Mars lacks sufficient carbon dioxide (CO2) to make terraforming a viable possibility with current technology, reports a Perspective published online this week in Nature Astronomy.

Terraforming is the hypothetical process of changing a planet’s conditions in order to make it habitable for Earth’s plants and animals, including humans. The most promising candidate for terraforming is our neighbouring planet, Mars. It has been proposed that the greenhouse gases stored in Mars’s rocks and polar ice caps could be released back into the atmosphere to make it thicker, heat the planet, and allow liquid water to remain on the surface.

Bruce Jakosky and Christopher Edwards focus on Mars’s available CO2, the only greenhouse gas present in sufficient quantities on the red planet to provide significant greenhouse warming. Using up-to-date knowledge provided by the rovers and spacecraft that have been monitoring Mars over the past 20 years, they identify all of the planet’s possible accessible surface and subsurface CO2 reservoirs, and their potential contributions to the atmosphere. The authors also take into account the continuous leaking of atmospheric CO2 into space.

At best, the authors conclude, the readily accessible CO2 could only triple Mars’s atmospheric pressure - a fiftieth of the change needed to make Mars habitable - and would increase the surface temperature by less than 10 °C. Terraforming Mars using the planet’s known CO2 will thus need technologies well beyond our current grasp.