This story originally aired on Feb. 12, 2003.
Lynne Cox is an American woman who's among the best ocean swimmers of our time. But there's something else about her that you may find hard to believe.
Science doesn't fully understand it, but she survives – she even thrives - in water that is cold enough to kill. It is so remarkable that researchers have been trying to figure out how she does it for 30 years.
As correspondent Scott Pelley first reported in 2003, when you combine her unique talents with a stubborn streak, there is only one thing left to do - try to swim a mile in the coldest water on earth.
In a world inhabited by penguins and seals, Cox decided to see whether she could survive swimming to Antarctica.
A continent larger than the United States, Antarctica lies frozen across the bottom of the world, hidden under cathedrals of ice in a world inhabited by penguins and seals. It's beautiful but dangerous. And no place on Earth is colder, more than 120 degrees below zero in winter.
Cox, 45, has traveled nearly 8,000 miles to test the limits of her endurance there. Wearing only a swimsuit, cap and goggles, this world champion plans to swim a mile in the kind of cold water that, even after all these years, still takes her breath away. It's a feat that no one on record has ever done and lived to tell the tale.
"It sort of just penetrates though your skin right away," she tells Pelley about first jumping in, "and you're immersed in it."
After an initial period of doubt about what she is doing, she says, she takes off like a shot. "I'm trying to get warm. It's freezing, it's really cold, you know?"
Pelley met Cox in southern California when she was training near her home. She started swimming in cold water as a child and taught herself to push the pain out of her mind.
"If you focus on the cold, then you're focusing on something that's not helping you get to where you need to get," she says.
At 14, she swam California's Catalina Channel — 21 miles in 12 hours. At 15, she set the women's and men's record in the English Channel. Then in 1987, in the midst of the Cold War, she was first to swim from Alaska to the Soviet Union — a five-mile swim through 40-degree water that warmed the Cold War.