While there have long been suggestions that their may be a mysterious Planet X at the outer reaches of our solar system, scientists and astronomers from the California Institute of Technology (Caltech) think that they have discovered indirect proof that it is there. By examining the deflections and perturbations in the orbits and trajectories of asteroids and other orbiting objects, astronomers including Michael Brown, whose previous work led to Pluto being downgraded to dwarf planet status, believe that a large object lies beyond the dwarf planet Pluto and the planet Neptune. A paper published by Brown and fellow astronomer Konstantin Batygin describes the evidence, suggests that the ninth major planet, which is too far and too dim to see, but which has ten times the gravitational pull of Earth, might be in a highly elliptical but distant orbit around the Sun. The paper suggests that it will have orbital period (the time of one full rotation around the Sun) of some 10 to 20 thousand years.
Post script: For those in the Northern hemisphere, during January and February 2016 there is a rare alignment of five brightest planets Mercury, Venus, Mars, Jupiter and Saturn, to be seen straddling the Moon in the morning sky. It is visible in the twilight of dawn viewing South East to South West from the UK and Western Europe.