NASA Astrobiology Institute Senior Scientist, David Morrison, answered a similar question on the Ask an Astrobiologist website (http://astrobiology.nasa.gov/ask-an-astrobiologist/): “Scientists don't know if we will ever be able to terraform Mars, but this is an interesting possibility to think about. Chris McKay of NASA Ames Research Center believes that it may eventually be possible to modify the atmosphere of Mars sufficiently to allow some genetically engineered plants to grow there in the open or in simple greenhouses. But if by terraforming you mean create temperatures as warm as on Earth and an oxygen atmosphere that we or other animals could breath, then McKay thinks this is impossible. Mars is just too small and too far from the Sun to sustain that much atmosphere.” Clearly, this effort would not be an easy task and there is not a current timeline for if or when it would take place. Some people also question whether it is a worthy goal. Given so many challenges and questions, there is no doubt that this topic will be up for considerable debate for a long time!