1. Marduk is the name of one of the Sumerian, Babylonian and Assyrian Gods. He is the son of Enki, grandson of Anu. In Babylonian mythology he eventually became the supreme deity (after Anu, Enki and Enlil retired, and Ninurta, the son of Enlil was defeated).
2. Sumerian cosmogony tells the tale of a planet Marduk. Marduk, or Nibiru, supposedly is the name of the "twelfth planet" in our solar system. According to Sitchin's interpretation of the Sumerian creation tale, our solar system originally consisted of the Sun (Apsu) and nine planets. These were: Mercury (Mummu), Venus (Lahamu), Mars (Lahmu), Tiamat, Jupiter (Kishar), Saturn (Anshar), Pluto (Gaga), Uranus (Anu), and Neptune (Ea). Earth did not exist in those days, nor did the moon. Pluto was in between Saturn and Uranus. And there was a planet in between Mars and Jupiter, called Tiamat.
Then, a foreign celestial body, called Marduk, entered the solar system, clockwise, which is opposing the direction of the planets. The gravitational pull of Marduk changed the orbit of Pluto. The satellites of Marduk collided with Tiamat. Tiamat broke into two parts: one part was thrown in an orbit closer to the sun, in between Venus and Mars and became Earth. The other half was destroyed in the collision with other satellites and created the asteroid belt. Parts of the satellites became the meteors, that keep on having a clockwise orbit, unlike the planets and the asteroids, that go counter-clockwise. Through the gravitational pull of Tiamat, and after having been hit by minor satellites too, Kingu, Tiamat's moon, was thrown into another orbit too, and became Earth's moon.
Now Marduk didn't experience any collisions itself, but its orbit was changed. It was thrown into a major orbit around the Sun, clockwise, that takes about 3,600 years. Since then, Marduk got the name of Nibiru. It's (later) inhabitants, are called the Nefilim.
Since the first appearance of Marduk, our solar system consists of twelve bodies: the Sun, Mercury, Venus, Earth, the Moon, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto and Nibiru/Marduk. Hence the name, the twelfth planet for Nibiru/Marduk.
It is interesting to know that some astronomer-scientists actually believe such a planet exists. It would explain the apparent erratic behavior of some meteors, and it could also be an explanation for some of the cataclysms Earth has experienced.
Note that Earth's Galactic History mentions a planet called Maldek -which etymologically is akin to Marduk- in between Mars and Jupiter. According to Earth's Galactic History however, the humanoid civilization of that planet caused it to explode.
This topic was copied from the HyperBase and is likely to be revised.