Conclusions

Although the Viking mission found no evidence of life on the Martian surface (reviewed by [60, 73]) the search for extant and extinct life on Mars continues. There is mounting evidence from missions to Mars that there was liquid water on the surface of the planet early in its history [e.g. 70]. Additionally, there may be occasional liquid water on the surface today resulting from melting snow fields [15]. Further, data from recent missions suggest that evaporites exist on Mars [10, 18, 27, 97].

Halophily/osmophily is not rare and probably evolves easily, and arose many times. If life evolved on Mars, then osmophily probably evolved as well. Osmophiles are best suited for life in brines and evaporites. As discussed previously, halophiles/osmophiles are found in a variety of cold environments. Studies have shown that microbes can metabolize in permafrost [94]. Halophiles/osmophiles are better adapted than other organisms to survive in brines, drying and freeze-thaw cycles, as may have occurred on Mars.

The last vestiges of an extinct Martian biota, or an extant biota could be present in a cold, desiccating environment, perhaps in brine pockets within permafrost. Therefore, it is possible that the last organisms to survive on the Martian surface were osmophiles, and that any near surface extant life on Mars may be osmophiles.

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