Wait wait. I've read Sitchin and admire his work. Planet X was supposed to be a planet that aliens/god/Annunaki lived on, that collided with Earth, seeded it with life, and left the astroid belt in its wake. It was also supposed to, according to Sitchin, have an atmosphere filled with gold that was used to keep heat in. How does that fit with a comet?
How many planets are there now, including dwarf planets?
There are five official named dwarf planets, though expect more to come. There are like forty candidates that will probably get reclassified, and another 200 more bodies they are looking into.
So officially just five for now, Ceres (in the asteroid belt), Pluto, Makemake, Haumea, and Eris. Others will likely be Sedna, Orcus, Varuna, Quaoar, and a couple other unnamed bodies. Check wikipedia, Kuiper-belt bodies are the current 'rage' in astronomy right now so it stays pretty up to date and air-tight.
If anything Sedna is a better Planet X, its much bigger (over 1200 km diameter compared to 251). Both of these bodies are detectible only becuase they are so close to the sun in their odd orbit. Sedna swings waaaay far away, beyond where we can currently detect anything. It really makes you wonder how many of these objects are really out there.
Also, Sedna is thought to be the reddest object in the solar system.
...Then I ducked my head and the lights went out, and two guns blazed in the dark;
And a woman screamed, and the lights went up, and two men lay stiff and stark...
Planet X's main theory is some mass that is constantly disturbing the Kuiper Belt. Wouldn't surprise me one bit if they found also some dark matter out there orbiting causing the debris to become comets.
I know Eris is out there, but I don't think it has enough mass to account for all the anomalies.