How can we map masses orbiting the outer Solar System by determining the orbits of planets and smaller objects?
Iorio (Preliminary constraints on the location of Telisto/Planet Nine from planetary orbital dynamics) has suggested transmissions from the New Horizons probe (currently beyond Pluto) could be used to test for the influence of the proposed new planet, and provide constraints to its possible position.

It is estimated that the position of New Horizons could be affected by the proposed planet, of the order of 100 metres or more by 2019. It is stressed that this is a preliminary proposal:


  Moreover, the present investigation should be considered just as a preliminary sensitivity analysis which, by no means, is meant to replace a full covariance study based on extensive simulations of the ranging data from New Horizons and their reduction with accurate models including also PX itself, which is outside the scopes of this paper. Nonetheless, the possibility of using the telemetry of New Horizons seems appealing, and would deserve further, more detailed and dedicated studies which will, hopefully, prompted by the present one.