29 August 2000
A new study shows that life can not only survive beneath tons of ice at the dark, near-freezing junctions between glaciers and Earth, but actually thrive there. Researchers say the discovery reinforces the notion that the bottom of the ice cap at Mars' north pole should be a primary target in the search for life.
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July 6, 2000
The team's findings, published in Applied and Environmental Microbiology, the journal of the American Society for Microbiology, indicate that a population of active bacteria, some of which have DNA sequences that align closely with species in the genus Deinococcus, exists at the South Pole in the austral summer. A similar species lives elsewhere in Antarctica, but the discovery of microbes at the Pole may mean that the bacteria have become uniquely adapted to the extreme conditions there, including a scarcity of liquid water.
A species in the genus Deinococcus was first discovered in cans of irradiated meat in the 1950's, and is able to withstand extreme dryness and large doses of radiation. It is possible that the related bacteria from the South Pole may also possess these characteristics.
"While we expected to find some bacteria in the South Pole snow, we were surprised that they were metabolically active and synthesizing DNA and protein at local ambient temperatures of -12 to -17 Celsius (10.4 to 1.4 degrees Fahrenheit)," said Edward J. Carpenter, of the State University of New York at Stony Brook, who headed the research team. "Before attempting to publish the results, we wanted to be certain that the data were correct and were able to duplicate the observations in a second field season during January 2000."
Antarctica was once part of a supercontinent called Gondwanaland and drifted into its present position only about 60 million years ago. Deinococcus, however, is thought to be one of the earlier branches in the bacterial tree, and is much older than Antarctica in its present location. It is therefore unlikely that it evolved in Antarctica.
If the team's conclusions prove true, the discovery not only has important implications for the search for life in other extreme environments on Earth, but also for the possibility that life -- at least at the microscopic level -- may exist elsewhere in the solar system. Furthermore, the snow bacteria may possess unique enzymes and membranes able to cope with a subzero existence.
The team was careful to take samples at the edge of the clean-air sector at Amundsen-Scott South Pole Station to prevent contamination of the samples by bacteria from human habitation. The containers of bacteria were flown, still frozen, within 24 hours to the Albert P. Crary Science and Engineering Center at NSF's McMurdo Station for analysis. In examining the snowmelt, the researchers found coccoid and rod-shaped bacteria, some of which appeared to be dividing.
The findings by Carpenter and his colleagues, Senjie Lin, of the University of Connecticut, and Douglas Capone, of the University of Southern California, also may be significant because a separate team of NSF-supported investigators reported that ice cores taken at Lake Vostok, deep in the Antarctic interior, indicate the presence of microbes in what is suspected to be a vast pool of liquid water thousands of meters below the Antarctic ice sheet. That finding may have similar implications for extending the known limits of life.
NASA Space Science News for Dec. 10, 1999
Exotic microbes discovered near Lake Vostok: Scientists have uncovered a microbial world hidden deep beneath the frozen Antarctic ice that could help them learn more about how life can survive under extreme conditions on other planets or moons.
National Science Foundation
December 9, 1999
Bacteria May Thrive in Antarctic Lake
Two research teams, led by David M. Karl from the University of Hawaii and John C. Priscu of Montana State University, examined fragments of ice taken from roughly 3,600 meters (11,700 feet) below the surface -- about 120 meters (393 feet) above the interface of ice and suspected water. Both teams found bacteria in "accreted" ice, or ice believed to be refrozen lake water.
The teams conclude that a potentially large and diverse population of bacteria may be present in the lake. If so, this bacteria answers an intriguing scientific question about whether an extremely cold, dark environment which is cut off from a ready supply of nutrients can support life.
The DNA analysis by Priscu's team indicates that although the bacteria have been isolated for millions of years, they are biologically similar to known organisms. "Our research shows us that the microbial world has few limits on our planet," said Priscu. He added that Lake Vostok "is one of the last unexplored oases for life" on Earth.
The teams also conclude microbes could thrive in other, similarly hostile, places in the solar system. Lake Vostok is thought to be an analog to Europa, a frozen moon of Jupiter. Priscu notes in his paper that the Galileo spacecraft found evidence that liquid water exists under an icy crust on the Jovian moon. "Similar to ice above Lake Vostok, this ice may retain evidence for any life, if present, in the Europan ocean," he writes.
Evidence from radar mapping and other sources indicates that under several thousand meters of ice, liquid water may exist in Lake Vostok, possibly warmed by the pressure of the ice above or by thermal features below. The lake is roughly the size of Lake Ontario in North America. Vostok Station -- a Russian scientific outpost, which once recorded the lowest temperature on earth (-126.9 degrees Fahrenheit/ -89.9 degrees celsius) -- is located on the ice above the lake. As part of a joint U.S., French and Russian research project, Russian teams have drilled down into the ice covering the lake, producing the world's deepest ice core. Drilling was deliberately stopped to prevent introducing materials that would contaminate the water.
Karl notes at least one outstanding question about Lake Vostok: whether the ice in which the bacteria were found is sufficiently similar to the water in the lake to allow scientists to conclude that a similar population -- or even larger, more diverse one -- might thrive in the suspected liquid water.
Delegates from several nations, including a U.S. delegation sponsored by NSF, met in England last September to decide whether and how to explore the suspected lake without contaminating it. No firm proposal has yet been accepted to accomplish that. "We don't know what's in Lake Vostok, and we may never know, if we don't get the contamination issues solved," Karl said.
While the current findings may prove the existence of life in the lake, there are other scientific reasons to explore the lake itself. Ice cores have helped scientists assemble a climate record stretching back more than 400,000 years. Sediment samples from the bottom of Lake Vostok could extend that record to cover millions of years. "There are other, compelling reasons to go into the lake," Karl concluded.
NASA Ames Research Center, Moffett Field, CA
Dec. 9, 1999
Their findings are featured in a research paper co-authored by Dr. Chris McKay, a planetary scientist at NASA Ames Research Center, Moffett Field, CA, which will be published in the Dec. 10 issue of Science magazine. Co-authored by a multi-disciplinary science team, the research paper entitled "Geomicro-biology of Subglacial Ice Above Lake Vostok, Antarctica," analyzes the ice above Lake Vostok, a huge freshwater lake buried deep below the East Antarctic ice sheet.
"Microbes within the liquid water habitat of Lake Vostok may shed light on the viability of life in similar harsh environments beyond Earth, such as in the frozen ocean subsurface on Jupiter's moon, Europa, " McKay said. Galileo spacecraft results imply that a subsurface ocean could exist on Europa.
The research team tested samples from the ice 3,590 meters below Vostok Station, and found diverse colonies of microbes. Scientists say this is significant because the lake has been isolated from the usual sources of atmospheric-derived energy, such as photosynthesis, for millions of years.
"How the bacteria get energy (to survive) is an important question," McKay said. "The lake could be an analog to sub-ice Europa or subsurface Mars where conditions are similar."
Scientists believe ice is a good environment for primitive bacteria. The bacteria need less food because it's cold, and its metabolism slows down, somewhat like a hibernating bear's. Another finding was that DNA extracted from the microbes present in the team's Lake Vostok sample indicated the presence of only a few subgroups of known bacteria, coupled with low overall microbial diversity.
"It's what you'd expect, not teeming with rich life," McKay said. The team also found signs of bacterial life in the ice core and detected metabolic activity in some of the bacteria by measuring the bacteria's respiration rates during incubation.
Scientists said the sampled Vostok glacier ice also suggested that the lake water derived from a mixture of melted ice from both glacial and interglacial periods, deposited there approximately one million years ago.
Although the thickness of the ice on Europa is not known, scientists think that tidal forces could form cracks extending to the surface. Under the thin ice, conditions may be similar to the conditions at Lake Vostok. "If a similar ice layer is present under the surface of Europa's icy oceans, it may also harbor life," said McKay.
The research team included the paper's lead author, Dr. John Priscu, and others from the departments of Biology, Earth Science and Physics at Montana State University, Bozeman, MT. Other researchers were from the department of Geology, the University of Alabama, Tuscaloosa, AL and the U. S. Geological Survey, Reston, VA.
Montana State University
By Annette Trinity-Stevens
BOZEMAN -- When drilling through the ice of Antarctica's Lake Bonney in the 1980s, John Priscu and his team would utter expletives when reaching a depth of about six feet, or two meters.
On their way down to liquid water, which lay under a permanent ice layer about 15 feet deep, they invariably struck a layer of sediment.
"At first I cursed the sediment layer because it dulled the drill bits," recalled Priscu, a biologist at Montana State University-Bozeman who has done research in Antarctica for about 15 years.
Now he has kinder words for the pieces of sand and gravel entombed in the ice of Lake Bonney and several other lakes in the Antarctic Dry Valleys. That sediment layer, Priscu has learned, is alive. It supports a community of primitive microorganisms that know how to survive in an environment commonly associated with Popsicles.
Priscu, MSU civil engineer Ed Adams, postdoctoral student Chris Fritsen and six other scientists have written a paper on life in the Antarctic ice that appears June 26 in the journal Science. Days before the paper was to appear, Priscu, Fritsen and Adams were answering questions from reporters for the NBC Today Show, the BBC, Newsweek, the Washington Post, the New Scientist and several wire services.
Their work is analogous, Priscu and Fritsen said, to studies aimed at discovering life on Mars and Jupiter's moon Europa. Exobiology, or the search for life on other planets, is a hot topic now and is driving most of the public interest in discoveries like the one in Antarctica, the scientists said, although that focus is only a small part of their article.
Priscu admits it's hard to believe anything lives in the Antarctic Dry Valleys. It's a desiccated, rocky, desertlike landscape that looks like the surface of Mars except not as red. The air temperature is about that of a typical freezer.
"When [British explorer R.F.] Scott came walking down these valleys I'm sure he never thought there was something alive," Priscu said.
The key is liquid water. Adams figured out from trenching into the ice that the bits of gravel and sand in the sediment layer absorb sunlight during the Antarctic summer and create little pockets of water. The sediments, blown onto the lake by the wind and then buried, have bacteria and other microorganisms called cyanobacteria attached to them.
In the presence of liquid water and carbon dioxide from the surface, the cyanobacteria photosynthesize and produce organic carbon, which the bacteria use to make carbon dioxide for the cyanobacteria, and the cycle repeats itself.
"It's a lifecycle at the two meter level," said Adams. "It's a little ecosystem able to exist there."
What's more, this microbial community seems to make an ice-fixing substance -- like antifreeze -- that keeps the water pockets liquid for an extra two weeks before the onset of winter.
Fritsen said that's long enough for some of the microorganisms to reproduce. Some bacteria double every month, while others may take several years to double, he said.
"It's on the timeframe of lichens or cryptoendoliths -- the microalgae that grow inside rock in Antarctica because that's where the humidity is," he said. "It's very slow."
With three more years of funding from the National Science Foundation, the scientists plan to take a closer look at the lake's icy ecosystem.
"We want to know what organisms are doing well, how they do it, and how they can survive the freeze and thaw cycles in a liquid water environment," said Fritsen, who leaves soon for a faculty position at the University of Nevada at Reno. He'll take a portion of the new project, which he spearheaded, with him.
"We think we need to understand the interaction between organisms on our own planet to give us some signs of what to look for in other systems," Priscu said. "What we're saying is that for life on the edge you need a consortium of organisms to exist."
Other extreme environments where scientist have found life include hot vents along undersea trenches, deep in the earth's subsurface and in hot springs.
"Up to now people haven't looked in fresh water ice," Fritsen said. "They've looked in sea ice, and now scientists are talking about drilling into glaciers."
Priscu said the paper also says something about global climate change, which he studies in other projects.
"If this community reaches a steady state at two meters, then a change in meteorological activity will change the community," he said. "If it's too hot, the sediment will fall through the ice to the bottom. If it's too cold they won't get liquid water because there won't be enough radiant energy."
Sounds like now that he's stopped cursing the sediments and their family of microbes, he doesn't want to lose them.
Separate news releases issued by collaborating institutions are available at Oregon State University and at the University of North Carolina-Chapel Hill.