Europa on Earth - that's just what Antarctica's deep and dark Lake Vostok could be. A body of water the size of Lake Ontario, it lies beneath more than two miles of ice yet its waters are warm enough to potentially support life. Undiscovered until the 1990s, it since then became the goal of one of the great scientific quests of our time.

Finally, after more than 15 years of stop-and-go drilling, a team of Russian scientists and engineers did what hasn't been done in nearly 20 million years: They breached the pristine confines of Vostok.

The surface temperatures were a brutal -50 F when the drill reached 12,366 feet down and began to pull a small amount of ancient water a small way up the long borehole. Pressure changes and the retreat of some of the drilling fluids in the borehole confirmed the breakthrough and the team was ecstatic.

But with weather conditions worsening and the time soon coming when airplanes could neither fly into nor out of Vostok Station, the Russians had little chance to either celebrate or research further. Instead, they had to pack their bags and head north, leaving the quickly frozen Vostok water deep in the borehole to be retrieved late this year.

When the achievement was formally announced on Feb. 8, however, none of this really mattered: A deep sub-glacial lake in Antarctica had been pierced for the first time, and it happened at the largest, the deepest and the most intriguing of them all.

Scientists have located more than 200 subglacial lakes beneath the ice of Antarctica, and many of them no doubt hold remarkable secrets as well. But Vostok, by all accounts, is the "jewel of the crown."

Valery Lukin, the director of the Russian Arctic and Antarctic Research Institute, which conducted the expedition, was not at Vostok for the breakthrough, but he did make the formal announcement in Moscow and he called it an historic moment.

"Conditions in subglacial lakes in Antarctica are the closest we can get to those where scientists expect to find extraterrestrial life," he told the Interfax New Agency. "For me, the discovery of this lake is comparable with the first flight into space. It was equal, he said, "by technological complexity, by importance, by uniqueness."

Others certainly might object to putting the Vostok breakthrough at such an historic level, but there was great scientific excitement after the announcement.

Robin Bell, a glacialogist at the Columbia University's Lamont-Dougherty Earth Observatory, likened the achievement to "exploring another planet, except it's our own." And NASA chief scientist Waleed Abdalati said, "In the simplest sense, it can transform the way we think about life."

Or perhaps more precisely, it highlights for the public a transformation in understanding already embraced by the scientific community. Many researchers assume that microbial extremophiles live in Vostok, especially in the sediment of the bottom of the water and other areas where it touches land or ice.

They would be unlikely creatures, having not been exposed to sunlight - or anything formed through sunlight - for millions of years. But the assumption of their existence is based on years of exploration and research which has found extreme life throughout the glaciers of Antarctica, as well as on the deepest ocean floor, the driest deserts and miles down into the gold mines of South Africa.

This extremophile research includes work by John Priscu - a longtime polar researcher and professor of ecology at Montana State University, who, in 1999, published the first paper describing what kind of life we may find in Lake Vostok. Then in 2005, with his then postdoctoral student Brent Christner, he detected microbes in the ice core being drilled at Vostok by the Russians.

The Russian team has questioned the finding, saying that the microbes may be contamination from the drilling process. Priscu disagrees, and looks to the Vostok water for confirmation.

"I hope that they can confirm unequivocally that there is indeed microbial life in the lake," he said. "This has been the center of much debate in the past that can only be resolved with actual sample return. If they can confirm there is life in the lake, it will transform our view of Antarctica."

Priscu is part of the American team that will being drilling later this year into Subglacial Lake Whillians and the Whillans Ice Stream in West Antarctica, a project that will begin at about the same time as British drilling through the ice to Subglacial Lake Ellsworth, also in West Antarctica. Speaking again of the Vostok breakthrough, Priscu said that he suspects their data, along with results from Whillans and Ellsworth, not only will "transform the way we view the Antarctic continent" but also "will expand the limits of life on Earth."

Using his long experience as an Antarctic researcher, Priscu has been looking into how scientists can use the knowledge gleaned from polar research to think more clearly about, and ultimately explore, icy moons such as Europa and Enceladus. Both are known to have oceans of water beneath their thick ice crusts - quite like Vostok.

But if microbes or a signatures of their presence are found in the lake water, then does that mean Vostok is habitable and a potential model for those moons of Jupiter and Saturn? Chris McKay of NASA's Ames Research Center, a pioneer in extremophile work, said that while he expects Vostok does have "life" in it, the lake is not necessarily habitable.

By that he means microbes known to exist in the ice surrounding Vostok almost surely do make it into the lake. But McKay is unsure they would have the "food" needed to long-term survival.

"It may be that the environment in the lake does not provide an energy source of nutrients for life," he said. "Thus there may be life there carried in with the melting ice but there would not be an ecology. My guess is that this will be the case. Lake Vostok is uninhabitable but not sterile."

Mahlon "Chuck" Kennicutt, a professor of chemical oceanography at Texas A and M University with expertise in polar dynamics, is another of those cautioning against high near-term expectations.

"Physical and chemical measurements might establish whether the lake is fresh or salt water, whether it is normally- or over-pressured, and what other geochemistry may be apparent," he said. "The problem is that Lake Vostok is the size of Lake Ontario. You can imagine sampling Lake Ontario from a plane at a height of (2.3 miles) with a straw that just brushes the top of the lake and then trying to describe the lake from this incomplete picture."

Back at Vostok, the ice core will remain where it is for most of 2012, until it becomes warm enough for the Russian team to return and begin the complex work of pulling the Vostok sample out of the deep.

Researchers expect it to be particularly difficult to remove the ice core without contaminating it - and perhaps the lake - with the kerosene, antifreeze and Freon used to drill and to keep the borehole open during the long winter.

Indeed, scientists have been concerned for years about the Russian drilling techniques - about contamination and about the possibility of an explosive "de-gassing" of the high levels of oxygen and nitrogen in the water, rather like the way a soda bottle under pressure can explode when opened. Those often-expressed worries played a significant role in slowing down the drilling and making it a nearly two-decade project.

Priscu convened an international team of scientists for more than 10 years to address drilling issues, and he said the Russian team made some significant adjustments to their final approach as a result. He was in email contact with the team during the last weeks of the drilling, and he said by all accounts it went extremely well.

In addition to the potentially transformative astrobiology expected to come from Vostok and the other subglacial lakes, geologists and climate experts also will be studying the deep ice core for information about change over the eons. What is now Antarctica was once part of Australia, and it then supported tropical or near-tropical life. Recovering clues to when and how such changes took place could have relevance to the climate change debate today, the Russians in particular say.

The most compelling subglacial discoveries, however, may well be made if and when drills reach the sediment at the bottom of Vostok, or the other lakes. That's where the lake will be warmest and richest in nutrients, since it's closer to the heat of the Earth's core, or what some Russian researchers theorize is a large hydrothermal vent that warms the waters.

In either case, the lake bottom -which at its deepest point is about 3000 ft below its icy "surface" - is believed to be where microbes would most likely survive. The Russians have no known plans to drill deep into Vostok in the near future, but both the American and British teams do intend to penetrate the lakes and push down to their bottom surfaces.

Given the importance and size of the doubled-basined Vostok, which is 160 miles long and 30 miles wide, they also hope to participate in future drilling and research there. "If all our drilling efforts go well," Priscu said, "I think there's a good chance that we'll have an international expedition at Vostok in the years ahead."