Terraforming is a process of planetary engineering that transforms the environment of an uninhabitable world into one that is more suitable to humans and other Earth lifeforms.
By the year 2199, humanity had attempted to terraform only one other planet, Mars. Past settlers on Mars eventually succeeded in altering the planet's atmosphere enough to sustain a liquid water sea filling Amazonis Planitia. These efforts were interrupted in the 2180s by the devastation of the Second Inner Planet War. Sometime after the war, surviving settlers were evacuated to Earth, and terraforming work was abandoned. The Martian sea remained stable for some time afterward ("Messenger of Iscandar", "Farewell to the Solar System").
"Garmillasforming" is the name given to similar projects meant to support life from Garmillas. The Great Garmillas Empire pursues Garmillasforming activities across interstellar space as part of its territorial expansion. Large sections of Garmillas itself have been cut from the planet's crust and brought to distant star systems with vegetation, water, and other features intact, to serve as supply bases for transplanting life. A continent-sized piece of Garmillas was brought to Earth's solar system and suspended inside the atmosphere of Jupiter. As imperial forces launched planet bombs against Earth and wiped out its native ecology, plant species were selected from the floating continent and seeded on Earth as the first step in re-making it into a Garmillas-like world ("Messenger of Iscandar", "Escape from the Jupiter Sphere"). Partial Garmillasforming was also carried out on Pluto, where the empire established its primary base in the solar system, warming it enough for liquid water oceans to form underneath its icy surface ("The Trap on All Sides").
Planetary engineering can also be done to restore damaged environments. The Cosmo Reverse System, highly advanced technology from Iscandar, can draw on stored personal memories of life to rebuild an entire biosphere. One such device was used in late 2199 to terraform a dry and irradiated Earth following years of Garmillas attacks ("The Distant Promised Land", "Memories of the Blue Planet").