Terraforming is a theoretical process that would transform an inhospitable planet or moon into an Earth-like planet, complete with an atmosphere, water and plant life. Though many scientists believe that terraforming is possible, it remains an untested process as of 2015. It would take a massive amount of money, technology and work to terraform a planet, and a successful mission would represent a monumental achievement for humankind.
Scientists have different approaches to terraforming. Some envision encasing a planet in a type of shell, which would make it possible for humans to manipulate the planet's atmosphere and grow plants. No matter how it's done, the main goal of terraforming is to make a previously inhospitable place suitable for human life. Some experts argue that the technical challenges are too great to overcome. Others take issue with terraforming from an ethical standpoint, saying that it's not our right to take over and transform another planet.