Turning the Red Planet green? It's time to take terraforming Mars seriously, scientists say...

...the authors of the paper propose three phases of development.

First, scientists would use abiotic climate engineering techniques — such as deploying reflective solar sails, dispersing nanoparticles, or laying aerogel tiles — to warm the surface by at least 30 degrees Celsius (86 degrees Fahrenheit), enough to melt subsurface ice and release trapped carbon dioxide. This warming would thicken the Martian atmosphere and potentially support the presence of stable liquid water.

The second phase would introduce extremophile microbes — likely anaerobic and genetically engineered ones — capable of surviving in Mars' harsh conditions and kickstarting ecological succession. These organisms would begin producing oxygen and organic matter, slowly altering planetary chemistry.

The third and longest phase would focus on building a complex biosphere, increasing atmospheric pressure and oxygen content to eventually support more advanced plant life, and, in the very long term, potentially allow humans to breathe unassisted.