I can answer this one with some authority.

No, the Egyptians only knew of the five visible planets (through Saturn.)

The "12th planet/Nibiru" comes from Zecharia Sitchin, one of the best promoters and WORST scholars around. He re-contextualized the Enamma Elish (the "genesis" of the Sumerians) to a truly bizarre story that goes like this:

The Annunaki (Sumerian Gods) were actually not gods but aliens from another planet (it gets lamer than that.) Humans are actually androids (yes, androids) that were built by these super-powerful aliens. The reason they came here to Earth was to mine the gold.

Why gold, you ask, when with their super-advanced technology they could create elements an even people? Well, gosh, Sitchin doesn't have a good answer for that, but that doesn't stop him. And, by the way, these super-advanced gods don't actually send machines to mine the gold... no, they create expensive and fragile androids (humans).

Apparently they also lost the recipe for making gold.

So, they live on the 12th planet of our solar system (described at different times as a "brown dwarf" or a planet)... and this planet is on a 3600 year orbit of the solar system and comes rocketing past Earth every so often, causing polar shifts -- the planet to roll over/the continents start skating around on the Earth like pancakes on a greased griddle -- rains of mana, magical days when the sun stands still, and the occasional tidal wave.

(I'm not making this up, folks. I could make up better than that.)

The fact that the Earth didn't undergo a cataclysm during 1600 BC (there were plenty of literate civilizations around) makes no difference to his theory.

And it gets sillier than that. He re-frames Inannas jewelry (in the trip to the underworld) to be strange technological things for controlling androids/etc.

"Nibiru" is one of the "throne names" given to Marduk after he defeats the primal goddess, Tiamat. It's the equivalent of "Mr. President" or "heavyweight champion of the world". There is one passage where the name occurs, and it's in the middle of a long string of titles given to Marduk that celebrate his victory.


It's been proven conclusively that he can't actually read the original texts.
There IS no brown dwarf (that's a small sun) with people living on it outside the orbit of Jupiter (we could see a star at that distance.)
The word he translates as "android" means "human"and not "artificial construct."
The Sumerian gods did not live on a planet.
The Sumerians didn't believe in UFOs or aliens.

The whole thing is actually a bit more complex and absurd than that. But it's earned him a lot of money.