Terraforming

Terraform is a word for the deliberate alteration of a planet's atmosphere and ecology to create an environment suited to human life. The word comes from the Latin word Terra, meaning Earth.

Examples of Terraforming
The Tenth Doctor used a terraform prototype to tidy up the sky of Earth from ATMOS poison in 2008. (DW: The Poison Sky)

Mitzi, the first cat to go into hyperspace, landed on the planet Photris, which was terraformed. (DWS: The Cat Came Back)

In late 25th century Planet Hollywood was terraformed by a consortium of entertainment businesses. (NSA: Peacemaker)

By the 26th century Mars had been completely terraformed by humans to make it habitable. They melted the icecaps and installed a gravity to make an Earth-like planet, albeit with less gravity and more UV light. (NA: GodEngine, BNA: Beige Planet Mars) The Monk tried to help the Ice Warriors revert the changes, but was unsuccessful. (BFA: The Resurrection of Mars)

Before the 40th century, Io was terraformed for use as the headquarters of the Galactic Federation. (NA: Legacy)

During the Second Great and Bountiful Human Empire, Agelaos was terraformed. (NSA: The Story of Martha: The Weeping)

In the 49th century Alfava Metraxis was terraformed. (DW: The Time of Angels)

The Source was a creation myth for the people on the planet Messaline. The Doctor, Donna Noble, Martha Jones and the Doctor's daughter Jenny discovered it was a terraforming device. The Doctor released the device to trigger the terraforming of Messaline in 6012. (DW: The Doctor's Daughter)

After Earth and Mars became uninhabitable, Pluto was terraformed by the Usurians. (DW: The Sun Makers)

Shanquis was terraformed using human technology. Even after the humans died out, the terraforming devices could be activated by spoken English. (CC: Bernice Summerfield and the Criminal Code)

Osphogus was terraformed. It was still inhabited five thousand years later. (BFA: The One Doctor)

The See-yee tried to terraform Earth, but the Doctor made the device malfuction so it produced a jungle. (AG: The Runaway Train)

Similar Processes
Technically, terraforming was the transformation of a planet to a more Earth-like form, but other species had similar processes to adapt planets to a form more like their own home planets.

Theoretical Monsters: A Credibility Test referenced the Kalekani, a species who used a terraforming virus which converted land into flat grassland, effectively turning it into a golfcourse. Fitz Kreiner believed they were made up. (EDA: Interference - Book One)

In 1864, the Cei sent a terraforming device to Earth so it could be used as an outpost. (BBCR: The Runaway Train)

In 1997, the Ice Warriors planned to wipe out the humans and terraform -- more specifically, areoform -- Earth, but they were unsuccessful. (NA: The Dying Days)

The Cthalctose created a terraforming device called the Genesis of Cthalctose. It sparked the Agent Yellow crisis in 2003. (NA: Eternity Weeps)

Torchwood Three speculated that the Vandrogonite Visualiser was intended as a terraforming device. (TWN: Pack Animals)

The Ice Warriors attempted to terraform Earth again in the early 21st century using a Martian fungus. (DW: The Seeds of Death)

In the 22nd century, the Daleks terraformed (or, technically, skaroformed) Antalin to resemble Skaro. (EDA: War of the Daleks)

The Daleks somehow terraformed Jupiter. The changed it from a gas giant to a planet that humans could survive on. (BFDE: Dalek War: Chapter Two, Dalek War: Chapter Three)

Terraforming Technology and Companies

 * Geo-forming was like terraforming, but much faster. (BFDE: The Survivors)
 * WorldCorp and PlanetScape were both human terraforming companies. (EDA: Dark Progeny)
 * Nooma was artificially created to test terraforming technology by the Aapex Corporation. (MA: Speed of Flight)
 * A Terran Federation ship carried terraforming equipment. The Sontarans took the ship and planned to use it to create cloning planets. (DWM: Pureblood)