Ares 9 or "Anarchy Planet"

Ares 9 is a Rim World planet where there are basically no rules. How did this come to pass? Well: the CHG doesn't acknowledge the planet as CHG property, despite having built the planet, as a means of making a puppet state where the business-owning relatives of government officials can operate with very few rules applying to them.

Then the puppet state collapsed due to numerous assassinations and poor management and now it's basically an anarchic wasteland where private companies destroy the planet with environmentally awful practices while being defended from the many madmen and psychopathic thrill-seekers who come to planet by mercenary armies. Basically it's purge night every night and during the day too and thanks to that this world is on its way to looking like something straight outta Mad Max.

The CHG government is having internal issues when it comes to what to do with the planet as many within it have financial interests in the world ("my son owning a company that operates there that would be stopped from the things it does has nothing to do with me wanting us to just leave it be") at the same time as a being so painfully obvious that the best thing to do in terms of humanity's success is to take over the planet and end the anarchy.

Geography

Originally, it was mostly swamps and jungles but many places have been turned into deserts by the activities of private companies and the many who come to the planet for the "no rules do whatever you like" experience - a large portion of whom are insane.

Fauna & Flora

Naturally, things would be pretty tame but the no-rules part has led to many bringing or just dropping lots of dangerous wild-life onto the planet that feed largely off of fast-reproducing rodents (also artificially introduced) and people. Plants are wildly varied and caught in a weird ecosystem-transition war of competing for resources.