We significantly constrain the sky position, distance, and mass of a possible additional, distant planet in the solar system by examining its influence on the distance between Earth and the Cassini Spacecraft. Our preferred region is approximately centered on (RA, Dec) = (40\arcdeg, −15\arcdeg), extending approximately 20 degrees in all directions.
@article{arxiv.1604.03180,
title = {Observational Constraints on Planet Nine: Cassini Range Observations},
author = {Matthew J. Holman and Matthew J. Payne},
journal= {arXiv preprint arXiv:1604.03180},
year = {2016}
}