New constraints on the location of P9 obtained with the INPOP19a planetary ephemeris

Abstract

Context.We used the new released INPOP19a planetary ephemerides benefiting from Jupiter-updated positions by theJunomission and reanalyzedCassiniobservations.Aims.We test possible locations of the unknown planet P9. To do this, we used the perturbations it produces on the orbits of the outer planets, more specifically, on the orbit of Saturn.Methods.Two statistical criteria were used to identify possible acceptable locations of P9 according to (i) the difference in planetary positions when P9 is included compared with the propagated covariance matrix, and (ii) theχ2likelihood of postfit residuals for ephemerides when P9 is included.Results.No significant improvement of the residuals was found for any of the simulated locations, but we provide zones that induce a significant degradation of the ephemerides.Conclusions.Based on the INPOP19a planetary ephemerides, we demonstrate that if P9 exists, it cannot be closer than 500 AU with a 5M⊕and no closer than 650 AU with a 10M⊕. We also show that there is no clear zone that would indicate the positive existence of planet P9, but there are zones for which the existence of P9 is compatible with the 3σaccuracy of the INPOP planetary ephemerides.