Astronomers discover ‘super-Earth’ six light years away

Cristina Cross
November 16, 2018

Think of it this way: If planets were rare, you wouldn't expect to see many around nearby stars.

Barnard's Star has always been "the great white whale" of exoplanet hunting, said Carnegie astronomer Paul Butler, a co-author on the Nature paper.

Barnard's star has been observed extensively over the years, partly because it's so close, partly because it's a prototypic example of a red dwarf star. This red dwarf, smaller and older than our Sun, is among the least active red dwarfs known, so it represents an ideal target to search for exoplanets. The letter "b" is the suffix showing it is the first planet in the system-for example, if there were another planet in this system, it would likely be called Barnard's Star c. The astronomers calculate that the newfound world, dubbed Barnard's star b, is about 3.2 times the mass of Earth and orbits its host star once every 233 days.

Professor Carole Haswell, head of astronomy at the Open University and a member of the global team that announced the discovery in the journal Nature, said: "While the starlight from Barnard's Star is too feeble for Barnard's Star b to have liquid water on its surface, Barnard's Star b probably has a similar temperature to Jupiter's moon Europa". The newly discovered one is the second closest to our solar system ever found. 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.

Red dwarfs are far smaller and cooler than our own star, and thus emit far less heat.

The European Space Agency's Gaia Space Observatory may be able to make detections that would further confirm the presence of a planet around Barnard's Star, he said, but those data aren't expected to be released until the 2020s. While the star itself is ancient - probably twice the age of our Sun - and relatively inactive, it also has the fastest apparent motion of any star in the night sky.

Ribas, who is the director of the Institute of Space Studies of Catalonia and a research at Spain's Institute of Space Sciences, noted that there have been many previous searches for planets around Barnard's Star, and even announcements of discoveries.

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"This freezing, shadowy world could have a temperature of 170 [degrees Celsius], making it inhospitable for life as we know it", read the statement. "Hopefully we got it right this time". The timing of the signal indicates that the planet orbits at about the same distance as Mercury orbits our Sun. The only stars closer are the triplet stars of the Alpha Centauri system, which is mainly visible in the southern sky.

A handout picture released by the European Southern Observatory (ESO) on November 13, 2018, shows an artist's impression of a "Super-Earth" planet viewed from space. For most of the past hundred years, the only way was the astrometric technique, in which astronomers look for the host star to wobble relative to background stars, Butler said. "The combination of all data led to a total of 771 measurements", Ribas said. Their analysis suggested there might be a signal of something orbiting with a 230 day period, but the data suffered from what the researchers term "very poor sampling".

But that icy orbit adds to our confidence that the planet could really be there.

Even if Barnard's star b is rocky, life would have a hard time taking root on its chilly surface.

The team was looking for signs that Barnard's star was shifting back and forth due to the gravitational pull of a planet, a planet-hunting approach called the radial velocity method.

A planet has been detected orbiting Barnard's Star, a mere 6 light-years away. This means that astronomers are getting better at finding these kinds of planets outside our solar system.

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