Barnard's Star b, also known as GJ 699 b, was a super-Earth extra solar ice planet candidate proposed to be orbiting the very-low-mass red dwarf star Barnard's Star 6 light years away from Earth in the constellation of Ophiuchus. It was discovered by an international team of astronomers, including the European Southern Observatory, and Carnegie Institution for Science, and was announced through the Nature journal on November 14, 2018.
More recent studies conducted in 2021 and 2022 concluded the radial velocity signal corresponding to Barnard's Star b is most likely an artifact of stellar activity; and thus probably does not exist.
Characteristics[]
Barnard's Star b has not actually been confirmed and still remains a candidate, with a confidence figure of 99%. The research team that made the announcement will continue observations to ensure that no improbable variations in brightness and motion in the star might account for the discovery. Direct imaging opportunities of the planet from large ground-based telescopes (or potentially, the W FIRST telescope) are expected within the next ten years (as of 2018). There is an outside chance that a transit of the star might also allow for imaging.
The planet was discovered through the radial velocity method, the most common planet-hunting technique. A "wobble" observed in Barnard's Star's motion was confirmed to have a period of about 233 days, corresponding to a semi-major axis of 0.4 AU. The mass of the likely planetary body was then deduced to be about 3.2 Earth mass. Analysis was careful and extensive. Lead astronomer Ignasi Ribas notes that "we used observations from seven different instruments, spanning 20 years of measurements, making this one of the largest and most extensive data sets ever used for precise radial-velocity studies.". The planet has a radius of about 1.2-1.3 Earth radii.
Barnard's Star b is expected to be freezing cold, with an equilibrium temperature of about 105 K (-168 °C; -270 °F). While it orbits very close to its star by Solar System standards (orbiting slightly further than Mercury does to the Sun), is around the snow line for a dim red dwarf star like Barnard's Star. This is the point were volatile compounds such as water condense to form ice and thus outside the assumed habitable zone where temperatures are right for surficial liquid water. In addition, Barnard's Star also has very large and powerful flares which causes its temperatures to soar from 3,100 kelvins to around 8,000 kelvin. These flares likely contain hefy amounts of X-ray radiation and it is not clear whether or not Barnard's Star b has a sufficient atmosphere to protect any life forms from this.
Astronomers expect to find more such "snow line" planets as proto-planetary accretion is favorable in this temperature range. A second planetary companion for Barnard's Star has been suggested based on unconfirmed "wobbles" in the current system.