In January scientists presented the latest evidence for the existence of a ninth 'real' planet in our solar system. The evidence was based on unexpected behaviour by a number of Kuiper Belt Objects (generally small asteroids orbiting beyond Neptune, 15k to 25k light seconds from the sun). Based on orbital perturbations and clustering it appears that there may be a much larger object within the belt, perhaps a large and distant ninth planet.
Recently another group has presented further evidence for Planet IX based on tiny irregularities in the orbit of the Cassini spacecraft. From this data it is postulated that IX is between 4 and 10 Earth masses, and orbits around 300,000 light seconds (600 AU) from the sun. Such a planet could be a rocky terrestrial type. It's hoped that the Dark Energy Survey, a southern hemisphere cosmology project, may discover more data.