Abstract
Abstract The existence of a giant planet beyond Neptune—referred to as Planet Nine (P9)—has been inferred from the clustering of longitude of perihelion and pole position of distant eccentric Kuiper belt objects (KBOs). After updating calculations of observational biases, we find that the clustering remains significant at the 99.6% confidence level. We thus use these observations to determine orbital elements of P9. A suite of numerical simulations shows that the orbital distribution of the distant KBOs is strongly influenced by the mass and orbital elements of P9 and thus can be used to infer these parameters. Combining the biases with these numerical simulations, we calculate likelihood values for discrete set of P9 parameters, which we then use as input into a Gaussian-process emulator that allows a likelihood computation for arbitrary values of all parameters. We use this emulator in a Markov chain Monte Carlo analysis to estimate parameters of P9. We find a P9 mass of 6.2 − 1.3 + 2.2 Earth masses, semimajor axis of 380 − 80 + 140 au, inclination of 16 ± 5° and perihelion of 300 − 60 + 85 au. Using samples of the orbital elements and estimates of the radius and albedo of such a planet, we calculate the probability-distribution function of the on-sky position of Planet Nine and of its brightness. For many reasonable assumptions, Planet Nine is closer and brighter than initially expected, though the probability distribution includes a long tail to larger distances, and uncertainties in the radius and albedo of Planet Nine could yield fainter objects.
Highlights
Hints of the possibility of a massive planet well beyond the orbit of Neptune have been emerging for nearly twenty years
Trujillo & Sheppard (2014) noted that distant eccentric Kuiper belt objects (KBOs) with semimajor axis a > 150 au all appeared to come to perihelion approximately at the ecliptic and always traveling from north to south, a situation that they speculated could be caused by Kozai interactions with a giant planet, though detailed modeling found no planetary configuration that could explain the observations
We have presented the first estimate of Planet Nine’s mass and orbital elements using a full statistical treatment of the likelihood of detection of the 11 objects with 150 < a < 1000 au and q > 42 au as well as the observational biases associated with these detections
Summary
Hints of the possibility of a massive planet well beyond the orbit of Neptune have been emerging for nearly twenty years. Trujillo & Sheppard (2014) noted that distant eccentric KBOs with semimajor axis a > 150 au all appeared to come to perihelion approximately at the ecliptic and always traveling from north to south (that is, the argument of perihelion, ω, is clustered around zero), a situation that they speculated could be caused by Kozai interactions with a giant planet, though detailed modeling found no planetary configuration that could explain the observations. These disparate observations were unified with the realization by Batygin & Brown (2016) that distant eccentric. Combining the likelihood models from all of the simulations, we calculate probability density functions for all orbital parameters as well as their correlations, providing a map to aid in the search for Planet Nine
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
