After drilling for two decades through more than two miles of antarctic ice, Russian scientists are on the verge of entering a vast, dark lake that hasn’t been touched by light for more than 20 million years. Scientists are enormously excited about what life-forms might be found there but are equally worried about contaminating the lake with drilling fluids and bacteria. (Courtesy of NOAA)

Russian scientists have drilled into the vast, dark and never-

before-touched Lake Vostok 2.2 miles below the surface of Antarctica, the state-run Russian news agency RIA Novosti reported Monday.

“Yesterday, our scientists stopped drilling at the depth of 3,768 meters and reached the surface of the subglacial lake,” the news agency quoted a source as saying. The team had “finally managed to pierce” the ice sheet into Vostok, the source said.

The report could not be verified Monday, but numerous Antarctica experts in the United States said they were hearing the same unconfirmed news. An official at the Russian Arctic and Antarctic Scientific Research Institute in St. Petersburg said Tuesday that a formal announcement would be coming out of Prime Minister Vladi­mir Putin’s office and that it was expected to be made soon.

It has taken the Russians more than 20 years to drill into the lake, operating in some of the most brutal weather conditions in the world. Their reported accomplishment comes just as the Antarctic summer ends at Vostok and the cold becomes so great that machinery can’t be operated and airplanes can’t come in or go out.

Because reaching the lake has been a high Russian priority in terms of the science and the engineering prowess it would suggest, a formal announcement is anticipated.

The Russian effort has created scientific excitement about potentially learning some of the long-held secrets of the largest subglacial lake in Antarctica, a body of water that wasn’t discovered until the mid-1990s and is the world’s third-largest lake by volume.

The long effort has met with controversy over some of the chemicals and techniques used in the drilling. Many have been concerned that pristine Lake Vostok — which hasn’t felt the wind for more than 20 million years and may well be home to previously unknown life forms — could be contaminated by the kerosene, Freon and other materials used in the drilling.

John Priscu of Montana State University, an Antarctica specialist who has been in periodic contact with the Russian team, said rumors are flying that the lake was indeed pierced but that no information has been formally announced.

“If they were successful, their efforts will transform the way we do science in Antarctica and provide us with an entirely new view of what exists under the vast Antarctic ice sheet,” he said in an e-mail.

Many scientists see Vostok as not only a last frontier on Earth but also a potential gold mine for learning about possible conditions on Jupiter’s moon Europa or Saturn’s moon Encedadus. Each is covered by a thick shell of ice with liquid water below, warmed by either the inner heat of the moon or by tidal forces.

The United States and Britain will begin drilling later this year into small subglacial Antarctic lakes. Scientists estimate that there are about 200 of these lakes beneath the ice sheet.

The research has importance for not only astrobiology — the search for life beyond Earth — but also for the dynamics of climate change. Antarctica holds about 70 percent of the planet’s fresh water as ice and subglacial liquid, and understanding whether and how it is changing is key to understanding possible future rises in global sea levels.

The Russians’ plan for this year’s Lake Vostok expedition has been to use a thermal drill on the last 30 feet of ice, pierce the lake and draw some of the water a short way up the borehole. The water will then freeze and be extracted late this year.

Russian scientists have been at Lake Vostok for more than 50 years, although they didn’t know they were drilling to a lake for the first 35. The then-Soviet team went to Vostok after the United States set up research facilities at the South Pole, about 900 miles away. The Russians chose the Vostok area because it is close to the “geomagnetic” South Pole, an important site for observing the Earth’s magnetic fields.

While many scientists are eagerly waiting for news about the piercing, many do not see substantial scientific data coming for a long time. Contamination remains an issue, as does the nature of the lake below.

Mahlon “Chuck” Kennicutt, a professor of chemical oceanography at Texas A&M University with expertise in polar dynamics, is one 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 wrote in an e-mail. “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 4 km with a straw that just brushes the top of the lake and then try to describe the lake from this incomplete picture.”

Correspondent Will Englund in Moscow contributed to this report.