Within the field of astrobiology, Earth-based analogues of habitable environments found in space (e.g., early Mars) can provide deep insights into our understanding of the possible evolution of extraterrestrial life. Within the context of ocean worlds such as Europa or Enceladus, our interest lies in what resides beneath the expansive ice cover of Antarctica: the subglacial lakes. These bodies of water are completely secluded from sunlight and have minimal interaction with the surrounding environment, rendering each lake unique. More than 400 lakes have been discovered under Antarctica so far.
In 2012, the British Antarctic Survey attempted to explore Lake Ellsworth, a subglacial lake lying 3.4 kilometres beneath the West Antarctic ice sheet, only to abandon halfway due to unsurmountable difficulties. A year later, the first successful retrieval of a clean sample from an Antarctic subglacial lake took place at Lake Whillans located 800 meters under the surface of a glacier on the other side of West Antarctica, 700 kilometres from the nearest open water. The borehole, no bigger than 60 centimetres in diameter, allowed samples of freshwater as well as sediments at the base of the lake (around 2 meters in depth) to be retrieved, after being trapped under the ice for more than 120,000 years. The samples contained almost 4,000 species of single-celled organisms thriving on the sediment on the lakebed despite the water being -0.49 °C (below 0 °C due to high pressures).
No review of subglacial lakes in Antarctica would be complete without mentioning the jewel of Antarctic exploration: Lake Vostok. Everything about Lake Vostok fascinates. First suggested in the early 1960s, Lake Vostok holds a volume of water bigger than Lake Michigan and is the largest of Antarctica’s subglacial lakes with an area of 12,500 square kilometres. It is situated at roughly 4,000 meters under the surface of the ice and 500 meters below sea level, with a maximum depth of up to ~900 meters making it amongst the deepest lakes in the world.
Its confirmation in 1993 has generated a great deal of excitement among scientists as it is thought to have been isolated from the outside world for over 15 million years when it was first covered with ice. This isolation has made Lake Vostok one of the most pristine and mysterious lakes on Earth and might contain valuable information about the history of life. The Russians, who have a research base on top of the lake, have drilled into the lake using crude technologies. In 2012, when they finally reached the lake after drilling through 3,769 meters of ice, water gushed up the borehole to 363 meters and froze. Alas, this water got mixed with the antifreeze compounds (freon and kerosene) used for the drill. Not only was there a risk of contamination within the lake itself, but the ice core of frozen lake water retrieved for analysis was compromised. Another hole was drilled three years later with lake water rising through the new borehole up to 70 meters. Within four days, this icy ‘cork’ was drilled into and frozen lake water was collected into a sterile receptacle.
In both cases, the water samples contained numerous microdroplets of drilling fluid, giving the ice a ‘milky’ appearance. Nevertheless, the samples were analyzed, unveiling a thriving microbial community. DNA sequencing of ice cores has identified hundreds of bacterial species, as well as archaea and fungi. The most intriguing discoveries include genetic material potentially associated with multicellular organisms. These include microscopic crustaceans, water fleas, a mollusc, and even a sea anemone.
While the possibility of contamination from drilling activities or past interactions with the ocean cannot be completely discounted, Vostok lifeforms could hint at some of the evolutionary pressures that might also exist under Europa and Enceladus.
It also suggests that life has remarkable adaptability to a wide range of conditions, raising the possibility of it being present in similar environments elsewhere in our solar system.
Future drills using cleaner technologies are being considered, and while we are still very far from exploring Lake Vostok using robotic submarines, there is no doubt that the technological advancements being developed for investigating Antarctic subglacial lakes will inform future missions to the subsurface oceans of our Solar System as well as provide astrobiologists with a better understanding of what may lie within them.
As I always say, we live in remarkable times! Happy Easter everyone.
Bernard