Whether you call it Planet X or Planet Nine, talk of another planet lurking in our Solar system won't go away. So what does the discovery of a new object – nicknamed "The Goblin" – add to the debate?
Discovery of many icy worlds helps unravel the solar system's history.
It turns out that a common physical process called diffusion can explain the orbits of faraway minor planets – no need for a Planet Nine.
Why Planet Nine should be found in the next few years ... if it exists.
The search for new objects, including new planets, in our solar system has turned up some interesting finds. There have been a few failures over the years too.