The McMurdo Dry Valleys form the largest ice-free region in Antarctica. They also make up the coldest and driest environments on the planet. Yet, despite these extreme conditions, the valleys' surface is home to a large diversity of microbial life. Now, new evidence suggests that a vast network of salty liquid water exists 1,000 feet below the surface — a finding that lends support to the idea that microbial life may exist beneath Antarctica's surface as well. The finding isn't just exciting for Earth ecologists, however; planetary scientists are intrigued as well. Indeed, finding salty liquid water below Antarctica provides strong support for the idea that Mars, an environment that resembles Antarctic summers, may have similar aquifers beneath its surface — aquifers that could support microscopic life.
"We didn't know to what extent life could exist beneath the glaciers."
"[Before this study], we didn't know to what extent life could exist beneath the glaciers, beneath hundreds of meters of ice, beneath ice covered lakes and deep into the soil," says Ross Virginia, an ecosystem environmentalist at Dartmouth College and a co-author of the study, published in Nature Communications today. This study opens up "possibilities for better understanding the combinations of factors that might be found on other planets and bodies outside of the Earth" — including Mars.
Approximately 4.5 billion years ago, 20 percent of the Martian surface was likely covered in water. Today, Mars may still be home to small amounts of salty liquid water, which would exist on the planet's soil at night before evaporating during the daytime. Taken together, these findings are pretty exciting for those who hope to discover life on Mars — water, after all, is a requirement for life. Unfortunately, researchers have also pointed out that the Martian surface is far too cold for the survival of any known forms of life. That's why some scientists have started to wonder about what may lie beneath the Martian surface. If the extreme environment conditions found in Antarctica's subsurface contains all the elements necessary for life, it's possible that the Martian subsurface might as well.
In the study, researchers flew a helicopter more than 114 square miles over Taylor Valley — the southernmost of the three dry valleys. Below the helicopter, researchers suspended a large antenna. The technology, called SkyTem, acted as an airborne electromagnetic sensor that generated an electromagnetic field capable of penetrating through ice or into the soil in the dry valley. As the antenna surveyed the valley, the electromagnetic field reflected back information that was altered from the original signal depending on whether it encountered a brine or frozen soil or ice, Virginia explains. "So basically we're inferring the distribution of those types of materials based on what is reflected back to these helicopters flying over the surface of Antarctica."
"probably much more extensive subsurface environments in Antarctica where life might exist."
The results of this study indicate that unfrozen brines — salty and slightly thick water solutions — form an extensive system of interconnected aquifers beneath frozen soils, lakes, and glaciers. The brines may be the result of ancient ocean deposits. They may also be the remnants of an evaporated or frozen ancient lake. "By flying this technology for the first time in Antarctica, we were able to determine that there is this extensive subsurface environment that isn't frozen that contains water and salt at temperatures at which microbial life is expected to exist," Virginia says. And that means that "there are probably much more extensive subsurface environments in Antarctica where life might exist."
an extensive system of interconnected aquifers beneath frozen soils
The idea that life may exist in unfrozen brines below Antarctica didn't pop out of nowhere. Jill Mikucki, a microbiologist at University of Tennessee and a co-author of this study, has spent some time analyzing brines samples in Blood Falls — an area in the Antarctic that exudes red-colored subglacial brines that are pushed to the surface. "Without drilling, this is our own natural portal for looking at what these brines might be about," Virginia says. Thanks to this work, Mikucki found that the brines are about twice as salty as ocean water. "They also contain densities of microbial cells that are similar to groundwater found in other areas," he says.
Moreover, the researchers confirmed their findings regarding the composition of the subsurface by comparing their results to those obtained by researchers who were allowed to drill boreholes into the soil in a small area of the Antarctic in the 1970s. "We took the instrument and flew it over the same zones, and found very similar patterns and results," Virginia says.
Now that this initial study is complete, Virginia and his team are hoping to return to survey a larger area using more recent technology. This kind of research is important because it provides an opportunity to ask a set of new questions about what the limits to life are, where life exists on Earth, and how widespread these ecosystems might be, Virginia says. "I think that habitats suitable for life are just about everywhere on this planet, and learning about these environments is important not only for understanding life on Earth but also for understanding life on other planets," he says. "Fundamentally this type of work just tells us more about ourselves." Besides, "we need to understand Earth, to understand Mars."