One of the closest stars to our Sun hosts a planet astronomers have announced.
The so-called super Earth orbiting Barnard's star, the fourth closest star to the sun. Only the Alpha Centauri triple system is closer.
The planet, Barnard's star b, and its host star are located six light-years from Earth. The alien world is likely a rocky planet, boasting a mass 3.2 times that of Earth. Barnard's star b completes an orbit around its sun every 233 days.
Nearby planets like this are likely to be prime targets in the search for signatures of life, using the next generation of telescopes.
The star is an extremely faint "red dwarf" that's about 3% as bright as the Sun. Barnard's Star b, is about as far away from its star as Mercury is from the Sun.
The super Earth orbits past a boundary called the "snow line", beyond the traditional habitable zone, positioned too far from its star to host liquid water. Any water found on the exoplanet would be frozen. Scientists estimate the planet features a surface temperature of negative 170 degrees Celsius, though it's possible a substantial atmosphere allows for slightly milder temperatures, making conditions more hospitable to life.
Astronomers described their discovery of Barnard's star in a paper published Wednesday in the journal Nature.
"Barnard's star is an infamous object among astronomers and exoplanet scientists, as it was one of the first stars where planets were initially claimed but later proven to be incorrect," Guillem Anglada Escudé, an astrophysicist at Queen Mary University of London, said in a news release. "Hopefully we got it right this time."
Scientists confirmed the exoplanet's presence using the radial velocity method, measuring slight stellar oscillations caused the super Earth's gravitation pull as it orbits the star.
Astronomers found a consistent 'wobbling' pattern in both archival data and newly collected spectral data. They also added new observations with the Carmenes spectrometer in Almeria, Spain, the Eso/Harps instrument in Chile and the Harps-N instrument in the Canary Islands.
These wobbles also affect the light coming from the star. As it moves towards Earth its light appears shifted towards the blue part of the spectrum and, as it moves away, it appears shifted towards the red.
"After a very careful analysis, we are over 99 percent confident that the planet is there, since this is the model that best fits our observations," said Ignasi Ribas, astronomer at the Institute of Space Sciences in Spain. "However, we must remain cautious and collect more data to nail the case in the future."
In the future, scientists hope to observe the exoplanet directly using new instruments and observatories, like NASA's planned Wide Field Infra Red Survey Telescope. Direct observations could help scientists better characterise the exoplanet's size, mass and composition, as well as reveal details about its atmosphere.
"If you take the specs of how it should perform, it should easily image this planet. When we have the image we can then start to do spectroscopy - looking at different wavelengths, in the optical, in the infrared, looking at whether light is absorbed at different colours, meaning there are different things in the atmosphere." said Dr Anglada Escudé.
The new data contain tentative hints of a second planet orbiting Barnard's Star even further out than the Super-Earth. This will be confirmed or not with followup studies.
The star is named after the American astronomer E E Barnard, who measured properties of its motion in 1916.