Micro

Planet Micro is the home world of the Micromasters. Unlike other planets that Transformers tend to set up residence on, it's actually quite a nice place to live by galactic standards, possessing a breathable atmosphere, and plenty of greenery and natural water sources around which the planet's cities are built. Micro's cities are especially technologically advanced, with one third of the planet's power being supplied by an experimental plasma energy plant. The planet is lit by twin suns, and orbited by four moons, one of which is covered in lakes of magma and is home to the Satellite Penitentiary, a maximum security prison facility.

After a military reinforcement program, Micro was outfitted with extensive defense systems and become known as planet Zone.

Victory cartoon
Seeking to acquire a large personal stockpile of energy for himself, the duplicitous Decepticon Breastforce member Hellbat hired the Crossformers, Blue Bacchus and Black Shadow, to help him attack Micro and raid the planet's numerous energy sources. Although the planet was located in the region of space under the protection of God Ginrai's arm of the Space Defense Force, he was occupied in G Nebula 89, necessitating the intervention of Star Saber and his Earth-based Autobots. Star Saber arrived with Jean Minakaze and Micro natives the Rescue Team, who went off to do some sightseeing while Star Saber investigated the attacked areas with planetary official Governor Raikuru.

That evening, Hellbat and the Crossformers attacked the plasma energy plant, and Star Saber sprang into action, backed up by the samurai warrior Greatshot. Although they were able to repel the villains, some parting fire from Hellbat began a chain reaction that would destroy the plasma energy plant, forcing Star Saber to risk his life tearing it free of the planet and hurling it into space.

Hellbat, it soon transpired, had not come to Micro alone. The rest of the Breastforce was also on the planet, having arrived to liberate their comrade Gaihawk from imprisonment in the Satellite Penitentiary. Setting the prison adrift in a lava sea, the villains were able to free their teammate despite resistance from Star Saber, and even the prison itself was lost beneath the molten rock.[http://transformers.wikia.com/wiki/Rescue!_Gaihawk Rescue! Gaihawk]  With the addition of Gaihawk to their ranks, the Breastforce were now able to combine into the giant robot Liokaiser, and bested Star Saber in a fraught battle. With this victory, the Decepticon departed planet Micro, and, with God Ginrai having returned, Star Saber's Autobots pursued them back to Earth.

Zone story pages
The development of the new super-fuel Energon Z on Micro prompted an extensive military reinforcement of the planet, in order to protect this new power source from the Decepticons. Employing a process developed by the Super Car Patrol Team, the Transformer space pioneers known as the Powered Masters rebuilt Micro, converting its surface into a technological sprawl and outfitting the planet with the Zone Base, a massive defense base comprised of interlocking installations manned by numerous Micromaster teams. In honor of this, the refurbished planet became known as "Zone".

Zone OVA/manga
When the planet Feminia was destroyed by the Nine Great Demon Generals (resulting in the disappearance of Star Saber) two of its surviving inhabitants, Cain and Emusa, were brought to Zone by the Micromasters. Having hailed from a lush natural world, Emusa didn't particularly feel at home on the machine world of Zone, but his concerns were shelved when several of the Demon Generals attacked the planet and stole the Energon Z. While a contingent of Micromasters gave chase to Earth, Powered Masters Dai Atlas and Sonic Bomber arrived on Zone with the injured Star Saber, who they had recovered and brought to the planet for medical attention. Dai Atlas and Sonic Bomber subsequently headed to Earth and defeated the Decepticons, and when they returned to Zone, a ceremony was held appointing Dai Atlas the new Supreme Commander of the Autobots. [http://transformers.wikia.com/wiki/Enter_the_New_Supreme_Commander,_Dai_Atlas! Enter the New Supreme Commander, Dai Atlas!]

The AllSpark Almanac
Zone, formerly known as Micro, was a robotic planet in the Autobot Commonwealth.

Transformers: Unicron Trilogy
Micro, also known as Zone, is the home world of the Micromasters in the Milky Way Galaxy in Transformers: Unicron Trilogy. Micro appeared considerably smaller than the planet Earth and the size of Mercury.