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Chapter 14 : Life in Ice on Other Worlds

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Abstract:

All life on Earth represents a common genetic and biochemical system descendent from a common ancestor. The other worlds in our solar system that are the most promising targets in the search for life are Mars, Europa (a moon of Jupiter), and Enceladus (a moon of Saturn). Perchlorates are also metabolically active. It is known that microorganisms on Earth are capable of using perchlorates as electron acceptors, allowing anaerobic microbial respiration to occur where perchlorate replaces oxygen as the terminal electron acceptor. Studies of the microbes in the ground ice below dry permafrost in University Valley show that there is an adapted microbial community, and RNA data show that there is microbial activity. The availability of liquid water within the Martian subsurface (permafrost or regolith) would be concentrated into eutectic brines. As such, the microorganisms that could survive and potentially remain viable under such growth conditions would most likely be halophilic cryophiles. While the northern plains represent the most likely site of recent life due to the melting of near-surface ice, the southern highlands represent the best location to find long-frozen remains of ancient life on Mars. In the outer solar system there are two worlds that potentially have liquid water under layers of ice: Europa and Enceladus. In addition to Mars, Europa, and Enceladus, there are other worlds of interest to astrobiology-and they are also icy worlds.

Citation: McKay C, Mykytczuk N, Whyte L. 2012. Life in Ice on Other Worlds, p 290-304. In Miller R, Whyte L (ed), Polar Microbiology: Life in a Deep Freeze. ASM Press, Washington, DC. doi: 10.1128/9781555817183.ch14

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Image of FIGURE 1
FIGURE 1

Orbital variations and north polar insolation on Mars over the past 20 million years (Myr, million years). (Reprinted from Macmillan Publishers Ltd. [] [ ], copyright 2002.)

Citation: McKay C, Mykytczuk N, Whyte L. 2012. Life in Ice on Other Worlds, p 290-304. In Miller R, Whyte L (ed), Polar Microbiology: Life in a Deep Freeze. ASM Press, Washington, DC. doi: 10.1128/9781555817183.ch14
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Image of FIGURE 2
FIGURE 2

Subsurface ice at the Phoenix landing site on Mars, 68°N latitude. The flat areas visible at the bottom of the trench were hard, indicating the presence of ice-cemented ground, as expected. This material was spectrally identical to the soil. The lighter-colored, relatively softer ice seen was unexpected. Some of the light-colored ice exposed by digging has evaporated in the 4-sol (Martian day) interval, ruling out salt or carbonate as an alternative explanation to ice.

Citation: McKay C, Mykytczuk N, Whyte L. 2012. Life in Ice on Other Worlds, p 290-304. In Miller R, Whyte L (ed), Polar Microbiology: Life in a Deep Freeze. ASM Press, Washington, DC. doi: 10.1128/9781555817183.ch14
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Image of FIGURE 3
FIGURE 3

Water activity of a system in contact with ice as a function of temperature. (Based on vapor pressure data from .)

Citation: McKay C, Mykytczuk N, Whyte L. 2012. Life in Ice on Other Worlds, p 290-304. In Miller R, Whyte L (ed), Polar Microbiology: Life in a Deep Freeze. ASM Press, Washington, DC. doi: 10.1128/9781555817183.ch14
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Image of FIGURE 4
FIGURE 4

Scanning electron microscopy image of sp. nov. grown at –15°C. (a) Cells (single and diplococci) clustered in dense exopolysaccharide and semicrystalline aggregates. (b) Closeup of single cell adhered to the aggregate. Bars, 1.0 µm.

Citation: McKay C, Mykytczuk N, Whyte L. 2012. Life in Ice on Other Worlds, p 290-304. In Miller R, Whyte L (ed), Polar Microbiology: Life in a Deep Freeze. ASM Press, Washington, DC. doi: 10.1128/9781555817183.ch14
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