The discovery of living microbes just above a hidden freshwater lake 2 miles deep in the frozen Antarctic extends the range of extreme conditions under which life is known to survive.

The finding, which researchers say almost certainly indicates there is a thriving community of microscopic creatures in the ancient, pristine lake, buoys hopes that life may exist elsewhere in the solar system. It also provides some clues about how and where to start looking.

Below an Antarctic glacier, in a spot nearly 10 times as deep as the Empire State Building is tall, lies what researchers believe to be a natural reservoir of fresh water known as Lake Vostok. It is deeper than Lake Tahoe and has an ice-locked "surface" that spans an area as big as New Jersey.

Researchers say Vostok, named for the Russian research station that sits above it, is the largest of nearly 80 sub-Antarctic lakes that have been mapped by airborne radio sounding. It has been known for two decades, and the recent discovery is a milestone during a years-long suspicion that there might be life trapped in the lake.

Intense pressure from the overlying ice generates heat which, combined with geothermal heat from below, is thought to keep the Vostok's million-year-old water in a liquid state. The ice also serves as an insulating blanket.

Some 393 feet (120 meters) above the lake rests the lower end of the deepest ice core ever drilled -- 11,886 feet (3,623 meters) below the frigid surface. There, in freshwater ice that researchers think has migrated upward from the lake, a community of microbes -- extremophiles, defined by the term -- thrive in some of the harshest conditions imaginable.

"There's a first principle among microbial ecologists that states 'Where there's water there's life,'" said Warwick Vincent, a professor of biology at Laval University, Canada. "Lake Vostok is the ultimate test of this principle in one of this world's most hostile places. These new discoveries imply that the 'life everywhere' adage will once again prove correct."

The newly discovered microbes have gone about their business of living sans any contact with the outside world for millions of years. But after running DNA analysis, a team led by John Priscu of Montana State University said the little critters are similar to modern-day organisms, including one called a proteo-bacteria.

"Our research shows us that the microbial world has few limits on our planet," Priscu said.

Vincent, who was not involved in the research, agreed with the other researchers in saying it appears the lake itself has "all the ingredients for an active microbial ecosystem."

It may be a while before that theory is proved, however. Drilling was stopped four years ago to prevent the introduction of anything that might contaminate the water. Delegates from several nations met in September to decide whether and how to explore the lake, but no firm proposal has been accepted.

Regardless, the discovery shows that an extremely cold, dark environment that is cut off from a ready supply of nutrients can still support life. Sealed off from the sources of energy most other known organisms use to survive, it seems the Vostok microbes live off things deposited long ago.

The fact that organisms have adapted to living in such harsh conditions bolsters the expectation that extraterrestrial life may be waiting to be discovered right here in our solar system. Jupiter's ice-covered moons Europa and Callisto, both thought to contain large oceans, have emerged in recent years as two of the most likely candidates.

Evidence shows that the massive gravity of Jupiter creates "tidal pumping," a pull on the moons, that might generate heat within. Europa, about the size of Earth's moon, has a surface temperature of minus 260 degrees Fahrenheit (minus 162 degrees Celsius), but the constant tugging of Jupiter's gravity may well create enough warmth to keep large parts of Europa's ocean liquid.

"Conditions on Europa are likely similar to those of the ice-covered lakes, but may not be analogous," Karl said. "If Europa has an internal energy pump, either through hydrothermal systems or via tidal pumping, then life may be better off than in Lake Vostok where microbes may be surviving off carbon and energy deposited there a million years ago."

Vincent, the Canadian biologist who also chairs the Canadian Committee for Antarctic Research, expressed both optimism and caution regarding the search for extraterrestrial life.

"The chemistry of the waters of Europa and Callisto appears to be very different relative to that in Lake Vostok," Vincent told space.com. "For example, these vast oceans (the largest in the solar system) are salty while all the evidence, including these most recent lake-ice analyses, shows that Lake Vostok is freshwater."

Scientists say convincing evidence of life on Europa may not come until robotic explorers venture below the surface.

A mission, the Europa Ice Clipper, is on the drawing boards. It would be a flyby-and-free-return mission designed to obtain samples of the europan sub-surface by dropping hollow copper spheres onto the icy surface. A "hydrobot" would map the undersea terrain and look for life. The samples would then be returned to Earth. No date is set for launch. The recent hunt for life in the Antarctic is expected to help build such future probes.

"I think that the Vostok experience may help in the design of biochemical and molecular probes for the search for life elsewhere," Vincent said. "It will also help in the design of sampling technologies, not only in terms of the challenge of sampling deep ice under conditions of extreme cold, but also in the development of environmentally friendly technologies that will reduce any lasting negative impacts of human exploration throughout the solar system."

Whatever we might find on Europa, Callisto, or any other body in the solar system won't likely look like any conventional alien, experts agree. Don't even expect a small fish, they say. But the mere discovery of simple microbial life elsewhere would hint at the likelihood that life is a far more common occurrence in the universe than we humans might have once thought.