Following the recent unveiling of evidence that there is an object in the outer reaches of the solar system large enough to affect the orbits of known planetoids, researchers have started looking for more clues as to where the elusive Planet Nine might be found. One of these new investigations was conducted by Matthew J. Holman and Matthew J. Payne of the Harvard-Smithsonian Center for Astrophysics, using data on the position of the Cassini space probe orbiting Saturn. They used that positioning data to look for purbutations in the probe’s orbit to look for the potential influence of an unaccounted-for large gravitational body.
They indeed found the anomalies they were looking for: "we put Planet Nine at a whole different slew of locations – all different possibilities on the sky, different distances, different masses – and tried to find out whether that constrains things even more," according to Payne.
They were able to narrow down what they believe to be the most likely position for Planet Nine, in an area of sky in the constellation Cetus, close to Aires and Pisces, somewhere in a 20-degree arc centering on a position at 40º right-ascension, -15º declination.
Their idea to use the Cassini probe’s positional data came from a paper published earlier this year by researchers at the Côte d’Azur Observatory in France, who proposed the idea that these clues could be drawn from observations of Cassini’s orbits, provided the craft were to continue operating until 2020. Unfortunately, NASA reports that Cassini’s mission is due to conclude next year, since it is nearly out of fuel, now that it is twelve years into a twice-extended four-year mission.
Of course, this does not mean that the search for Planet Nine is ending, as there are other avenues of research to follow, including looking for indirect gravitational evidence on other objects in the solar system, and if all goes well, actual direct imaging of the planet through the next generation of powerful telescopes.