Planet X  - a Brown Dwarf

    This tenth planet called Nibiru is what is called a “brown dwarf.” Often portrayed as “failed stars,” brown dwarves are bigger than giant planets like Jupiter, but their individual masses are less than 8 percent of the sun’s mass so they can’t shine like a star. Brown dwarves are best viewed in the infrared because surface heat is released as they slowly contract. That’s why the infrared astronomical satellite IRAS  is able to find these things so well. Want to see a comparison of just how big a brown dwarf is?  See below  for a photo. Note that it’s enormous, much bigger than anything we have in our solar system. Think . . . elephant and mouse . . . Planet X and Earth.
   Astronomers have found many types of objects in orbit around stars. These range from other full-sized stars like our sun (binary star systems) to Jupiter sized planets (never directly imaged but inferred from radial-velocity spectroscopy). The relative sizes of these various types of bodies are shown above for comparison. Even though a brown dwarf can be similar in diameter to a Jupiter sized planet, brown dwarfs are 13-75 times more massive and they can appear on the order of 100-1,000,000 times brighter than a Jupiter sized planet at infrared wavelengths where they are studied with telescopes.

Credit: Gemini Observatory/Artwork by Jon Lomberg
see  for more information on Brown Dwarves.