Vol. 528In section 1. Letters

Bayesian re-analysis of the radial velocities of Gliese 581. Evidence in favour of only four planetary companions

The nearby M dwarf Gliese 581 has been the focus of much attention. Since 2009, it has been known to host a system of four planets with masses between 16 and 1.9 times the mass of the Earth. One planet, Gl 581 d, is at the edge of the so-called habitable zone, and given the appropriate atmosphere and composition, it may contain liquid water at its surface. In 2010, Vogt et al. announced the discovery of two additional planets in the system. One of them, Gl 581 g, which is a 3.1 Earth mass planet in the middle of the habitable zone, the system made it into the headlines. M. Tuomi reanalyzes this discovery with a Bayesian statistical model finding, unfortunately, that the data does not support the existence of these two additional planets. Their existence is not ruled out, but the probability of their existence is insufficiently high to claim that it is a real signal as opposed to an artefact of the data spacing or pure noise. Additional observations of this intriguing system are needed.