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

¹ GéoAzur, CNRS, Observatoire de la Côte d’Azur, Université Côte d’Azur, 250 Av. A. Einstein, Valbonne 06560, France
e-mail: agnes.fienga@geoazur.unice.fr
² IMCCE, Observatoire de Paris, PSL University, CNRS, Sorbonne Université, 77 Avenue Denfert-Rochereau, Paris 75014, France
³ Dipartimento di Ingegneria Meccanica e Aerospaziale, Sapienza Universitä di Roma, Via Eudossiana 18, Rome 00184, Italy

Received: 10 March 2020
Accepted: 27 May 2020

Abstract

Context. We used the new released INPOP19a planetary ephemerides benefiting from Jupiter-updated positions by the Juno mission and reanalyzed Cassini observations.

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) the χ² likelihood 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 5 M_⊕ and no closer than 650 AU with a 10 M_⊕. 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 3σ accuracy of the INPOP planetary ephemerides.