'Super-earth' found orbiting Sun's nearest solitary star

LONDON: Astronomers have discovered a frozen 'super Earth' orbiting the closest solitary star to the Sun, a breakthrough that could shine light on our planet's nearest planetary neighbours.

The potentially rocky planet, known as Barnard's star b, is a 'superearth' and orbits around its host star once every 233 days, said researchers from Queen Mary University of London in the UK.

The findings, published in the journal Nature, show the planet lies at a distant region from the star known as the 'snow line'.

This is well beyond the habitable zone in which liquid water, and possibly life, could exist, researchers said.

The planet's surface temperature is estimated to be around minus 170 degrees Celsius, meaning it is likely to be a frozen world which is uninviting to Earth-like life, they said.

However, if the planet has a substantial atmosphere the temperature could be higher and conditions potentially more hospitable.

"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. Hopefully we got it right this time," said Guillem Anglada Escude from Queen Mary's School of Physics and Astronomy. "If the planet can be observed directly it will provide vital information about its properties and extend our understanding of the kinds of planets that form around red dwarf stars," researchers said.

At nearly six light-years away Barnard's star is the next closest star to the Sun after the Alpha Centauri triple system. It is a type of faint, low-mass star called a red dwarf. Red dwarfs are considered to be the best places to look for exoplanet candidates, which are planets outside our solar system.

Barnard's star b is the second closest known exoplanet to our Sun. The closest lies just over four light-years from Earth.

That exoplanet, called Proxima b, orbits around the red dwarf star Proxima Centauri.

The researchers used the radial velocity method during the observations that led to the discovery of Barnard's star b.

This technique detects wobbles in a star which are likely to be caused by the gravitational pull of an orbiting planet.

These wobbles affect the light coming from the star.

As the star moves towards the Earth its spectrum appears slightly shifted towards the blue and, as it moves away, it is shifted towards the red.

This is the first time that this technique has been used to detect a planet this small so far away from its host star.

The researchers re-examined archive data obtained over a 20-year period, and added new observations with the latest generation of instruments.

This wealth of data provided the extraordinary accuracy needed to identify the influence of the planet with near certainty.

The wobble observed in the star's motion corresponds to speeds of only just over one metre per second -- about walking speed.

"After a very careful analysis, we are over 99 per cent confident that the planet is there, since this is the model that best fits our observations," said Ignasi Ribas from the Institute of Space Sciences in Spain.