Abstract
Although the martian environment is currently cold and dry, geomorphological features on the surface of the planet indicate relatively recent (<4 My) freeze/thaw episodes. Additionally, the recent detections of near-subsurface ice as well as hydrated salts within recurring slope lineae suggest potentially habitable micro-environments within the martian subsurface. On Earth, microbial communities are often active at sub-freezing temperatures within permafrost, especially within the active layer, which experiences large ranges in temperature. With warming global temperatures, the effect of thawing permafrost communities on the release of greenhouse gases such as carbon dioxide and methane becomes increasingly important. Studies examining the community structure and activity of microbial permafrost communities on Earth can also be related to martian permafrost environments, should life have developed on the planet. Here, two non-psychrophilic methanogens, Methanobacterium formicicum and Methanothermobacter wolfeii, were tested for their ability to survive long-term (~4 year) exposure to freeze/thaw cycles varying in both temperature and duration, with implications both for climate change on Earth and possible life on Mars.
Highlights
On Earth, permafrost is defined by temperature and refers to any rocks, soil, or sediments that remain at or below 0 ◦C for at least two years in a row [1,2]
(17%) after 22 days corresponds to the culture that showed no methane production (0%) after 7 days’ incubation at room temperature
The experiments described here subjected a mesophilic and a thermophilic methanogen to long-term exposure (~4 year) to extreme temperature changes varying in duration
Summary
On Earth, permafrost is defined by temperature and refers to any rocks, soil, or sediments that remain at or below 0 ◦C for at least two years in a row [1,2]. On Mars, temperatures vary widely over one sol, often ranging between just above freezing during the day to below −100 ◦C at night [3], constituting rapid freeze/thaw cycles. Gallagher et al [5] conclude that high-latitude periglacial landforms are “evidence of the protracted, widespread action of thaw liquids on and within the martian surface” occurring within the last few million years. The authors propose that perchlorate salts, detected by the Phoenix lander, contribute to martian freeze/thaw cycles, resulting in the periglacial geomorphology of the planet [5]. Johnsson et al [6] contend that geomorphological features provide evidence for freeze/thaw activity within the last few million years on Mars and suggest that the planet may have a more widespread and cyclic freeze/thaw process than previously thought
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