Credit:  Mark Thiessen

By Michael D. Lemonick, July, 2014, Nationalgeographic.com

An electronic signal travels from NASA's Jet Propulsion Lab in Pasadena, California, to a robotic rover clinging to the underside of foot-thick ice on an Alaskan lake. The rover's spotlight begins to glow. "It worked!" exclaims John Leichty, a young JPL engineer huddled in a tent on the lake ice nearby. It may not sound like a technological tour de force, but this could be the first small step toward the exploration of a distant moon.

More than 4,000 miles to the south, geomicro­biologist Penelope Boston sloshes through murky, calf-deep water in a pitch-dark cavern in Mexico, more than 50 feet underground. Like the other scientists with her, Boston wears an industrial-strength respirator and carries a canister of spare air to cope with the poisonous hydrogen sulfide and carbon monoxide gases that frequently permeate the cave. The rushing water around her feet is laced with sulfuric acid. Suddenly her headlamp illuminates an elongated droplet of thick, semitransparent fluid oozing from the chalky, crumbling wall. "Isn't it cute?" she exclaims.

These two sites—a frozen Arctic lake and a to­xic tropical cave—could provide clues to one of the oldest, most compelling mysteries on Earth: Is there life beyond our planet? Life on other worlds, whether in our own solar system or orbiting distant stars, might well have to survive in ice-covered oceans, like those on Jupiter's moon Europa, or in sealed, gas-filled caves, which could be plentiful on Mars. If you can figure out how to isolate and identify life-forms that thrive in similarly extreme surroundings on Earth, you're a step ahead in searching for life elsewhere.