Second-closest ‘super-Earth’ found orbiting sun’s stellar twin

15 Nov 2018

An artist’s impression of the surface of Barnard’s star b. Image: ESO/M Kornmesser

In a major discovery, astronomers have located a so-called ‘super-Earth’ orbiting the nearest single star to the sun.

An international team of astronomers was excited to announce the discovery of a super-Earth – 3.2 times the size of our own – orbiting a star just six light years away called Barnard’s star. This new planet – designated Barnard’s star b – now becomes the second-closest known exoplanet to Earth and details of what it may look like have been published in Nature.

Orbiting its host star approximately every 233 days, Barnard’s star b is very close to its parent star at a distance only 0.4 times that between Earth and the sun. However, the planet lies close to the so-called snow line, where volatile compounds such as water can condense into solid ice.

With freezing temperatures as low as -170 degrees Celsius and a largely shadowed existence for much of its surface, the researchers said the planet would be totally inhospitable for life as we know it.

Named after astronomer Edward Emerson Barnard, the star is a cool, low-mass red dwarf providing the exoplanet with only 2pc of the energy that the Earth receives from the sun. While almost twice as old as the sun, Barnard’s star is relatively inactive and has the fastest apparent motion of any star in the night sky.

Artist's impression of Barnard star b orbiting its parent star.

An artist’s impression of the ‘super-Earth’ Barnard star b orbiting its parent star. Image: ESO/M Kornmesser

A huge amount of information

This is not the first time that Barnard’s star has been the focus of attention for exoplanet-hunting astronomers. However, until now, nothing had been found. The discovery was only made possible by combining measurements from several high-precision instruments mounted on telescopes all over the world.

“After a very careful analysis, we are 99pc confident that the planet is there,” stated 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.”

Among the instruments used to locate the planet were the European Southern Observatory’s planet hunters, the HARPS and UVES spectrographs, which, in combination with the Doppler effect, were able to see when the planet’s gravitational pull resulted in the star wobbling.

“We used observations from seven different instruments, spanning 20 years of measurements, making this one of the largest and most extensive datasets ever used for precise radial velocity studies,” said Ribas.

“The combination of all data led to a total of 771 measurements – a huge amount of information!”

Colm Gorey was a senior journalist with Silicon Republic