By Girvan McKay
This is a strange story which begins in Antarctica and continues on a distant satellite of Jupiter.
Antarctica is one of the driest and coldest places on Earth. For this reason it is regarded by scientists as a laboratory for the study of the inhospitable conditions on the outer planets of our solar system. Antarctica has come to be known as "the closest thing to Mars". However, recent discoveries suggest that it might have lessons for us about the possibilities of some form of life on (or rather, in) Europa, one of the satellites of Jupiter. This may seem far-fetched, so some explanation is needed for this statement.
In eastern Antarctica there's a scientific base maintained by the Russians. It's known as Vostok, which means "East" in Russian. The base is situated in an area that's mainly hilly, but a large part of it flattens out to form a very long but relatively narrow expanse, as smooth as a mirror. It struck the Russians that its shape and surface was exactly like the lakes in Russia when they freeze over in winter. By using radar and artificially generated seismic waves, they discovered that underneath them was a vast warm water lake which has since been given the name Lake Vostok. It lies under nearly 4 kilometres of solid ice (about 2 and a half miles) but is warm enough to remain liquid - and this is in one of the coldest places on Earth! It's been suggested that geothermal heat from radioactive decay in the Earth's interior has kept it from freezing. This heat may radiate from warm rocks in the bottom of the lake. At the same time, sheet ice may act as a blanket protecting it from the Antarctic air.
Lake Vostok is 250 kms long by 40 wide and 400 metres deep - approximately the size of Lake Ontario or half the size of Wales, making it one of the 10 biggest deep water lakes in the world. Its long and narrow shape is very similar to that of lakes that have formed in earthquake faults in other parts of the world. Since the discovery of Lake Vostok, 70 other subglacial lakes have been detected in Antarctica.
More Information on "Lake Vostok" "Satellite-borne radar detected a flatness in the surface of the ice sheet around the Vostok station. This finding shows the ice sheet is floating on water. When the ice sits on top of rock, the terrain is uneven, often hilly or mountainous." Under four kilometres of ice, Lake Vostok is immense in size, covering an area of 14,000 km2 and reaching a depth of 500m. Promising to be the cleanest, purest lake on Earth, it could possess a unique habitat for ancient bacteria with an isolated microbial gene pool characteristics developed perhaps 500,000 years ago."
A huge rig has drilled down almost to the top of the lake and the ice cores obtained from the drilling have been found to contain bacteria. However, the Russians have stopped short of drilling right down to the water of the lake for fear of contaminating it. Kerosene is used as a lubricant for the drill bits and if this got into the lake it would seriously prejudice the research results. At present studies are being carried out to see if hot water could be used as a lubricant instead of kerosene. This would freeze behind the drill bit and seal the hole, thus protecting the lake from contamination. That anyway is the theory but it hasn't been proved yet whether it'll work. (There have been appeals not to carry out further drilling for fear of such contamination. This seems to be a clash between the interests of astronomers and those of environmentalists.)
It may seem strange that a sub glacial lake (a lake under the ice) in Antarctica could teach us anything about conditions on Europa, but that is what astronomers are suggesting. Detailed observations of Europa were carried out during the Galileo Orbiter's mission and various flybys. This satellite has been described as the most intriguing of Jupiter's moons. Images of its surface show a texture very similar to that of ice rafts in Earth's Polar Regions, indicating that under the ice is an ocean covering the entire satellite. This and the findings at Lake Vostok suggest that maybe oceanic life could exist on Europa.
Ice samples from cores drilled close to the top of the lake have been analysed to be as old as 420,000 years, suggesting that the lake has been sealed under the icecap for somewhere between 500,000 and more than a million years. Biologists suspect that there may be life forms that have been unaffected by surface conditions for up to a million year, making Lake Vostok an invaluable, living biological museum. Geologists tell us that Antarctica was once warm enough for plant and animal life. Since the continent froze over the lake has been completely sealed off from the outer atmosphere and from the light of the sun. Not a single photon of light has reached the lake in all the long period that it has been frozen over. If life in the form of bacteria or whatever can survive in such conditions, it may be that it also exists in the ice-covered ocean of Europa.
At the Jet Propulsion Laboratory, which manages the Galileo Mission, a project has been initiated to probe the waters of Lake Vostok for life - a model for a possible mission to Europa. The "Europa/Vostok Initiative" is developing a probe design that could melt through the ice and deploy a submersible to explore a liquid body of water beneath. The concept starts with a melter probe- the so-called "cryobot" - which melts down through the ice over Lake Vostok, unspooling a communications and power cable as it goes. The cryobot carries with it a small submersible, called a "hydrobot," which is deployed when the cryobot has melted to the ice-water interface. The hydrobot then swims off and "looks for life" with a camera and other instruments. This project was scheduled to start in 2001 and results are eagerly awaited.
In the meantime, researchers are finding that Antarctica is not a sterile, lifeless environment. Micro-organisms have been found to exist in the upper layers of the ice sheet and micro-organism fossils have been found in deep ice cores.
Colonies of bacteria are able to survive the long winters of extreme cold by a form of hibernation. In the Antarctic "summer", the warmth of sunlight is sufficient to melt small quantities of liquid water around dust particles acting as tiny solar collectors. It is at these sites that the bacteria wake up and go through their abbreviated life-cycles. Algae have also been discovered co-existing in these colonies - whose seeds over-winter and then "sprout" in the south polar summer. Ice cores drilled into the ice of Antarctica exhibit the presence of microbial life at all levels. Recent electron scanning microscope studies of these microfossils have revealed numerous forms that are not immediately identifiable. Research is underway to determine if these represent new varieties of microbial life.
Russian scientists have been able to revive and culture bacteria, yeast, fungi, and other microbes found in ice cores that carbon date to more than 200,000 years old! This is reminiscent of the bacteria that were found surviving in hibernation on the U.S. Surveyor moon lander that was retrieved by the Apollo astronauts, having outlasted the airless and hostile lunar environment for almost three years! Clearly, microbial life "goes on and on and on..." The implications of this ability of microbial life to be "long-suffering" are certainly provocative in terms of biologic viability in the extreme environments beyond Earth.
When the explorer Robert Falcon Scott discovered the Taylor Valley in Antarctica in 1903, he called it "a valley of the dead". But he was wrong. Antarctica is teeming with life in the form of microscopic plants and animals surviving under the permanently frozen surface and even in the rocks. These might help us to discover how life arose in the solar system, although so far it's only been detected on Earth.
One American scientist has said, "Given a little water and some bacteria to eat, these guts could really go for Mars."
Jupiter's Satellite Europa
Europa is a strange looking moon of Jupiter with a large number of intersecting features. It is unlike Callisto and Ganymede with their heavily cratered crusts. Europa has almost a complete absence of craters as well as almost no vertical relief. As one scientist put it, the features "might have been painted on with a felt marker". There is a possibility that Europa may be internally active due to tidal heating at a level one-tenth or less that of Io. Models of Europa's interior show that beneath a thin 5 km (3 miles) crust of water ice, Europa may have oceans as deep as 50 km (30 miles) or more. The visible markings on Europa could be a result of global expansion where the crust could have fractured, filled with water and froze.
The illustration "Ice Rafts" shows fragmented chunks of ice on Europa, similar in appearance to those seen in Earth polar seas during a springtime thaw. It's possible that Europa and Lake Vostok share a number of remarkable properties, including a kilometres-thick covering of ice over liquid water and an environment where life may have developed along unique evolutionary paths.
- Discovered by Galileo Galilei
- Date of Discovery 1610
- Distance from Jupiter 671,000 km
- Radius 1,565 km
- Mass 4.79982 × 1025 g
- Orbital Eccentricity 0.009
- Orbital Inclination 0.47 degree
- Orbital Period 3.55 days
- Rotational Period Synchronous
- Major Atmospheric Constituent Oxygen
Galilean Satellites of Jupiter: Io, Europa, Ganymede, Callisto. First observed by Galileo in 1610.
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