You'd think that all the lakes on earth - at least the big and interesting ones - would have been explored by now. But there's a group of about seventy freshwater lakes that, believe it or not, have been sealed off from the atmosphere and from our eyes for hundreds of thousands of years. That's because these lakes lie beneath more than two miles of ice in Antarctica.

Detailed radar studies have shown that the largest lake is about the size of Lake Ontario. It's called Lake Vostok, after the Russian research station that lies above it.

Last year, scientists drilled through the ice to within about 400 feet of Lake Vostok, stopping short to avoid contaminating the water. Astronomers are very interested in whether there's any life in or near the lake, since the extreme conditions two miles below the ice may resemble those of some hostile reaches of our solar system, such as the moons of Jupiter.