Terraforming is the process of altering a planet to make it more suitable for life (habitable). Usually this means making the planet suitable for most, if not all, Earth life. However, if there is dormant or hidden life on the planet, terraforming will change conditions so that this life can possibly flourish. In terraforming, there are intermediate stages where the planet has become habitable, but only to organisms that can survive in extreme environments.

Until recently, the topic of terraforming Mars was considered more the subject of science fiction novels rather than serious scientific discussion. But it is now known that we can change the climate of a planet, as we are inadvertently doing it on Earth. In addition, it is thought that billions of years ago Mars did have a climate suitable for life. The main focus of current scientific studies of terraforming is the restoration of...