  We use an extensive suite of numerical simulations to constrain the mass and
orbit of Planet Nine, the recently proposed perturber in a distant eccentric
orbit in the outer solar system. We compare our simulations to the observed
population of aligned eccentric high semimajor axis Kuiper belt objects and
determine which simulation parameters are statistically compatible with the
observations. We find that only a narrow range of orbital elements can
reproduce the observations. In particular, the combination of semimajor axis,
eccentricity, and mass of Planet Nine strongly dictates the semimajor axis
range of the orbital confinement of the distant eccentric Kuiper belt objects.
Allowed orbits, which confine Kuiper belt objects with semimajor axis beyond
380~AU, have perihelia roughly between 150 and 350~AU, semimajor axes between
380 and 980~AU, and masses between 5 and 20 Earth masses. Orbitally confined
objects also generally have orbital planes similar to that of the planet,
suggesting that the planet is inclined approximately 30~degrees to the
ecliptic. We compare the allowed orbital positions and estimated brightness of
Planet Nine to previous and ongoing surveys which would be sensitive to the
planet's detection and use these surveys to rule out approximately two-thirds
of the planet's orbit. Planet Nine is likely near aphelion with an approximate
brightness of $22<V<25$. At opposition, its motion, mainly due to parallax, can
easily be detected within 24 hours.
