An international team of researchers have discovered a cold super-Earth exoplanet orbiting around the red dwarf Barnard — the second closest star system to Earth. The new planet candidate, called Barnard’s star b (or GJ 699 b), is a super-Earth with a minimum of 3.2 Earth masses. It orbits its red star every 233 days near the snow-line, a distance where water freezes. Lacking atmosphere, its temperature is likely to be about minus 170 degrees Celsius, which makes it unlikely that the planet can sustain liquid water on the surface.
“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 lead author Ignasi Ribas, researcher at the Spanish National Research Council (CSIC). “However, we must remain cautious and collect more data to nail the case in the future, because natural variations of the stellar brightness resulting from starspots can produce similar effects to the ones detected,” Ribas added.
The results of the study are published in the journal Nature. Barnard’s star, which is just six light-years away, moves in Earth’s night sky faster than any other star. It is smaller and older than our Sun and is among the least active red dwarfs known, so it represents an ideal target to search for exoplanets.
Astronomers have since 1997 collected a large number of measurements on the oscillation movement of the star. In 2015, they found that it could be caused by a planet with an orbital period of about 230 days. To confirm the hypothesis, the team used the radial velocity method.
“With the radial velocity method, precision spectrometers are used to measure the Doppler effect. When an object moves away from us, the light we observe becomes slightly less energetic and redder. On the contrary, when the star approaches us, the light becomes more energetic and bluish,” Ribas said. “When we re-analysed all the combined measurements, a clear signal arose at a period of 233 days. This signal implies that the Barnard´s star approaches and moves away from us at about 1.2 meters per second – approximately the walking speed of a person – and it is best explained by a planet orbiting it.”