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.
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.