The vast majority of habitable worlds require some degree of terraforming to make them safe for humans. The primary concern is nullifying any dangerous viruses, bacteria and potential allergens. Making the planet comfortable (eg: climate modification) is a secondary concern. Planets that don't fit certain basic criteria (sun, water, soil, gravity, temperature etc.) are considered uninhabitable until terraforming technology improves further.
Planets that don't require terraforming at all are extremely rare and are called "paradise worlds". Most of the earliest planets to be colonised were paradise worlds, and have become the capitals of the nations that grew around them. |
