Our solar system contains 8 planets. However scientist think there is a another ice gaint WAAAAY far away from the sun in the Kuiper Belt. This planet is called Planet X or Planet 9. This planet could explain strange clustering of tans-Neptunian objects which are just objects beyond Neptunes orbit. he solar system. Its not Pluto.
Well we dont know the exact location of this mysteries Planet 9 but we do have a idea where it could possible be in the solar system. Planet 9 could be past Neptune and mabye in the Kuiper Belt. This Kuiper Belt is bunch frozen objects from orbit the sun. Its like a ring filled with icey objects. Scientist think thats where Planet 9 is located but where it is in the sky is unknown. The planet is so far away its hide to see. Some telescopes today could see this planet however scientist dont know where to look. The orbit of Planet 9 is estimated to be 20 times Neptunes distance from the sun. The orbit may tale 10,000 and 20,000 years to complete.
It is thought that Planet 9 use to be closer to the sun. It use to be after Saturn the 6th planet with rings. However due to gravity issues with other planets it was ejected to the outer solar system into the Kuiper Belt. Other theories say that Planet 9 is a rogue planet. This means Planet 9 was not created with the solar system. Planet 9 could of came from somewhere else in space that the suns gravity picked up.
Planet 9 is just a theory. This means its possible that planet 9 may not be there in the solar system. Scientist in the past had predicted planets not never was there. There is a chance Planet 9 is just another one of those planets. However scientist more evidence to prove planet 9. If Planet 9 is there then it could be a black hole. The black hole would not harm us though because of its distance. However as time goes by scientist keep finding good evidence for Planet 9. The chances of Planet 9 being in our solar sytem is pretty good.
NASA's article on this topic