Terraformed Mars, computer artwork. North is at top. Terraforming is the process of making another planet Earth-like so that it may be habitable by humans. The first stage of this process would involve raising the temperature so that water remains liquid. The temperature would have to be raised from today's average temperature of around -60 degrees Celsius. This could be done through an atmospheric greenhouse effect by using orbiting space mirrors to melt carbon dioxide ice at the Martian poles. The thicker atmosphere would trap heat and water could be released from underground deposits of ice. The planet could then be oxygenated by plants. Such a project would take centuries to complete.