Evidence for nine planets in the HD 10180 system

Aims. We re-analyse the HARPS radial velocities of HD 10180 and calculate the probabilities of models with differing numbers of periodic signals in the data. We test the significance of the seven signals, corresponding to seven exoplanets orbiting the star, in the Bayesian framework and perform comparisons of models with up to nine periodicities. Methods. We used posterior samplings and Bayesian model probabilities in our analyses together with suitable prior probability densities and prior model probabilities to extract all significant signals from the data and to receive reliable uncertainties for the orbital parameters of the six, possibly seven, known exoplanets in the system. Results. According to our results, there is evidence for up to nine planets orbiting HD 10180, which would make this star a record holder with more planets in its orbits than there are in the solar system. We revise the uncertainties of the previously reported six planets in the system, verify the existence of the seventh signal, and announce the detection of two additional statistically significant signals in the data. If these are of planetary origin, they would correspond to planets with minimum masses of 5.1-3.2+3.1 and 1.9-1.8+1.6 M⊕ on orbits with 67.55-0.88+0.68 and 9.655-0.072+0.022 day periods (denoted using the 99% credibility intervals), respectively