Terraforming Mars. Artwork of the first phase of terraforming Mars (making it Earth-like). This would involve raising the temperature so that water (in the craters) 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 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.