Free Astronomy Magazine September-October 2018

40 SEPTEMBER-OCTOBER 2018 PLANETOLOGY The scientific literature, once again, suggests a possible solution: trans- forming Mars from an inhospitable world in- to a habitable planet through a series of in- terventions whose aim is to regenerate the Martian atmosphere, creating a greenhouse effect capable of rais- ing the average tem- perature to the surface and re-establishing the ancient water cycle. The first explicit ref- erence to this fanci- ful transformation ap- peared in 1942 in a story by Jack Williamson, published in As- tounding Science-Fiction. It was on that oc- casion that the author used for the first time the term “terraform” (which became a verb in the 90s), which is the process of trans- forming an unlivable planet into an Earth, with all of the environmental conditions and affinities of our home world. What seemed like only a bizarre utopia in 1942 became within a few decades a topic of discussion among scientists. In the 1970s, thanks also to the futuristic vision of Carl Sagan, NASA pro- moted a feasibility study for terraform- ing Mars. The scien- tists and engineers involved in the study came to the surprising conclusion that it was possible to make that planet habitable. Since the end of the seventies, many scien- tific articles have been produced on terra- forming Mars, which have proposed differ- ent ways to achieve substantially the same final scenario. The terraforming of Mars is an ever-grow- ing topic of discus- sion, with the real difficulties needed to be to overcome to start the process ever- P hotomontage made from im- ages from Nature Communications showing Mars in its current ap- pearance − red and arid − to the left, in contrast to the same land- scape covered with water more than three billion years ago. [Na- ture Publishing Group/ AFP/Ar- chives/Jon Wade, James Moore] B illions of years ago, when the Red Planet was young, it appears to have had a thick atmosphere that kept temperatures warm enough to support surface oceans of liquid water − a critical ingredient for life. The animation shows how the surface of Mars might have appeared during this ancient clement period, beginning with a flyover of a Martian lake. The artist's con- cept is based on evidence that Mars was once very different. Rapidly moving clouds suggest the passage of time, and the shift from a warm-and-wet to a cold-and-dry climate is shown as the animation progresses. The lakes dry up, while the atmosphere gradually transitions from Earthlike blue skies to the dusty pink and tan hues seen on Mars today. [Michael Lentz, GSFC/NASA]