Chilly 'super-Earth' may orbit Sun’s nearest single star neighbour

Christopher Davidson
November 15, 2018

Super-Earths are like nothing we have in our solar system and have only been discovered orbiting other stars more distant than Barnard's Star. As for the possibility of life on Bernard's Star b, the planet is "way too cold" to sustain liquid water, Ribas says, and whether life may be frozen beneath an ocean is just speculation at this point.

Graphic representation of the relative distances to the nearest stars from the sun.

Although it is about as close to its own star as Mercury is to our sun, scientists say it is probably as cold as Saturn. Known as a "super-Earth", the planet (designated Barnard's Star b, or GJ 699 b) is thought to be at least 3.3 times the mass of Earth and orbits its star once 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.

These questions could be answered by a future instrument that could take direct images of close-up planets, such as NASA's Wide Field Infrared Survey Telescope (WFIRST) telescope, which is slated to launch in the 2020s.

"Not one has ever been confirmed", he said in a Q&A published by the European Southern Observatory. "It is only by combining data and working collaboratively that this very challenging detection was possible". Over several decades, starting in the late 1930s, he studied the star, taking myriad images, and observing it moving against the background stars. The paper also says that there is no evidence of anything around the mass of Earth within the habitable zone of Barnard's Star-though Mars-mass objects haven't been ruled out.

Barnard's star is a red dwarf that is only six light years from our Solar System; only the three stars of the Centauri system are closer.

The new signal, on the other hand, seems to indicate something about 15 Earth-masses, which is unlikely to show a noticeable astrometric signal from Earth.

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In the middle of the last century, astronomer Peter van de Kamp was convinced Barnard's star was accompanied by two Jupiter-mass planets. Spotting planets at a huge distance is still important, and every new planet researchers are able to detect adds to our knowledge of the universe and nature itself, but majority are so distant that we'll likely never actually visit them. The research pushed the limits of the radial velocity detection technique, which becomes more hard the farther a planet is from its star.

However, as astrometry measurement techniques became more precise, scientists found that the supposed signals of Van de Kamp's two planets did not exist after all.

The exoplanet's sun, a tiny body known as Barnard's Star, is one of our solar system's nearest neighbors. This marks the first time the method has been used to find a planet orbiting so far out from its 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.

The magnitude of the wobble reveals the minimum mass of the planet that is responsible for the motion. One thing astronomers are confident about, though, is that this new planet is not habitable. That gave them enough data to detect the small signal of the planet. 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".

"He worked hard at improving the only technique at that time that had a prayer of finding planets, and spent decades collecting the data", Butler said.

"Difficult detections such as this one warrant confirmation by independent methods and research groups", Rodrigo Diaz, an astronomer at the University of Buenos Aires who was not involved in the research, wrote in a commentary for Nature. Barnard's Star provides the frigid planet only 2 per cent of the energy that the sun provides Earth.

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.

"It could be that a different explanation for the observational evidence we have will be found in the future", he said.

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