A cold planet more than three times the mass of Earth may be orbiting a star in our neighbourhood, suggests a study of stellar movements published this week in Nature.
A red dwarf that predates the Solar System, Barnard’s star is the closest solitary star to the Sun. The star’s proximity to the Solar System has made it a long-running candidate in the hunt for exoplanets; however, none of the previous searches have led to a discovery.
Ignasi Ribas and colleagues analyse the data from two decades of radial-velocity measurements of Barnard’s star recorded by multiple facilities. The authors find a low-amplitude signal in the data that repeats every 233 days, which they suggest could indicate the presence of a super-Earth. Super-Earths are planets with masses larger than the Earth, but not as high as the Solar System’s ice giants, Neptune and Uranus. The candidate planet has a minimum mass of 3.2 Earths.
Furthermore, the authors conclude that the exoplanet orbits close to the so-called ‘snow line’ of Barnard’s star - the distance around a star at which it is cold enough that water can freeze onto pre-existing grains of material in a protoplanetary disk. It has been suggested that this region is favourable for planet formation.
The proximity of Barnard’s star to the Solar System, along with the relatively long orbit time of the candidate planet, makes the candidate exoplanet ideal for further examination, potentially offering new insights into planets beyond the Solar System.