is a red dwarf. Compared to stars like our Sun, red dwarfs are relatively small and cool. Furthermore, the newly-discovered exoplanet is thought to orbit close to the red dwarf's snow line – the point at which water and other volatile compounds freeze solid.
The detection of a new neighboring exoplanet would fit a number of current theories on solar system formation. Super-Earths are thought to be the most common world to form around red dwarf stars, and the snow line would be the expected place for one to orbit.
Sadly, even if the evidence holds up, and such a planet does exist, the lack of energy and inhospitable temperatures mean that the dimly lit Barnard's Star b is unlikely to be capable of playing host to life as we know it.
A paper detailing the discovery is due to be published in the journal Nature on November 15th.
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