Microbial Life at Glacier Edges –Points to Possible Life Forms on Mars, Europa, Enceladus



Microbes living at the edges of Arctic ice sheets were methane is released could help researchers find evidence for similar microorganisms that could have evolved on Mars, the Jovian moon Europa, or Saturn's moon Enceladus. Ice sheets similar to thos on Earth exist elsewhere in the solar system, such as the buried water ice glaciers in the Hellas Basin region on Mars (image above). 

"If life was widespread during an early period on Mars when small lakes were common, we need to approach sampling with the expectation that pronounced variation in biological markers could occur even over distances as small as 100 meters (330 feet)," said Lisa Pratt, an astrobiologist and geomicrobiologist at Indiana University. 

"Mars is top priority right now because it's the easiest to get to," Pratt says. "We need to do a few things to make these missions more effective, however. We have to find a way to get deeper into the Martian subsurface. The surface is highly oxidized by Mars' atmosphere, which contains aggressive radicals. The surface also contains quite a bit of perchlorate, which 'scrubs' the surface of potential organic fossils. We need to get below this oxidized patina. We also need to find a way to drill into thick, dusty ice at the Martian polar caps to get to the layers that might tell us something about climate and climate change in the past."

"It is increasingly clear that on Earth, there are cold-adapted methanogenic microbes in Arctic, Antarctic and sea-bottom settings," said researcher Jeffrey White, an environmental biogeochemist at Indiana University. "Acetate fermentation is the principal pathway accounting for as much as 95 percent of methane production in these cold environments."

Methanogenic microbes rely on a community of microorganisms that provide the acetate and other simple molecules they consume. If such communities evolved in the cold corners of Earth, "it seems reasonable to search for evidence of similar biological processes on other icy bodies in our solar system," White said.

White and his colleagues recently went to Greenland as part of a $2.6 million NASA ASTEP grant. They investigated the western edge of the Greenland ice sheet, "one of the most readily accessible margins of a large ice sheet on Earth," White said. "The relatively manageable logistics and climate in Greenland compared to Antarctica made this area an excellent choice."

Current  data suggests that methane from microbial reactions is substantially richer in lighter isotopes at 20 to 40 parts per thousand than abiotic methane, explained Pratt. Small dissolved molecules or ions containing a lighter isotope move more rapidly at a given temperature than ones containing a heavy isotope. Consequently, those containing a light isotope interact more often with a bacterium's enzymes, and so get incorporated more often into what it makes, such as methane.

In 2011, the researchers used an infrared laser to look for methane at multiple sites across the valley that extends for tens of miles near the margin of the Greenland ice sheet. Measurements were taken about six feet (2 meters) above the soil surface for one to 4.5 hours each time.

Methane was spotted at several lakes and wetland areas. However, the methane levels seen were very close to what would be detected from normal atmospheric levels at ice margins in Greenland. Their next measurements will be taken at heights just above the soil surface to better distinguish local sources of emission.

Knowing how to look for life is one issue scientists are grappling with. Another is how to prevent Earth's own unique biological and non-biological materials from confounding studies or, worse, harming incipient life.

"Contamination is a big deal," Pratt says. "Scientists and engineers are working together to figure out how we can study Mars, even bring samples back to Earth, without causing any more harm."
More harm — because the people behind the Mars probe-landing Viking mission had not considered such things.

"Beyond Mars, there are many interesting places to explore," Pratt says. "My personal preference is (the Saturn moon) Enceladus. It has explosive plumes that we can fly a probe through without even landing it, which mostly takes care of the contamination issue. It is also believed there may be liquid water insulated below the moon's thick ice shell."

That's similar to Jupiter's moon Europa — but Europa lacks the plumes, which so conveniently eject material for orbiting probes to capture.

In the summer of 2013, the researchers intend to look for potential subsurface gaseous signs of life with an innovative drill they have developed. The device allows rapid transfer of unaltered gas samples from drilled boreholes directly into analytical instruments. A similar instrument could one day find use in planetary exploration, Pratt said.

The Daily Galaxy via Astrobio.net and newsinfo.iu.edu

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