Mexis was a moon of Irk.
At some unknown period in the distant past, the Iconians deployed one of their Gateways on this moon where it remained undetected for hundreds of years. For many years, the Irkens used the molten core of Mexis to provide the Irken Empire with energy. The Irkens were noted as one of the first peoples to test such a procedure and their work was duplicated by the Vortians who tapped their moon of Jerado to provide a similar source of energy for Vort.
In 4493 over-mining and insufficient safety precautions led to the almost-destruction of Mexis.
The devastation also opened a political rift within the Irken Republic, half of the Imperial Senate favored a typical Irken response of striking out to take whatever they needed to recover from the disaster. However the other half, led by the Tallest, ZIM, suggested requesting aid from the Conglomerate to help the Republic repair the damage. The senate finally decided in favor of ZIM's plans and opened peace talks with the Conglomerate.
The almost-destruction of the moon almost destroyed the Iconian Gateway within it leaving remnants of the ancient device that would remain undetected until 4496.