Maldek was a planet of this solar system, located between Mars and Jupiter. It was inhabited by a humanoid species. Just like the Apex-planet, Maldek was destroyed by nuclear war. The Asteroid Belt between Mars and Jupiter are the remains of Maldek.
There is another theory about the asteroid belt, and how it came into existence.
=> just a thought: Earth and the solar system are about 4,5 billion years old. Humanoid civilizations within this solar system are far more recent. (The furthest back some sources go, is 50 million years ago, which still leaves 4 billion years uncovered.) Maybe, Marduk could have split up in Earth and Maldek, and later on, Maldek self-destroyed.